Research ArticleBehavior of Concrete-Filled Steel Tube Columns Subjected toAxial Compression

Pengfei Li Tao Zhang and Chengzhi Wang

Chongqing Jiaotong University Chongqing 400074 China

Correspondence should be addressed to Pengfei Li lipengfeicqjtueducn

Received 21 March 2018 Revised 27 July 2018 Accepted 5 August 2018 Published 26 August 2018

Academic Editor Jose A Correia

Copyright copy 2018 Pengfei Li et al +is is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

+e behavior of concrete-filled steel tube (CFST) columns subjected to axial compression was experimentally investigated in thispaper Two kinds of columns including CFST columns with foundation and columns without foundation were tested Columnsof pure concrete and concrete with reinforcing bars as well as two steel tube thicknesses were considered+e experimental resultsshowed that the CFST column with reinforcing bars has a higher bearing capacity more effective plastic behavior and greatertoughness and the elastoplastic boundary point occurs when the load is approximately 04ndash05 times of the ultimate bearingcapacity +e change of rock-socketed depth and the presence of steel tube will affect the ultimate bearing capacity of rock-socketed pile +e bearing capacities of the rock-socketed CFST columns are lower than those of rock-socketed columns withouta steel tube under a vertical load besides the greater the rock-socketed depth the greater the bearing capacity of the rock-socketedpiles In addition a numerical comparison between the ultimate load and the theoretical value calculated from the relevantspecifications shows that the ultimate load is generally considerably greater than the theoretical calculation results

1 Introduction

In the last few decades high-rise large-span and large-scalebuilding structures have become more common Concrete-filled steel tubular (CFST) members are well recognized fortheir excellent performance owing to the combined merits ofsteel and concrete materials [1] +erefore concrete-filledsteel tubes are being increasingly used in high-rise buildingsand in large-span structures CFST columns have been usedin earthquake-resistant structures and bridge piers subject toimpact from traffic and used to support storage tanks decksof railways and high-rise buildings as well as being used aspiles Concrete-filled steel tubes require additional fire-resistant insulation if the fire protection of the structureis necessary [2]

Studies of CFST have also been frequently performedand tests of CFSTwith rectangular square and circular crosssections filled with high-strength concrete have been re-ported [3ndash6] including compression [7ndash12] bending[13ndash17] or torsion [18ndash20] tests +e influence of the be-havior and strength capacity of CFST on the bonding and

local buckling of the steel profile confinement of the con-crete and strength of the materials were discussed Pull-outtests on CFSTcolumns have shown the contribution of shearconnectors to the force transference mechanism that occursin beam-column connections Local buckling has beenwidely studied and it is possible to consider its influence onthe strength capacity of the CFSTcolumns +e confinementeffect is influenced by the shape of the cross section thethickness of the steel profile the type of loading the slen-derness of the composite column and the strength of thematerials used +e studies on CFST rock-socketed columnsand predicting the ultimate capacity of CFST columnssubjected to axial compression are limited and there is nostandard method for calculating the strength of concrete-filled steel tube with reinforcing bars

+ere are several design codes for concrete-filled steelcolumns such as the America Institute of Steel Construction(AISC) Load and Resistance Factor Design (LRFD) [21]Eurocode 4 (EC4) [22] Brazilian Code NBR 8800 [23 24]and GB50396-2014 [25] Since the AISC is focused on steelcolumns use of the AISC [21] specifications is limited to

HindawiAdvances in Materials Science and EngineeringVolume 2018 Article ID 4059675 15 pageshttpsdoiorg10115520184059675

composite columns with steel yield stress and concretecylinder strength no greater than 415 and 55MPa re-spectively Modified values for both the yielding strength(fmy) and elasticity modulus (Em) are assumed +esemodified terms take into account the presence of the con-crete filling the steel profile EC4 [22] and NBR 8800 [23 24]determine the resistance capacity of a section by adding thecontribution of the steel tube and the concrete core Forcolumns with circular cross sections the confinement effectis considered by using coefficients that increase the uniaxialcompressive strength of the concrete (fck) and reduce theyielding strength of the steel (fy) +e instability in thesestandard codes is considered by using a coefficient whichdepends on the slenderness of the composite column Limitsfor the steel tube slenderness are also considered to avoidlocal buckling

In China reinforced CFST piles are widely used infoundations of piers and bridges for its good mechanicalproperties for instance Orchard Container pier inChongqing Port Cuntan pier Xintian Container pier inWanzhou Port and Yangshuo pier in Wuhan Port +eremarkable feature of this new structure is that the thicknessof the steel pipe is thin and the ratio of diameter to thicknessis very large [26] It greatly exceeds the allowable range of themuch existing specifications [27] for example the ferrulecoefficient of circular-section concrete-filled steel tubularmembers specified in Chinese specification [28] should belimited to between 03 and 30 and the ratio of diameterto thickness (Dt) should be limited to the following range20

235fy

1113969leDtle 85

235fy

1113969 Eurocode 4 (EC4) [22]

explicit limits the allowedDt values in the European contextto 90lowast 235fy +e maximum allowable value of diameter-thickness ratio (Dt) specified in AISC [21] is 031lowast Efy Soit is an attempt to estimate the ultimate load of reinforcedCFSTpiles by above codes and it may provide a reference forthe design and research of the new structure with largediameter-to-thickness ratio

+e present paper is thus an attempt to study the be-havior of concrete-filled steel tube columns with foundationand columns without foundation subjected to axial com-pression +e main objectives of this paper were twofoldfirst to discuss the bearing capacity of CFST columns undervertical load with regard to the thickness of steel tube re-inforcement and the depth of rock-socketing second todiscuss the ultimate load experimental results and theo-retical calculations

2 Experimental Study

21 Columns without Foundation

211 Test Program +e experimental study of concrete-filled steel tube columns subjected to axial compression wasaccomplished with several objectives namely the evalua-tion of the accuracy of several design codes to predict theresistance capacity to determine the maximum load ca-pacity of the concentric loading specimens and to in-vestigate the failure pattern before and after the ultimateload is reached

+e specimens were tested a summary of their prop-erties is presented in Table 1 and the schematic of pile isshown in Figure 1 +e cross sections of the tested columnsare circular the length of each column specimen is 1200mmand the diameters of the specimens are either 150mm(symbolized with ldquo1rdquo) or 165mm (symbolized with ldquo2rdquo)thickness of the steel tube are either 12mm (symbolizedwith ldquoArdquo) or 16mm (symbolized with ldquoBrdquo)

212 Properties of theMaterials +e concrete was producedin the laboratory of the Structural Engineering Departmentand the mechanical properties of the concrete core weredetermined by cylinder tests (150mmtimes 150mmtimes 150mm)In addition the concrete mix ratio is shown in Table 2 +econcrete grade is C30 the mixing ratio of cement sandstone water for ordinary Portland cement with a cementstrength grade of M325 is 1 228 407 065 (mass ratio)the gravel underwent natural drying after washing and itranged from 5 to 10mm in diameter During the casting ofthe specimen three standard concrete cube specimens of150mmtimes 150mmtimes 150mm are reserved for each batch ofconcrete and the standard cube test block is sprinkled for 28days for concrete axial compressive strength test +ecompressive strength of concrete cube specimens is shownin Table 3 According to the yield strength test of steel barsthe stress-strain curve of steel bars is obtained +e yieldstrength of steel bars is 375MPa and the ultimate yieldtensile strength is 410MPa as is shown in Table 3

In Table 4 E is equal to the modulus of elasticity AHRB335 steel plate is used for the steel-retaining materialand it is welded to a steel sleeve with a thickness of either12mm or 16mm and the steel bar is a two-stage rib barwith a diameter of 6mm

213 Test Setup All of the tests were performed in a verticalcolumn-testing machine with a static load capacity of5000 kN as is shown in Figure 2 +e upper and lowersurfaces of the column are respectively connected with theloading device and the rigid base plate by using a rigid pad+e load is divided into 12 stages according to the estimatedultimate carrying capacity but the load grading is notconsistent during the initial stage the loading is larger butthe loading grading is gradually reduced after the plasticstage of deformation is reached +is loading scheme allowsthe study of the post-peak behavior of the composite col-umns +erefore it is possible to study the elastic behaviorthe axial load capacity and the ductility of the columnsunder axial loading

For this test three layers of strain gauges were arrangedvertically along the column and the data were collected bya signal acquisition system to explore the variation in thestrain of the steel casing with an applied load Besides thedistance between the first strain gauge and the column topand the distance between the bottom strain gauge and thepile bottom were both 30 cm and the distance betweenadjacent strain gauge layers was 30 cm+e 4 strain gauges ineach layer were arranged symmetrically along the columnsurface And an additional strain gauge was embedded in the

2 Advances in Materials Science and Engineering

concrete and the strain of the concrete wasmeasuredwith thechange in the load In these tests each strain gauge was di-vided into vertical and horizontal measuring points therefore12 strain gauges a total of 24 points were placed on theoutside of each specimen Additionally four displacementgauges are arranged symmetrically on the pile top and the pilebottom to measure the change in the compression of the pilewith the load during the loading process these results wereused as the basis of the loading control method

22 Columns with Foundation

221 Test Program +e test program for the columns withfoundation is approximately consistent with that of the

concrete-filled steel tube columns without foundation thecross sections of these columns are also circular and all thecolumns were filled with C30 concrete +e specimens weretested and a summary of their properties is presented inTable 5 +e length of each column specimen is 800mm thediameter of each is 100mm and the size of foundation is21mtimes 13mtimes 1m

222 Properties of the Materials +e concrete for thecolumns was produced with high-strength M30 cementmortar with a cement quartz sand water mix ratio of 1 176 032 (mass ratio) +e diameter of the steel tube is100mm its thickness is 1mm and its elastic modulus isapproximately E 200GPa Additionally the main bar ofsecondary reinforcement has a diameter of 6mm and thestirrups have a diameter of 1mm +e stirrups spacing is3 cm in the column

Due to the large size of the test foundations they cannotbe excavated to the laboratory so concrete was used tosimulate the rock foundation Mudstone is susceptible toweathering which leads to a reduction in the bearing ca-pacity of the pile therefore the concrete strength is low tosimulate strong weathering mudstones +e concrete mixratio is 125 cementitious material 125 stone and 50sand After 28 days of curing testing results showed that thecompressive strength of the standard concrete was 300KPaand the elastic modulus was 16MPa

+e pile was formed as shown in Figure 3 In additionthe material properties of the concrete core and steel tube areshown in Table 6

223 Test Setup +e loading system uses a split hydraulicjack with a limit load of 200 kN When the loading device isinstalled the load sensor can be placed on a piece of steelplate on top of the pile and the loading apparatus isa separate hydraulic jack that is placed on top +e top of the

Table 1 List of columns for CFST columns without foundation

Specimens D times δ times L

(mm)

Ac(mm2)

Ar(mm2)

As(mm2)αsc()

PL-2 165times 0times1200 21382 0 0 0NS-A-2 165times12times1200 21382 0 622 29NS-B-2 165times16times1200 21382 0 829 39RN-2 165times 0times1200 21382 170 0 08RS-A-2 165times12times1200 21382 170 622 37RS-B-2 165times16times1200 21382 170 829 47PL-1 150times 0times1200 17671 0 0 0NS-A-1 150times12times1200 17671 0 570 32RS-A-1 150times12times1200 17671 170 570 41RS-B-1 150times16times1200 17671 170 762 52Notation D outside diameter of the circular steel tube δ wall thickness ofthe steel tube L length of the specimens Ac concrete cross-sectional areaAr reinforced cross-sectional area As steel cross-sectional area αsc steelratio PL plain concrete RS concrete-filled steel tube column with rein-forcing bars NS concrete-filled steel tube column without reinforcing barsand RN concrete column with reinforcing bars A thickness of steel tube is12mm B thickness of steel tube is 16mm 1 diameter is 150mm 2diameter is 165mm

Φ250Outer stirrups

5Φ6

Φ(12) t(AB)Steel tube

Φ2100Inner stirrups R

300

300

300

300

L=

1200

Strain gauges

Figure 1 Schematic of the specimens and arrangement of thestrain gauges around the columns

Table 2 Concrete mix ratio

Grade Concrete mixratio

Cement(kgm3)

Water(kgm3)

Stone(kgm3)

Sand(kgm)

C30 065 300 195 1220 685

Table 3 Mechanical properties of the concrete and steel tube

Specimens fcu (MPa) fy (MPa)PL-2 321 mdashNS-A-2 346 375NS-B-2 349 375RN-2 312 375RS-A-2 337 375RS-B-2 335 375PL-1 348 mdashNS-A-1 329 375RS-A-1 334 375RS-B-1 341 375

Table 4 Material properties of the concrete and steel tube

Types Grade E (MPa) ΝConcrete C30 275E+ 04 02Reinforcement HRB335 210E+ 05 03Steel HRB335 210E+ 05 03Stirrups HRB335 210E+ 05 03

Advances in Materials Science and Engineering 3

(a) (b)

Figure 2 Test setup (a) General view (b) CFST detail

Table 5 List of columns for CFST columns with foundation

Specimens D (mm) h (mm) n (n hD) Steel tube (mm)Z1P1 100 300 3 1Z1P2 100 300 3 0Z2P1 100 400 4 1Z2P2 100 400 4 0Z3P1 100 500 5 1Z3P2 100 500 5 0Notation Z1 rock-socketed depth is 300mm Z2 rock-socketed depth is 400mm Z3 rock-socketed depth is 500mm P1 steel tube is 1mm P2 steel tube is0mm h rock-socketed depth n ratio of rock-socketed depth n hD

(a) (b)

Figure 3 Properties of the materials (a) General prefabricated piles (b) Steel tube prefabricated piles

4 Advances in Materials Science and Engineering

jack is xed to the reaction beam and the device diagram isshown in Figure 4 During step-by-step loading to keep eachload the same the load is calculated according to 10 of theestimated carrying capacitye rst stage load is 2 times thegrading load the unloading is reduced by a consistent 20 ofthe carrying capacity e requirements are that thetransmission load is uniform continuous and stable andthat the time of loading is at least 1 minute

3 Test Results and Discussion

31 Columns without Foundation

311 Failure Modes e typical failure modes of thespecimens in this test are as followse failure modes of theplain concrete specimen (PL-2) and the reinforced concretespecimen (RN-2) are shown in Figures 5(a) and 5(b) emain failure mode is the fracture of the top concrete and thecrushing range is about one quarter of the length of the pile

e typical failure mode of the unreinforced CFSTspecimens (NS-A-2 and NS-B-2) is shown in Figure 5(c)which is mainly represented by the local buckling of thespecimen after concrete crushing

e reinforced CFST piles exhibit two dierent failuremodes e specimens with the thickness of 16mm of steelcasing (RS-B-1 and RS-B-2) locally exhibit buckling de-formation during loading the local deformation is graduallyincreased with the loading and the specimen is bent anddeformed until the bearing capacity is nally lost as shownin Figure 6(a) e specimens with the thickness of 12mm(RS-A-1 and RS-A-2) showed the same deformation char-acteristics as the specimen RS-B-1 in the early stage ofloading but when the load reaches 850 kN the weld of thesteel casing suddenly opened e specimen is destroyedinstantaneously as shown in Figure 6(b) In summary twodierent types of damage may occur in reinforced CFSTwhen axially compressed

(1) When the weld strength of the steel casing is greaterthan the axial load limit of the composite memberthe failure mode is the bending failure caused by thelocal buckling deformation which is a ductile failurefeature

(2) When the weld strength of the steel casing is less thanthe axial load limit of the composite member thefailure mode is the open splitting of the steel casingweld under the expansion stress of the concretewhich is a brittle failure feature

312 Load-Displacement Curve

(1) Reinforced and Unreinforced CFST Members e load-vertical displacement curves of reinforced CFST specimenswith steel casing thickness of 12mm (RS-A-2) and 16mm(RS-B-2) are shown in Figure 7 It can be seen from the testresults that when the thickness of the steel casing increases to16mm the displacement of the top of the specimen with theload is the same as that of the thickness of 12mm and bothexhibit obvious plastic failure properties the proportionallimit of two thicknesses is relatively close which is ap-proximately 600 kN Before the load reaches 600 kN theload-displacement curves of the two test pieces are basicallycoincident When the load exceeds 600 kN that is afterentering the plastic zone the absolute value of the dis-placement increment under the same load increment issmaller than the case where the thickness of the steel casingis 12mm under the same condition It indicates that therestraining eect of the steel casing on the core concrete ismainly reected in the plastic zone of the component whilethe eect on the elastic zone is small e maximum dis-placement that can be achieved with a thickness of 16mm is138mm which is greatly improved compared to thethickness of the steel casing of 12mm erefore thethickness of the steel casing has a great inuence on theductility of the reinforcing member and the improvement ofits bearing capacity

e load-vertical displacement curves of CFST speci-mens with steel tube thickness is 12mm (RS-A-2 and NS-A-2) and t steel tube thickness is 16mm (RS-B-2 and NS-B-2)composite members are shown in Figures 8 and 9

Steel tubeP1P2

Foundation21m times 13m times 1m

Hydraulic jacks

Load cell Displacement meter

L=

800m

m

h

Figure 4 Test setup (hmeans rock-socketed depth P1 steel tube is1mm P2 steel tube is 0mm)

Table 6 Material properties of the concrete core and steel tube

Steel tube Concrete Reinforcedbar

Steel tube(mm)

D 100mm M30 D 6mm Ec 16MPat 1mm mdash mdash fy 300KPa

Es 200GPaC S W 1 176

032 mdash mdash

Advances in Materials Science and Engineering 5

It can be obtained from the test results that the pro-portional limit of the load-vertical displacement curve ofreinforced CFST piles is slightly higher than unreinforcedones and the proportional limit of the specimen RS-A-2 andRS-B-2 is about 600 kN greater than 500 kN of test NS-A-2and NS-B-2 At the same time the ultimate deformationcapacity of reinforced CFST composite members is betterthan that of unreinforced CFST specimens It can be seenthat in the elastic stress stage the presence of the stressedsteel bars delays the generation of concrete cracks therebyincreasing the proportional limit of the test In the plasticstage the stressed steel bars play a further restraining roleon the core concrete which inhibits the formation and

expansion of the crack and improves the ductility and ul-timate deformation ability of the test

(2) Encased and Nonencased Members +e load-verticaldisplacement curves of plain concrete specimen (PL-2)and reinforced concrete specimen (RN-2) and reinforcedCFST composite members (RS-A-2 and RS-B-2) are shownin Figure 10 It can be seen from the test results that the steeltube has a great influence on the bearing capacity and de-formation capacity of the test For the plain concretespecimen (PL-2) the ultimate bearing capacity and ultimatedeformation are small and the maximum displacement is287mm showing the characteristics of brittle failure For the

(a) (b)

(c)

Figure 5 Failure modes (a) Plain concrete pile (b) Reinforced concrete pile (c) Unreinforced CFST pile

6 Advances in Materials Science and Engineering

reinforced concrete specimen (RN-2) the load-displacementcurve shows a certain ductility characteristic but the ultimatebearing capacity and ultimate deformation of the specimenare signicantly smaller than the reinforced CFST compositemember

313 Strain Development In this paper the strain law of thesteel casing and concrete core under the condition of an axialcompression load is described for the specimens with a steeltube thickness of 12mm (specimen RS-A-2) and 16mm(specimen RS-B-2) During the test the vertical strain andhoop strain on the side of the steel casing were monitoredand the development rule of the compressive strain inside

the core concrete was monitored Among them four straingauges are arranged on the side of the steel casing at the topandmiddle and top of the test specimen in the circumferentialdirection and the vertical strain and lateral strain of the steelcasing at this position are measured respectively In the dataprocessing the strain values of four measuring points in thesame plane are averaged to obtain the average strain of thesteel casing at the plane e load-strain curve and averagestress-strain curve of the test piece are given below Amongthem the average stress is obtained by dividing the axial loadon the specimen by the cross-sectional area

e developments of the longitudinal strain circum-ferential strain and compression behavior of the steel tubeare shown in Figures 11ndash16 Figures 11ndash13 are laws of strain

(a) (b)

Figure 6 Failure modes of reinforced CFST pile (a) Buckling deformation (b) Splitting of the steel casing weld

1200

1000

800

600

400

200

00 2 4 6 8 10 12

RS-A-2RS-B-2

14Vertical displacement (mm)

Load

(kN

)

Figure 7 Vertical displacement-load curves of two thickness steeltube-reinforced CFST piles

1000

800

600

400

200

00 2 4 6 8 10 12

RS-A-2NS-A-2

14Vertical displacement (mm)

Load

(kN

)

Figure 8 Comparison of reinforced and unreinforced CFST pileswith thickness is 12mm

Advances in Materials Science and Engineering 7

development of specimen RS-A-2 and Figures 14ndash16 arelaws of strain development of specimen RS-B-2

From the above test results it can be seen that for thesteel casing-reinforced concrete composite member thestrain value in the middle of the specimen is slightly largerthan the top and bottom strain values e strain devel-opment of steel casings at each measuring point showselastic-plastic characteristics with the increase of load Be-fore the axial load value is less than 045 times the ultimateload of the model pile foundation the load and strain showa linear relationship while the load reaches 045 times theultimate load carrying capacity After the capacity under thesame load increment the strain increment gradually in-creases showing a nonlinear characteristic From the wholeload-strain curves of the reinforced CFST specimens itexhibited the characteristics of ductile failure

In summary the use of a steel tube plays a very im-portant role in improving the compressive deformation andmechanical properties of the components For a joint steeltube-reinforced concrete structure the bearing capacity andthe ductility of the components are greatly improvedcompared to the specimens with no steel which is due to theexistence of the internal structure of the composite structureeectively enhancing the constraints between the concreteparticles to limit the development of microcracks and theeective stress

32 Columnswith Foundation It can be seen from Figure 17that the variation in the results of the dierent model col-umns under the load at the pile top is consistent and it canbe considered that the inuence of a rockless cylinder on the

1200

1000

800

600

400

200

00 2 4 6 8 10 12

RS-B-2NS-B-2

14Vertical displacement (mm)

Load

(kN

)

Figure 9 Comparison of reinforced and unreinforced CFST piles with thickness is 16mm

1000

800

600

400

200

00 2 4 6 8 10 12

RS-A-2PL-2RN-2

14Vertical displacement (mm)

Load

(kN

)

(a)

1200

1000

800

600

400

200

00 2 4 6 8 10 12 14

Vertical displacement (mm)

Load

(kN

)

RS-B-2PL-2RN-2

(b)

Figure 10 Comparison of plain concrete reinforced concrete and reinforced CFST piles

8 Advances in Materials Science and Engineering

settlement of a rock-socketed column is also consistent Itcan be seen from Figure 17 that the displacements of Z1P1and Z1P2 are basically the same from the load values of zeroto 9 kN the load-vertical displacement curve is approxi-mately a straight line and the two piles are in the elasticstage After the load exceeds 9 kN the displacement rate ofthe Z1P1 pile exceeds that of the Z1P2 pile and the settle-ment of the pile top increases e load-vertical displace-ment curves of the two piles change slowly and the processof steep drop is not obvious Figure 17 shows several settlingsthat may be due to the inhomogeneity of the model

foundation According to the above analysis it can be seenthat the vertical bearing capacities of CFST rock-socketedpiles are weaker than those rock-socketed piles withouta steel tube the dierence is mainly because the rock-socketed pile without a steel tube has a concrete-rock in-terface with a coecurrencient of friction greater than that of theCFST rock-socketed pile with a steel-rock interface

As seen from Figure 18 the greater the rock-socketeddepth the greater the load-bearing capacity of the rock-socketed piles In addition when the depth of the pile in therock-socketed increased from 3D to 5D the vertical ultimate

1000

800

600

400

200

00 2000 4000 6000

Strain (με)8000 10000 12000

Top verticalBottom verticalCentral vertical

Load

(kN

)

(a)

50

40

30

20

Ave

rage

stre

ss (M

Pa)

10

0

Strain (με)2000

Top verticalBottom verticalCentral vertical

4000 6000 8000 10000 120000

(b)

Figure 11 Vertical strain development laws of specimen RS-A-2 with steel casing (a) Relationship of vertical strain development with load(b) Relationship of vertical strain development with average stress

1000

800

600

400

200

0 1000 2000 3000Strain (με)

4000 5000 6000 7000 8000

Load

(kN

)

Top loopBottom loopCentral loop

0

(a)

50

40

30

20

10

00 1000 2000 40003000

Strain (με)5000 6000 7000 8000

Ave

rage

stre

ss (M

Pa)

Top loopBottom loopCentral loop

(b)

Figure 12 Loop strain development of specimen RS-A-2 with steel casing (a) Relationship of loop strain development with load (b)Relationship of loop strain development with average stress

Advances in Materials Science and Engineering 9

bearing capacity increased by approximately 40 e mainreason for this eect is that with the increase in the rock-socketed depth the contact area will increase and althoughthe side friction coecurrencient does not change the total frictionof the pile will signicantly increase therefore the verticalbearing capacity of the pile is signicantly improved It isfound that the vertical ultimate bearing capacity of rock-socketed piles without a steel tube (steel-free cylinder) isapproximately 10 higher than that of the steel-retainingtube when the depth of rock-embedment is the same emain reason for this phenomenon is that the outer wall ofthe pile is very smooth since its roughness is much smallerthan the concrete the corresponding side friction is lower

and the ultimate bearing capacity of the pile is equal to thepile side friction and pile end resistance decreasing theultimate bearing capacity of the pile

4 Analysis of the Ultimate Load

According to EC4 [22] the axial load capacity (NplRd) ofa CFST column can be determined by summing the yieldload of both the steel section and concrete core Forconcrete-ned tubes of circular cross section account maybe taken of increase in strength of concrete caused byconnement provided that the relative slenderness λ doesnot exceed 0 5 and edlt 0 1 where e is the eccentricity of

0 200 400 800600 1000

Concrete

1200 1400 1600Strain (με)

500

600

700

400

300

200

100

0

Load

(kN

)

(a)

Concrete

0 200 400 800600 1000 1200 1400 1600Strain (με)

30

35

25

20

15

5

10

0

Ave

rage

stre

ss (M

Pa)

(b)

Figure 13 Axial compressive strain development of core concrete of specimen RS-A-2 (a) Relationship of vertical strain development withload (b) Relationship of vertical strain development with average stress

0 2000 4000 80006000Strain (με)

10000 12000 14000

Top vertical

Bottom verticalCentral vertical

1000

1200

800

600

400

200

0

Load

(kN

)

(a)

0 2000 4000 80006000Strain (με)

10000 12000 14000

Top verticalMiddle verticalBottom vertical

50

60

40

30

20

10

0

Ave

rage

stre

ss (M

Pa)

(b)

Figure 14 Vertical strain development laws of specimen RS-B-2 with steel casing (a) Relationship of loop strain development with load (b)Relationship of loop strain development with average stress

10 Advances in Materials Science and Engineering

loading given by MEdNEd and d is the external diameter ofthe column e plastic resistance to compression may thenbe calculated from the following expression in equations(2)ndash(5) e application of EC4 [22] is restricted to com-posite columns with steel yield stress and concrete cylinderstrength of less than 355 and 50MPa respectively efollowing presents the formulations of the AISC [21] EC4[22] NBR 8800 [23 24] and GB50396-2014 [25] standardcodes to determine the resistance capacity of axially loadedCFST columns And rs is the radius of gyration of the steelhollow section le is the length of the column Ec is themodulus of elasticity of the concrete and Es is the modulusof elasticity of the steel e formulations presented were

used to calculate the compressive strength of the axiallyloaded CFST columns investigated in the present study Inaddition the boundary conditions of the testing approachare upper if the pile is loading and lower if the pile is xed

In GB50396-2014 [25] θ means the hoop coecurrencient ofconcrete-lled steel tubular members θ αscffc αsc rep-resents the steel content of concrete-lled steel tubularmembers in the design of compressive strength of concrete-lled steel tube piles B and C are the inuence factors of thecross-sectional shape on the hoop eect and about circularcross section B 0176lowast f213 + 0974 Cminus0104fc144+ 0031 In AISC [21] the axial compression member isconsidered to be the overall stability of the member the

0 1000 2000 40003000Strain (με)

5000 6000 7000

Top loopCentral loopBottom loop

1000

1200

800

600

400

200

0

Load

(kN

)

(a)

0 1000 2000 40003000Strain (με)

5000 6000 7000

Top loopCentral loopBottom loop

50

60

40

30

20

10

0

Ave

rage

stre

ss (M

Pa)

(b)

Figure 15 Loop strain development of specimen RS-B-2 with steel casing (a) Relationship of strain development with load (b) Relationshipof strain development with average stress

0 200 400 800600 1000

Concrete

1200 1400 1600 1800Strain (με)

500

600

700

800

400

300

200

100

0

Load

(kN

)

(a)

0 200 400 800600 1000

Concrete

1200 1400 1600 1800Strain (με)

30

35

40

25

20

15

5

10

0

Ave

rage

stre

ss (M

Pa)

(b)

Figure 16 Axial compressive strain development of core concrete of specimen RS-B-2

Advances in Materials Science and Engineering 11

strength of the concrete is converted into the steel thenominal compressive strength fcr of the steel is obtained andthe bearing capacity of the concrete-lled steel tubularmember is calculated from fcr fys is the yield limit of steel fckmeans the compressive strength of concrete cylinder As isthe cross-sectional area of steel pipe Ac is the cross-sectionalarea of concrete and λc is the ratio of slenderness toslenderness In Eurocode 4 (EC4) [22] the relative slen-derness λ for the plane of bending being considered is givenby λ

NPLRkNcrradic

where NplRk is the characteristic valueof the plastic resistance to compression if instead ofthe design strengths the characteristic values are used andNcr is the elastic critical normal force for the relevantbuckling mode calculated with the eective exuralstiness (EI)c

However it should be stated that the maximum allowablevalue of diameter-thickness ratio (Dt) specied in AISC [21]is 031lowast Efy the ratio of diameter-thickness of circular-section concrete-lled steel tubular members specied inChinese specication [28] should be limited to the followingrange 20

235fy

radicleDtle 85

235fy

radic and Eurocode 4 (EC4)

[22] explicit limits the allowed Dt values in the Europeancontext to 90lowast 235fy e diameter-thickness ratio of thespecimens studied in this paper is very large exceeding theallowable range of the specications e paper attempts toestimate these specimens with large diameter-thickness ratioby using the above codes And the ultimate strength calcu-lation results of relevant specications are shown in Table 7Apparently it can be found that value of the ultimate load isgenerallymuch greater than the theoretical calculation results

25

25

20

20

Z1P1Z1P2

Load

(kN

) 15

15

10

10

5

50

0Vertical displacement (mm)

(a)

Z2P2Z2P1

25

30

20

Load

(kN

)

15

10

5

025 30 3520151050

Vertical displacement (mm)

(b)

Z3P2Z3P1

30

40

20

Load

(kN

)

10

025 30 352015

Vertical displacement (mm)1050

(c)

Figure 17 Relationship of vertical displacement and load of three depths of rock-socketed columns (a) Rock-socketed depth is 300mm (P1steel tube is 1mm P2 steel tube is 0mm) (b) Rock-socketed depth is 400mm (c) Rock-socketed depth is 500mm

12 Advances in Materials Science and Engineering

AISC [21] method

Em Es + 04EcAc

As

fmy fys + 085fckAc

As

fcr 0658λ2c( )fmy if λc le 15

fcr 0877λ2c

fmy if λc le 15

λc lcrcπ

fmy

Em( )

05

NplRd 085Asfcr

(1)

EC4 and NBR 8800 [23 24] methods

NplRd η2Asfy + Acfck 1 + η1tfy

Dfck( ) (2)

η1 η10η2 η20

(3)

η10 49minus 185 times λ + 17(λ)2 ge 0 (4)

η20 025(3 + 2λ)le 10 (5)

GB50396-2014 [25] method

N0 Ascfsc

fsc 1212 + Bθ + Cθ2( )fc

αsc As

Ac

θ αscf

fc

(6)

5 Conclusion

e present study is an attempt to study the behavior ofconcrete-lled steel tube columns subjected to axialcompression Based on the results of this study the fol-lowing conclusions can be drawn within the scope of thesetests

Table 7 e ultimate strength calculation results of relevant specications

Specimens Ultimate load (kN) NBR 8800 and EC4 (kN) AISC (kN) GB50396-2014 (kN)PL-2 406 412 419 429NS-A-2 830 493 479 560NS-B-2 885 566 535 603RN-2 560 430 416 465RS-A-2 895 493 479 596RS-B-2 1190 566 535 639PL-1 480 513 519 530NS-A-1 800 428 409 478RS-A-1 895 428 409 478RS-B-1 1125 452 474 498

35

40

45

30Load

(kN

)25

2030 35 40 45 50 55

n

P1P2

Figure 18 Relationship between n and load (n ratio of rock-socketed depth n hD)

Advances in Materials Science and Engineering 13

(1) +e reinforced CFST piles exhibit two differentfailure modes When the weld strength of the steelcasing is greater than the axial load limit of thecomposite member the failure mode is the bendingfailure caused by the local buckling deformationwhich is a ductile failure feature When the weldstrength of the steel casing is less than the axial loadlimit of the composite member the failure mode isthe open splitting of the steel casing weld under theexpansion stress of the concrete which is a brittlefailure feature

(2) +e bearing capacity of rock-socketed CFSTcolumnsis lower than that of rock-socketed columns withouta steel tube under the same conditions of a verticalload +e depth of the rock inlay is clearly affectingby the bearing capacity of the two rock-socketedcolumns and the greater the rock-socketed depththe greater the bearing capacity of the rock-socketedpiles In addition the overall sliding of the steel tubeand the core concrete of pile is small and the steeltube-concrete interface is basically in a bonding stateunder the vertical load

(3) A comparison of failure loads between the tests andthe design codes was presented+e results show thatthe provisions in EC4 [22] NBR 8800 [23 24] AISC[21] and GB50396-2014 [25]conservatively estimatethe ultimate capacities of the specimens and it can befound that value of the ultimate load is generallymuch greater than the theoretical calculation resultsSince the diameter-thickness ratio of the specimensstudied in this paper is very large exceeding theallowable range of the specifications the test resultsprovide a reference for design and performance ofthe new structure with large diameter-thicknessratio

Data Availability

+e figures and tables data used to support the findings ofthis study are included within the article

Conflicts of Interest

+e authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

+is study was financially supported by the National NaturalScience Foundation of China (nos 2011550031 and51709026) and the Western Project of China (nos2011660041 and 2011560076)

References

[1] S Jegadesh and S Jayalekshmi ldquoLoad-bearing capacity ofaxially loaded circular concrete-filled steel tubular columnsrdquoProceedings of the Institution of Civil Engineers Structures andBuildings vol 169 no 7 pp 508ndash523 2016

[2] N E Shanmugam and B Lakshmi ldquoState of the art report onsteelndashconcrete composite columnsrdquo Journal of ConstructionalResearch vol 57 no 10 pp 1041ndash1080 2001

[3] S De Nardin ldquoeoretical-experimental study high strengthconcrete-filled steel tubesrdquo MS thesis EESC-USP Sao Carlos-SP 1999 in Portuguese

[4] K Cederwall B Engstrom and M Grauers ldquoHigh-strengthconcrete used in composite columnsrdquo in Proceedings of High-Strength Concretendash2nd International Symposium pp 195ndash214Detroit MI USA 1990

[5] L Han W Li and R Bjorhovde ldquoDevelopments and ad-vanced applications of concrete-filled steel tubular (CFST)structures membersrdquo Journal of Constructional Steel Re-search vol 100 pp 211ndash228 2014

[6] L Han H Shan-Hu and F Liao ldquoPerformance and calcu-lations of concrete filled steel tubes (CFST) under axialtensionrdquo Journal of Constructional Steel Research vol 67no 11 pp 1699ndash1709 2011

[7] M A Bradford ldquoDesign strength of slender concrete filledrectangular steel tubesrdquo ACI Structural Journal vol 93 no 2pp 229ndash235 1996

[8] M D OrsquoShea and R Q Bridge ldquoDesign of thin-walledconcrete filled steel tubesrdquo Journal of Structural Engineer-ing vol 126 no 11 pp 1295ndash1303 2000

[9] B Uy ldquoLocal and postlocal buckling of fabricated steel andcomposite cross sectionsrdquo Journal of Structural Engineeringvol 127 no 6 pp 666ndash677 2001

[10] K K Choi and Y Xiao ldquoAnalytical studies of concrete-filledcircular steel tubes under axial compressionrdquo Journal ofStructural Engineering vol 136 no 5 pp 565ndash573 2010

[11] Z Ou B Chen K H Hsieh M W Halling and P J BarrldquoExperimental and analytical investigation of concrete filledsteel tubular columnsrdquo Journal of Structural Engineeringvol 137 no 6 pp 635ndash645 2011

[12] T Perea R T Leon J F Hajjar and M D Denavit ldquoFull-scale tests of slender concrete-filled tubes axial behaviorrdquoJournal of Structural Engineering vol 139 no 7 pp 1249ndash1262 2013

[13] L H Han ldquoFlexural behavior of concrete-filled steel tubesrdquoJournal of Constructional Steel Research vol 60 no 2pp 313ndash337 2004

[14] L H Han ldquoFurther study on the flexural behavior ofconcrete-filled steel tubesrdquo Journal of Constructional SteelResearch vol 62 no 6 pp 554ndash565 2006

[15] H Lu L H Han and X L Zhao ldquoAnalytical behavior ofcircular concrete-filled thin-walled steel tubes subjected tobendingrdquoin-Walled Structures vol 47 no 3 pp 346ndash3582009

[16] C W Roeder D E Lehman and E Bishop ldquoStrength andstiffness of circular concrete-filled tubesrdquo Journal of StructuralEngineering vol 136 no 12 pp 1545ndash1553 2010

[17] J Moon C W Roeder D E Lehman and H Lee ldquoAnalyticalmodeling of bending of circular concrete-filled steel tubesrdquoEngineering Structures vol 42 pp 349ndash361 2012

[18] L H Han G H Yao and Z Tao ldquoPerformance of concrete-filled thin-walled steel tubes under pure torsionrdquoin-WalledStructures vol 45 no 1 pp 24ndash36 2007

[19] J Nie Y Wang and J Fan ldquoExperimental study on seismicbehavior of concrete filled steel tube columns under puretorsion and compressionndashtorsion cyclic loadrdquo Journal ofConstructional Steel Research vol 79 no 12 pp 115ndash1262013

[20] Y Wang J Nie and J Fan ldquo+eoretical model and in-vestigation of concrete filled steel tube columns under axial

14 Advances in Materials Science and Engineering

forcendashtorsion combined actionrdquo in-Walled Structuresvol 69 no 1 pp 1ndash9 2013

[21] American Institute of Steel Construction AISCndashLRFD MetricLoad and Resistance Factor Design Specification for StructuralSteel Buildings AISC Chicago IL USA 1994

[22] Europe en Comite de Normalisation ENV 1994ndash1ndash1 Euro-code 4mdashDesign of Composite Steel and Concrete StructuresPart 11 General Rules and Rules for Buildings CEN BrusselsBelgium 1994

[23] Brazilian Society of Standard Codes NBR 8800 Design andConstructional Details of Steel Structures of Buildings Bra-zilian Society of Standard Codes Rio de Janeiro Brazil 1986

[24] Brazilian Society of Standard Codes NBR 8800 BrazilianStandard Code Review Design and Constructional Details ofSteel and Composite Structures of Buildings BSSC BeloHorizonte Brazil 2003

[25] National Standards of the Peoplersquos Republic of China GB50936 Technical Code for Concrete Filled Steel TubularStructures National Standards of the Peoplersquos Republic ofChina Beijing China 2014 in Chinese

[26] Q Liu D Wang R Huang et al ldquoStudy on failure mode ofinland river large water level dock under ship impactrdquo PortEngineering Technology vol 47 no 4 2010 in Chinese

[27] J Xu ldquoStructural design of overhead vertical wharf for inlandriver large water levelrdquo Water Transport Engineeringvol 2006 pp 62ndash67 2006 in Chinese

[28] China Association for Engineering Construction Standardi-zation CECS 2890 Specification for Design and Constructionof Concrete-Filled Steel Tubular Structures China Associationfor Engineering Construction Standardization BeijingChina 2012 in Chinese

Advances in Materials Science and Engineering 15

CorrosionInternational Journal of

Hindawiwwwhindawicom Volume 2018

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Materials Science and EngineeringHindawiwwwhindawicom Volume 2018

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Analytical ChemistryInternational Journal of

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BioMed Research InternationalMaterials

Journal of

Hindawiwwwhindawicom Volume 2018

Na

nom

ate

ria

ls

Hindawiwwwhindawicom Volume 2018

Journal ofNanomaterials

Submit your manuscripts atwwwhindawicom

concrete and the strain of the concrete wasmeasuredwith thechange in the load In these tests each strain gauge was di-vided into vertical and horizontal measuring points therefore12 strain gauges a total of 24 points were placed on theoutside of each specimen Additionally four displacementgauges are arranged symmetrically on the pile top and the pilebottom to measure the change in the compression of the pilewith the load during the loading process these results wereused as the basis of the loading control method

22 Columns with Foundation

221 Test Program +e test program for the columns withfoundation is approximately consistent with that of the

concrete-filled steel tube columns without foundation thecross sections of these columns are also circular and all thecolumns were filled with C30 concrete +e specimens weretested and a summary of their properties is presented inTable 5 +e length of each column specimen is 800mm thediameter of each is 100mm and the size of foundation is21mtimes 13mtimes 1m

222 Properties of the Materials +e concrete for thecolumns was produced with high-strength M30 cementmortar with a cement quartz sand water mix ratio of 1 176 032 (mass ratio) +e diameter of the steel tube is100mm its thickness is 1mm and its elastic modulus isapproximately E 200GPa Additionally the main bar ofsecondary reinforcement has a diameter of 6mm and thestirrups have a diameter of 1mm +e stirrups spacing is3 cm in the column

Due to the large size of the test foundations they cannotbe excavated to the laboratory so concrete was used tosimulate the rock foundation Mudstone is susceptible toweathering which leads to a reduction in the bearing ca-pacity of the pile therefore the concrete strength is low tosimulate strong weathering mudstones +e concrete mixratio is 125 cementitious material 125 stone and 50sand After 28 days of curing testing results showed that thecompressive strength of the standard concrete was 300KPaand the elastic modulus was 16MPa

+e pile was formed as shown in Figure 3 In additionthe material properties of the concrete core and steel tube areshown in Table 6

223 Test Setup +e loading system uses a split hydraulicjack with a limit load of 200 kN When the loading device isinstalled the load sensor can be placed on a piece of steelplate on top of the pile and the loading apparatus isa separate hydraulic jack that is placed on top +e top of the

Table 1 List of columns for CFST columns without foundation

Specimens D times δ times L

(mm)

Ac(mm2)

Ar(mm2)

As(mm2)αsc()

PL-2 165times 0times1200 21382 0 0 0NS-A-2 165times12times1200 21382 0 622 29NS-B-2 165times16times1200 21382 0 829 39RN-2 165times 0times1200 21382 170 0 08RS-A-2 165times12times1200 21382 170 622 37RS-B-2 165times16times1200 21382 170 829 47PL-1 150times 0times1200 17671 0 0 0NS-A-1 150times12times1200 17671 0 570 32RS-A-1 150times12times1200 17671 170 570 41RS-B-1 150times16times1200 17671 170 762 52Notation D outside diameter of the circular steel tube δ wall thickness ofthe steel tube L length of the specimens Ac concrete cross-sectional areaAr reinforced cross-sectional area As steel cross-sectional area αsc steelratio PL plain concrete RS concrete-filled steel tube column with rein-forcing bars NS concrete-filled steel tube column without reinforcing barsand RN concrete column with reinforcing bars A thickness of steel tube is12mm B thickness of steel tube is 16mm 1 diameter is 150mm 2diameter is 165mm

Φ250Outer stirrups

5Φ6

Φ(12) t(AB)Steel tube

Φ2100Inner stirrups R

300

300

300

300

L=

1200

Strain gauges

Figure 1 Schematic of the specimens and arrangement of thestrain gauges around the columns

Table 2 Concrete mix ratio

Grade Concrete mixratio

Cement(kgm3)

Water(kgm3)

Stone(kgm3)

Sand(kgm)

C30 065 300 195 1220 685

Table 3 Mechanical properties of the concrete and steel tube

Specimens fcu (MPa) fy (MPa)PL-2 321 mdashNS-A-2 346 375NS-B-2 349 375RN-2 312 375RS-A-2 337 375RS-B-2 335 375PL-1 348 mdashNS-A-1 329 375RS-A-1 334 375RS-B-1 341 375

Table 4 Material properties of the concrete and steel tube

Types Grade E (MPa) ΝConcrete C30 275E+ 04 02Reinforcement HRB335 210E+ 05 03Steel HRB335 210E+ 05 03Stirrups HRB335 210E+ 05 03

Advances in Materials Science and Engineering 3

(a) (b)

Figure 2 Test setup (a) General view (b) CFST detail

Table 5 List of columns for CFST columns with foundation

Specimens D (mm) h (mm) n (n hD) Steel tube (mm)Z1P1 100 300 3 1Z1P2 100 300 3 0Z2P1 100 400 4 1Z2P2 100 400 4 0Z3P1 100 500 5 1Z3P2 100 500 5 0Notation Z1 rock-socketed depth is 300mm Z2 rock-socketed depth is 400mm Z3 rock-socketed depth is 500mm P1 steel tube is 1mm P2 steel tube is0mm h rock-socketed depth n ratio of rock-socketed depth n hD

(a) (b)

Figure 3 Properties of the materials (a) General prefabricated piles (b) Steel tube prefabricated piles

4 Advances in Materials Science and Engineering

jack is xed to the reaction beam and the device diagram isshown in Figure 4 During step-by-step loading to keep eachload the same the load is calculated according to 10 of theestimated carrying capacitye rst stage load is 2 times thegrading load the unloading is reduced by a consistent 20 ofthe carrying capacity e requirements are that thetransmission load is uniform continuous and stable andthat the time of loading is at least 1 minute

3 Test Results and Discussion

31 Columns without Foundation

311 Failure Modes e typical failure modes of thespecimens in this test are as followse failure modes of theplain concrete specimen (PL-2) and the reinforced concretespecimen (RN-2) are shown in Figures 5(a) and 5(b) emain failure mode is the fracture of the top concrete and thecrushing range is about one quarter of the length of the pile

e typical failure mode of the unreinforced CFSTspecimens (NS-A-2 and NS-B-2) is shown in Figure 5(c)which is mainly represented by the local buckling of thespecimen after concrete crushing

e reinforced CFST piles exhibit two dierent failuremodes e specimens with the thickness of 16mm of steelcasing (RS-B-1 and RS-B-2) locally exhibit buckling de-formation during loading the local deformation is graduallyincreased with the loading and the specimen is bent anddeformed until the bearing capacity is nally lost as shownin Figure 6(a) e specimens with the thickness of 12mm(RS-A-1 and RS-A-2) showed the same deformation char-acteristics as the specimen RS-B-1 in the early stage ofloading but when the load reaches 850 kN the weld of thesteel casing suddenly opened e specimen is destroyedinstantaneously as shown in Figure 6(b) In summary twodierent types of damage may occur in reinforced CFSTwhen axially compressed

(1) When the weld strength of the steel casing is greaterthan the axial load limit of the composite memberthe failure mode is the bending failure caused by thelocal buckling deformation which is a ductile failurefeature

(2) When the weld strength of the steel casing is less thanthe axial load limit of the composite member thefailure mode is the open splitting of the steel casingweld under the expansion stress of the concretewhich is a brittle failure feature

312 Load-Displacement Curve

(1) Reinforced and Unreinforced CFST Members e load-vertical displacement curves of reinforced CFST specimenswith steel casing thickness of 12mm (RS-A-2) and 16mm(RS-B-2) are shown in Figure 7 It can be seen from the testresults that when the thickness of the steel casing increases to16mm the displacement of the top of the specimen with theload is the same as that of the thickness of 12mm and bothexhibit obvious plastic failure properties the proportionallimit of two thicknesses is relatively close which is ap-proximately 600 kN Before the load reaches 600 kN theload-displacement curves of the two test pieces are basicallycoincident When the load exceeds 600 kN that is afterentering the plastic zone the absolute value of the dis-placement increment under the same load increment issmaller than the case where the thickness of the steel casingis 12mm under the same condition It indicates that therestraining eect of the steel casing on the core concrete ismainly reected in the plastic zone of the component whilethe eect on the elastic zone is small e maximum dis-placement that can be achieved with a thickness of 16mm is138mm which is greatly improved compared to thethickness of the steel casing of 12mm erefore thethickness of the steel casing has a great inuence on theductility of the reinforcing member and the improvement ofits bearing capacity

e load-vertical displacement curves of CFST speci-mens with steel tube thickness is 12mm (RS-A-2 and NS-A-2) and t steel tube thickness is 16mm (RS-B-2 and NS-B-2)composite members are shown in Figures 8 and 9

Steel tubeP1P2

Foundation21m times 13m times 1m

Hydraulic jacks

Load cell Displacement meter

L=

800m

m

h

Figure 4 Test setup (hmeans rock-socketed depth P1 steel tube is1mm P2 steel tube is 0mm)

Table 6 Material properties of the concrete core and steel tube

Steel tube Concrete Reinforcedbar

Steel tube(mm)

D 100mm M30 D 6mm Ec 16MPat 1mm mdash mdash fy 300KPa

Es 200GPaC S W 1 176

032 mdash mdash

Advances in Materials Science and Engineering 5

It can be obtained from the test results that the pro-portional limit of the load-vertical displacement curve ofreinforced CFST piles is slightly higher than unreinforcedones and the proportional limit of the specimen RS-A-2 andRS-B-2 is about 600 kN greater than 500 kN of test NS-A-2and NS-B-2 At the same time the ultimate deformationcapacity of reinforced CFST composite members is betterthan that of unreinforced CFST specimens It can be seenthat in the elastic stress stage the presence of the stressedsteel bars delays the generation of concrete cracks therebyincreasing the proportional limit of the test In the plasticstage the stressed steel bars play a further restraining roleon the core concrete which inhibits the formation and

expansion of the crack and improves the ductility and ul-timate deformation ability of the test

(2) Encased and Nonencased Members +e load-verticaldisplacement curves of plain concrete specimen (PL-2)and reinforced concrete specimen (RN-2) and reinforcedCFST composite members (RS-A-2 and RS-B-2) are shownin Figure 10 It can be seen from the test results that the steeltube has a great influence on the bearing capacity and de-formation capacity of the test For the plain concretespecimen (PL-2) the ultimate bearing capacity and ultimatedeformation are small and the maximum displacement is287mm showing the characteristics of brittle failure For the

(a) (b)

(c)

Figure 5 Failure modes (a) Plain concrete pile (b) Reinforced concrete pile (c) Unreinforced CFST pile

6 Advances in Materials Science and Engineering

reinforced concrete specimen (RN-2) the load-displacementcurve shows a certain ductility characteristic but the ultimatebearing capacity and ultimate deformation of the specimenare signicantly smaller than the reinforced CFST compositemember

313 Strain Development In this paper the strain law of thesteel casing and concrete core under the condition of an axialcompression load is described for the specimens with a steeltube thickness of 12mm (specimen RS-A-2) and 16mm(specimen RS-B-2) During the test the vertical strain andhoop strain on the side of the steel casing were monitoredand the development rule of the compressive strain inside

the core concrete was monitored Among them four straingauges are arranged on the side of the steel casing at the topandmiddle and top of the test specimen in the circumferentialdirection and the vertical strain and lateral strain of the steelcasing at this position are measured respectively In the dataprocessing the strain values of four measuring points in thesame plane are averaged to obtain the average strain of thesteel casing at the plane e load-strain curve and averagestress-strain curve of the test piece are given below Amongthem the average stress is obtained by dividing the axial loadon the specimen by the cross-sectional area

e developments of the longitudinal strain circum-ferential strain and compression behavior of the steel tubeare shown in Figures 11ndash16 Figures 11ndash13 are laws of strain

(a) (b)

Figure 6 Failure modes of reinforced CFST pile (a) Buckling deformation (b) Splitting of the steel casing weld

1200

1000

800

600

400

200

00 2 4 6 8 10 12

RS-A-2RS-B-2

14Vertical displacement (mm)

Load

(kN

)

Figure 7 Vertical displacement-load curves of two thickness steeltube-reinforced CFST piles

1000

800

600

400

200

00 2 4 6 8 10 12

RS-A-2NS-A-2

14Vertical displacement (mm)

Load

(kN

)

Figure 8 Comparison of reinforced and unreinforced CFST pileswith thickness is 12mm

Advances in Materials Science and Engineering 7

development of specimen RS-A-2 and Figures 14ndash16 arelaws of strain development of specimen RS-B-2

From the above test results it can be seen that for thesteel casing-reinforced concrete composite member thestrain value in the middle of the specimen is slightly largerthan the top and bottom strain values e strain devel-opment of steel casings at each measuring point showselastic-plastic characteristics with the increase of load Be-fore the axial load value is less than 045 times the ultimateload of the model pile foundation the load and strain showa linear relationship while the load reaches 045 times theultimate load carrying capacity After the capacity under thesame load increment the strain increment gradually in-creases showing a nonlinear characteristic From the wholeload-strain curves of the reinforced CFST specimens itexhibited the characteristics of ductile failure

In summary the use of a steel tube plays a very im-portant role in improving the compressive deformation andmechanical properties of the components For a joint steeltube-reinforced concrete structure the bearing capacity andthe ductility of the components are greatly improvedcompared to the specimens with no steel which is due to theexistence of the internal structure of the composite structureeectively enhancing the constraints between the concreteparticles to limit the development of microcracks and theeective stress

32 Columnswith Foundation It can be seen from Figure 17that the variation in the results of the dierent model col-umns under the load at the pile top is consistent and it canbe considered that the inuence of a rockless cylinder on the

1200

1000

800

600

400

200

00 2 4 6 8 10 12

RS-B-2NS-B-2

14Vertical displacement (mm)

Load

(kN

)

Figure 9 Comparison of reinforced and unreinforced CFST piles with thickness is 16mm

1000

800

600

400

200

00 2 4 6 8 10 12

RS-A-2PL-2RN-2

14Vertical displacement (mm)

Load

(kN

)

(a)

1200

1000

800

600

400

200

00 2 4 6 8 10 12 14

Vertical displacement (mm)

Load

(kN

)

RS-B-2PL-2RN-2

(b)

Figure 10 Comparison of plain concrete reinforced concrete and reinforced CFST piles

8 Advances in Materials Science and Engineering

settlement of a rock-socketed column is also consistent Itcan be seen from Figure 17 that the displacements of Z1P1and Z1P2 are basically the same from the load values of zeroto 9 kN the load-vertical displacement curve is approxi-mately a straight line and the two piles are in the elasticstage After the load exceeds 9 kN the displacement rate ofthe Z1P1 pile exceeds that of the Z1P2 pile and the settle-ment of the pile top increases e load-vertical displace-ment curves of the two piles change slowly and the processof steep drop is not obvious Figure 17 shows several settlingsthat may be due to the inhomogeneity of the model

foundation According to the above analysis it can be seenthat the vertical bearing capacities of CFST rock-socketedpiles are weaker than those rock-socketed piles withouta steel tube the dierence is mainly because the rock-socketed pile without a steel tube has a concrete-rock in-terface with a coecurrencient of friction greater than that of theCFST rock-socketed pile with a steel-rock interface

As seen from Figure 18 the greater the rock-socketeddepth the greater the load-bearing capacity of the rock-socketed piles In addition when the depth of the pile in therock-socketed increased from 3D to 5D the vertical ultimate

1000

800

600

400

200

00 2000 4000 6000

Strain (με)8000 10000 12000

Top verticalBottom verticalCentral vertical

Load

(kN

)

(a)

50

40

30

20

Ave

rage

stre

ss (M

Pa)

10

0

Strain (με)2000

Top verticalBottom verticalCentral vertical

4000 6000 8000 10000 120000

(b)

Figure 11 Vertical strain development laws of specimen RS-A-2 with steel casing (a) Relationship of vertical strain development with load(b) Relationship of vertical strain development with average stress

1000

800

600

400

200

0 1000 2000 3000Strain (με)

4000 5000 6000 7000 8000

Load

(kN

)

Top loopBottom loopCentral loop

0

(a)

50

40

30

20

10

00 1000 2000 40003000

Strain (με)5000 6000 7000 8000

Ave

rage

stre

ss (M

Pa)

Top loopBottom loopCentral loop

(b)

Figure 12 Loop strain development of specimen RS-A-2 with steel casing (a) Relationship of loop strain development with load (b)Relationship of loop strain development with average stress

Advances in Materials Science and Engineering 9

bearing capacity increased by approximately 40 e mainreason for this eect is that with the increase in the rock-socketed depth the contact area will increase and althoughthe side friction coecurrencient does not change the total frictionof the pile will signicantly increase therefore the verticalbearing capacity of the pile is signicantly improved It isfound that the vertical ultimate bearing capacity of rock-socketed piles without a steel tube (steel-free cylinder) isapproximately 10 higher than that of the steel-retainingtube when the depth of rock-embedment is the same emain reason for this phenomenon is that the outer wall ofthe pile is very smooth since its roughness is much smallerthan the concrete the corresponding side friction is lower

and the ultimate bearing capacity of the pile is equal to thepile side friction and pile end resistance decreasing theultimate bearing capacity of the pile

4 Analysis of the Ultimate Load

According to EC4 [22] the axial load capacity (NplRd) ofa CFST column can be determined by summing the yieldload of both the steel section and concrete core Forconcrete-ned tubes of circular cross section account maybe taken of increase in strength of concrete caused byconnement provided that the relative slenderness λ doesnot exceed 0 5 and edlt 0 1 where e is the eccentricity of

0 200 400 800600 1000

Concrete

1200 1400 1600Strain (με)

500

600

700

400

300

200

100

0

Load

(kN

)

(a)

Concrete

0 200 400 800600 1000 1200 1400 1600Strain (με)

30

35

25

20

15

5

10

0

Ave

rage

stre

ss (M

Pa)

(b)

Figure 13 Axial compressive strain development of core concrete of specimen RS-A-2 (a) Relationship of vertical strain development withload (b) Relationship of vertical strain development with average stress

0 2000 4000 80006000Strain (με)

10000 12000 14000

Top vertical

Bottom verticalCentral vertical

1000

1200

800

600

400

200

0

Load

(kN

)

(a)

0 2000 4000 80006000Strain (με)

10000 12000 14000

Top verticalMiddle verticalBottom vertical

50

60

40

30

20

10

0

Ave

rage

stre

ss (M

Pa)

(b)

Figure 14 Vertical strain development laws of specimen RS-B-2 with steel casing (a) Relationship of loop strain development with load (b)Relationship of loop strain development with average stress

10 Advances in Materials Science and Engineering

loading given by MEdNEd and d is the external diameter ofthe column e plastic resistance to compression may thenbe calculated from the following expression in equations(2)ndash(5) e application of EC4 [22] is restricted to com-posite columns with steel yield stress and concrete cylinderstrength of less than 355 and 50MPa respectively efollowing presents the formulations of the AISC [21] EC4[22] NBR 8800 [23 24] and GB50396-2014 [25] standardcodes to determine the resistance capacity of axially loadedCFST columns And rs is the radius of gyration of the steelhollow section le is the length of the column Ec is themodulus of elasticity of the concrete and Es is the modulusof elasticity of the steel e formulations presented were

used to calculate the compressive strength of the axiallyloaded CFST columns investigated in the present study Inaddition the boundary conditions of the testing approachare upper if the pile is loading and lower if the pile is xed

In GB50396-2014 [25] θ means the hoop coecurrencient ofconcrete-lled steel tubular members θ αscffc αsc rep-resents the steel content of concrete-lled steel tubularmembers in the design of compressive strength of concrete-lled steel tube piles B and C are the inuence factors of thecross-sectional shape on the hoop eect and about circularcross section B 0176lowast f213 + 0974 Cminus0104fc144+ 0031 In AISC [21] the axial compression member isconsidered to be the overall stability of the member the

0 1000 2000 40003000Strain (με)

5000 6000 7000

Top loopCentral loopBottom loop

1000

1200

800

600

400

200

0

Load

(kN

)

(a)

0 1000 2000 40003000Strain (με)

5000 6000 7000

Top loopCentral loopBottom loop

50

60

40

30

20

10

0

Ave

rage

stre

ss (M

Pa)

(b)

Figure 15 Loop strain development of specimen RS-B-2 with steel casing (a) Relationship of strain development with load (b) Relationshipof strain development with average stress

0 200 400 800600 1000

Concrete

1200 1400 1600 1800Strain (με)

500

600

700

800

400

300

200

100

0

Load

(kN

)

(a)

0 200 400 800600 1000

Concrete

1200 1400 1600 1800Strain (με)

30

35

40

25

20

15

5

10

0

Ave

rage

stre

ss (M

Pa)

(b)

Figure 16 Axial compressive strain development of core concrete of specimen RS-B-2

Advances in Materials Science and Engineering 11

strength of the concrete is converted into the steel thenominal compressive strength fcr of the steel is obtained andthe bearing capacity of the concrete-lled steel tubularmember is calculated from fcr fys is the yield limit of steel fckmeans the compressive strength of concrete cylinder As isthe cross-sectional area of steel pipe Ac is the cross-sectionalarea of concrete and λc is the ratio of slenderness toslenderness In Eurocode 4 (EC4) [22] the relative slen-derness λ for the plane of bending being considered is givenby λ

NPLRkNcrradic

where NplRk is the characteristic valueof the plastic resistance to compression if instead ofthe design strengths the characteristic values are used andNcr is the elastic critical normal force for the relevantbuckling mode calculated with the eective exuralstiness (EI)c

However it should be stated that the maximum allowablevalue of diameter-thickness ratio (Dt) specied in AISC [21]is 031lowast Efy the ratio of diameter-thickness of circular-section concrete-lled steel tubular members specied inChinese specication [28] should be limited to the followingrange 20

235fy

radicleDtle 85

235fy

radic and Eurocode 4 (EC4)

[22] explicit limits the allowed Dt values in the Europeancontext to 90lowast 235fy e diameter-thickness ratio of thespecimens studied in this paper is very large exceeding theallowable range of the specications e paper attempts toestimate these specimens with large diameter-thickness ratioby using the above codes And the ultimate strength calcu-lation results of relevant specications are shown in Table 7Apparently it can be found that value of the ultimate load isgenerallymuch greater than the theoretical calculation results

25

25

20

20

Z1P1Z1P2

Load

(kN

) 15

15

10

10

5

50

0Vertical displacement (mm)

(a)

Z2P2Z2P1

25

30

20

Load

(kN

)

15

10

5

025 30 3520151050

Vertical displacement (mm)

(b)

Z3P2Z3P1

30

40

20

Load

(kN

)

10

025 30 352015

Vertical displacement (mm)1050

(c)

Figure 17 Relationship of vertical displacement and load of three depths of rock-socketed columns (a) Rock-socketed depth is 300mm (P1steel tube is 1mm P2 steel tube is 0mm) (b) Rock-socketed depth is 400mm (c) Rock-socketed depth is 500mm

12 Advances in Materials Science and Engineering

AISC [21] method

Em Es + 04EcAc

As

fmy fys + 085fckAc

As

fcr 0658λ2c( )fmy if λc le 15

fcr 0877λ2c

fmy if λc le 15

λc lcrcπ

fmy

Em( )

05

NplRd 085Asfcr

(1)

EC4 and NBR 8800 [23 24] methods

NplRd η2Asfy + Acfck 1 + η1tfy

Dfck( ) (2)

η1 η10η2 η20

(3)

η10 49minus 185 times λ + 17(λ)2 ge 0 (4)

η20 025(3 + 2λ)le 10 (5)

GB50396-2014 [25] method

N0 Ascfsc

fsc 1212 + Bθ + Cθ2( )fc

αsc As

Ac

θ αscf

fc

(6)

5 Conclusion

e present study is an attempt to study the behavior ofconcrete-lled steel tube columns subjected to axialcompression Based on the results of this study the fol-lowing conclusions can be drawn within the scope of thesetests

Table 7 e ultimate strength calculation results of relevant specications

Specimens Ultimate load (kN) NBR 8800 and EC4 (kN) AISC (kN) GB50396-2014 (kN)PL-2 406 412 419 429NS-A-2 830 493 479 560NS-B-2 885 566 535 603RN-2 560 430 416 465RS-A-2 895 493 479 596RS-B-2 1190 566 535 639PL-1 480 513 519 530NS-A-1 800 428 409 478RS-A-1 895 428 409 478RS-B-1 1125 452 474 498

35

40

45

30Load

(kN

)25

2030 35 40 45 50 55

n

P1P2

Figure 18 Relationship between n and load (n ratio of rock-socketed depth n hD)

Advances in Materials Science and Engineering 13

(1) +e reinforced CFST piles exhibit two differentfailure modes When the weld strength of the steelcasing is greater than the axial load limit of thecomposite member the failure mode is the bendingfailure caused by the local buckling deformationwhich is a ductile failure feature When the weldstrength of the steel casing is less than the axial loadlimit of the composite member the failure mode isthe open splitting of the steel casing weld under theexpansion stress of the concrete which is a brittlefailure feature

(2) +e bearing capacity of rock-socketed CFSTcolumnsis lower than that of rock-socketed columns withouta steel tube under the same conditions of a verticalload +e depth of the rock inlay is clearly affectingby the bearing capacity of the two rock-socketedcolumns and the greater the rock-socketed depththe greater the bearing capacity of the rock-socketedpiles In addition the overall sliding of the steel tubeand the core concrete of pile is small and the steeltube-concrete interface is basically in a bonding stateunder the vertical load

(3) A comparison of failure loads between the tests andthe design codes was presented+e results show thatthe provisions in EC4 [22] NBR 8800 [23 24] AISC[21] and GB50396-2014 [25]conservatively estimatethe ultimate capacities of the specimens and it can befound that value of the ultimate load is generallymuch greater than the theoretical calculation resultsSince the diameter-thickness ratio of the specimensstudied in this paper is very large exceeding theallowable range of the specifications the test resultsprovide a reference for design and performance ofthe new structure with large diameter-thicknessratio

Data Availability

+e figures and tables data used to support the findings ofthis study are included within the article

Conflicts of Interest

+e authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

+is study was financially supported by the National NaturalScience Foundation of China (nos 2011550031 and51709026) and the Western Project of China (nos2011660041 and 2011560076)

References

[1] S Jegadesh and S Jayalekshmi ldquoLoad-bearing capacity ofaxially loaded circular concrete-filled steel tubular columnsrdquoProceedings of the Institution of Civil Engineers Structures andBuildings vol 169 no 7 pp 508ndash523 2016

[2] N E Shanmugam and B Lakshmi ldquoState of the art report onsteelndashconcrete composite columnsrdquo Journal of ConstructionalResearch vol 57 no 10 pp 1041ndash1080 2001

[3] S De Nardin ldquoeoretical-experimental study high strengthconcrete-filled steel tubesrdquo MS thesis EESC-USP Sao Carlos-SP 1999 in Portuguese

[4] K Cederwall B Engstrom and M Grauers ldquoHigh-strengthconcrete used in composite columnsrdquo in Proceedings of High-Strength Concretendash2nd International Symposium pp 195ndash214Detroit MI USA 1990

[5] L Han W Li and R Bjorhovde ldquoDevelopments and ad-vanced applications of concrete-filled steel tubular (CFST)structures membersrdquo Journal of Constructional Steel Re-search vol 100 pp 211ndash228 2014

[6] L Han H Shan-Hu and F Liao ldquoPerformance and calcu-lations of concrete filled steel tubes (CFST) under axialtensionrdquo Journal of Constructional Steel Research vol 67no 11 pp 1699ndash1709 2011

[7] M A Bradford ldquoDesign strength of slender concrete filledrectangular steel tubesrdquo ACI Structural Journal vol 93 no 2pp 229ndash235 1996

[8] M D OrsquoShea and R Q Bridge ldquoDesign of thin-walledconcrete filled steel tubesrdquo Journal of Structural Engineer-ing vol 126 no 11 pp 1295ndash1303 2000

[9] B Uy ldquoLocal and postlocal buckling of fabricated steel andcomposite cross sectionsrdquo Journal of Structural Engineeringvol 127 no 6 pp 666ndash677 2001

[10] K K Choi and Y Xiao ldquoAnalytical studies of concrete-filledcircular steel tubes under axial compressionrdquo Journal ofStructural Engineering vol 136 no 5 pp 565ndash573 2010

[11] Z Ou B Chen K H Hsieh M W Halling and P J BarrldquoExperimental and analytical investigation of concrete filledsteel tubular columnsrdquo Journal of Structural Engineeringvol 137 no 6 pp 635ndash645 2011

[12] T Perea R T Leon J F Hajjar and M D Denavit ldquoFull-scale tests of slender concrete-filled tubes axial behaviorrdquoJournal of Structural Engineering vol 139 no 7 pp 1249ndash1262 2013

[13] L H Han ldquoFlexural behavior of concrete-filled steel tubesrdquoJournal of Constructional Steel Research vol 60 no 2pp 313ndash337 2004

[14] L H Han ldquoFurther study on the flexural behavior ofconcrete-filled steel tubesrdquo Journal of Constructional SteelResearch vol 62 no 6 pp 554ndash565 2006

[15] H Lu L H Han and X L Zhao ldquoAnalytical behavior ofcircular concrete-filled thin-walled steel tubes subjected tobendingrdquoin-Walled Structures vol 47 no 3 pp 346ndash3582009

[16] C W Roeder D E Lehman and E Bishop ldquoStrength andstiffness of circular concrete-filled tubesrdquo Journal of StructuralEngineering vol 136 no 12 pp 1545ndash1553 2010

[17] J Moon C W Roeder D E Lehman and H Lee ldquoAnalyticalmodeling of bending of circular concrete-filled steel tubesrdquoEngineering Structures vol 42 pp 349ndash361 2012

[18] L H Han G H Yao and Z Tao ldquoPerformance of concrete-filled thin-walled steel tubes under pure torsionrdquoin-WalledStructures vol 45 no 1 pp 24ndash36 2007

[19] J Nie Y Wang and J Fan ldquoExperimental study on seismicbehavior of concrete filled steel tube columns under puretorsion and compressionndashtorsion cyclic loadrdquo Journal ofConstructional Steel Research vol 79 no 12 pp 115ndash1262013

[20] Y Wang J Nie and J Fan ldquo+eoretical model and in-vestigation of concrete filled steel tube columns under axial

14 Advances in Materials Science and Engineering

forcendashtorsion combined actionrdquo in-Walled Structuresvol 69 no 1 pp 1ndash9 2013

[21] American Institute of Steel Construction AISCndashLRFD MetricLoad and Resistance Factor Design Specification for StructuralSteel Buildings AISC Chicago IL USA 1994

[22] Europe en Comite de Normalisation ENV 1994ndash1ndash1 Euro-code 4mdashDesign of Composite Steel and Concrete StructuresPart 11 General Rules and Rules for Buildings CEN BrusselsBelgium 1994

[23] Brazilian Society of Standard Codes NBR 8800 Design andConstructional Details of Steel Structures of Buildings Bra-zilian Society of Standard Codes Rio de Janeiro Brazil 1986

[24] Brazilian Society of Standard Codes NBR 8800 BrazilianStandard Code Review Design and Constructional Details ofSteel and Composite Structures of Buildings BSSC BeloHorizonte Brazil 2003

[25] National Standards of the Peoplersquos Republic of China GB50936 Technical Code for Concrete Filled Steel TubularStructures National Standards of the Peoplersquos Republic ofChina Beijing China 2014 in Chinese

[26] Q Liu D Wang R Huang et al ldquoStudy on failure mode ofinland river large water level dock under ship impactrdquo PortEngineering Technology vol 47 no 4 2010 in Chinese

[27] J Xu ldquoStructural design of overhead vertical wharf for inlandriver large water levelrdquo Water Transport Engineeringvol 2006 pp 62ndash67 2006 in Chinese

[28] China Association for Engineering Construction Standardi-zation CECS 2890 Specification for Design and Constructionof Concrete-Filled Steel Tubular Structures China Associationfor Engineering Construction Standardization BeijingChina 2012 in Chinese

Advances in Materials Science and Engineering 15

CorrosionInternational Journal of

Hindawiwwwhindawicom Volume 2018

Advances in

Materials Science and EngineeringHindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Journal of

Chemistry

Analytical ChemistryInternational Journal of

Hindawiwwwhindawicom Volume 2018

ScienticaHindawiwwwhindawicom Volume 2018

Polymer ScienceInternational Journal of

Hindawiwwwhindawicom Volume 2018

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Advances in Condensed Matter Physics

Hindawiwwwhindawicom Volume 2018

International Journal of

BiomaterialsHindawiwwwhindawicom

Journal ofEngineeringVolume 2018

Applied ChemistryJournal of

Hindawiwwwhindawicom Volume 2018

NanotechnologyHindawiwwwhindawicom Volume 2018

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Hindawiwwwhindawicom Volume 2018

High Energy PhysicsAdvances in

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom

The Scientific World Journal

Volume 2018

TribologyAdvances in

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

ChemistryAdvances in

Hindawiwwwhindawicom Volume 2018

Advances inPhysical Chemistry

Hindawiwwwhindawicom Volume 2018

BioMed Research InternationalMaterials

Journal of

Hindawiwwwhindawicom Volume 2018

Na

nom

ate

ria

ls

Hindawiwwwhindawicom Volume 2018

Journal ofNanomaterials

Submit your manuscripts atwwwhindawicom

(a) (b)

Figure 2 Test setup (a) General view (b) CFST detail

Table 5 List of columns for CFST columns with foundation

Specimens D (mm) h (mm) n (n hD) Steel tube (mm)Z1P1 100 300 3 1Z1P2 100 300 3 0Z2P1 100 400 4 1Z2P2 100 400 4 0Z3P1 100 500 5 1Z3P2 100 500 5 0Notation Z1 rock-socketed depth is 300mm Z2 rock-socketed depth is 400mm Z3 rock-socketed depth is 500mm P1 steel tube is 1mm P2 steel tube is0mm h rock-socketed depth n ratio of rock-socketed depth n hD

(a) (b)

Figure 3 Properties of the materials (a) General prefabricated piles (b) Steel tube prefabricated piles

4 Advances in Materials Science and Engineering

jack is xed to the reaction beam and the device diagram isshown in Figure 4 During step-by-step loading to keep eachload the same the load is calculated according to 10 of theestimated carrying capacitye rst stage load is 2 times thegrading load the unloading is reduced by a consistent 20 ofthe carrying capacity e requirements are that thetransmission load is uniform continuous and stable andthat the time of loading is at least 1 minute

3 Test Results and Discussion

31 Columns without Foundation

311 Failure Modes e typical failure modes of thespecimens in this test are as followse failure modes of theplain concrete specimen (PL-2) and the reinforced concretespecimen (RN-2) are shown in Figures 5(a) and 5(b) emain failure mode is the fracture of the top concrete and thecrushing range is about one quarter of the length of the pile

e typical failure mode of the unreinforced CFSTspecimens (NS-A-2 and NS-B-2) is shown in Figure 5(c)which is mainly represented by the local buckling of thespecimen after concrete crushing

e reinforced CFST piles exhibit two dierent failuremodes e specimens with the thickness of 16mm of steelcasing (RS-B-1 and RS-B-2) locally exhibit buckling de-formation during loading the local deformation is graduallyincreased with the loading and the specimen is bent anddeformed until the bearing capacity is nally lost as shownin Figure 6(a) e specimens with the thickness of 12mm(RS-A-1 and RS-A-2) showed the same deformation char-acteristics as the specimen RS-B-1 in the early stage ofloading but when the load reaches 850 kN the weld of thesteel casing suddenly opened e specimen is destroyedinstantaneously as shown in Figure 6(b) In summary twodierent types of damage may occur in reinforced CFSTwhen axially compressed

(1) When the weld strength of the steel casing is greaterthan the axial load limit of the composite memberthe failure mode is the bending failure caused by thelocal buckling deformation which is a ductile failurefeature

(2) When the weld strength of the steel casing is less thanthe axial load limit of the composite member thefailure mode is the open splitting of the steel casingweld under the expansion stress of the concretewhich is a brittle failure feature

312 Load-Displacement Curve

(1) Reinforced and Unreinforced CFST Members e load-vertical displacement curves of reinforced CFST specimenswith steel casing thickness of 12mm (RS-A-2) and 16mm(RS-B-2) are shown in Figure 7 It can be seen from the testresults that when the thickness of the steel casing increases to16mm the displacement of the top of the specimen with theload is the same as that of the thickness of 12mm and bothexhibit obvious plastic failure properties the proportionallimit of two thicknesses is relatively close which is ap-proximately 600 kN Before the load reaches 600 kN theload-displacement curves of the two test pieces are basicallycoincident When the load exceeds 600 kN that is afterentering the plastic zone the absolute value of the dis-placement increment under the same load increment issmaller than the case where the thickness of the steel casingis 12mm under the same condition It indicates that therestraining eect of the steel casing on the core concrete ismainly reected in the plastic zone of the component whilethe eect on the elastic zone is small e maximum dis-placement that can be achieved with a thickness of 16mm is138mm which is greatly improved compared to thethickness of the steel casing of 12mm erefore thethickness of the steel casing has a great inuence on theductility of the reinforcing member and the improvement ofits bearing capacity

e load-vertical displacement curves of CFST speci-mens with steel tube thickness is 12mm (RS-A-2 and NS-A-2) and t steel tube thickness is 16mm (RS-B-2 and NS-B-2)composite members are shown in Figures 8 and 9

Steel tubeP1P2

Foundation21m times 13m times 1m

Hydraulic jacks

Load cell Displacement meter

L=

800m

m

h

Figure 4 Test setup (hmeans rock-socketed depth P1 steel tube is1mm P2 steel tube is 0mm)

Table 6 Material properties of the concrete core and steel tube

Steel tube Concrete Reinforcedbar

Steel tube(mm)

D 100mm M30 D 6mm Ec 16MPat 1mm mdash mdash fy 300KPa

Es 200GPaC S W 1 176

032 mdash mdash

Advances in Materials Science and Engineering 5

It can be obtained from the test results that the pro-portional limit of the load-vertical displacement curve ofreinforced CFST piles is slightly higher than unreinforcedones and the proportional limit of the specimen RS-A-2 andRS-B-2 is about 600 kN greater than 500 kN of test NS-A-2and NS-B-2 At the same time the ultimate deformationcapacity of reinforced CFST composite members is betterthan that of unreinforced CFST specimens It can be seenthat in the elastic stress stage the presence of the stressedsteel bars delays the generation of concrete cracks therebyincreasing the proportional limit of the test In the plasticstage the stressed steel bars play a further restraining roleon the core concrete which inhibits the formation and

expansion of the crack and improves the ductility and ul-timate deformation ability of the test

(2) Encased and Nonencased Members +e load-verticaldisplacement curves of plain concrete specimen (PL-2)and reinforced concrete specimen (RN-2) and reinforcedCFST composite members (RS-A-2 and RS-B-2) are shownin Figure 10 It can be seen from the test results that the steeltube has a great influence on the bearing capacity and de-formation capacity of the test For the plain concretespecimen (PL-2) the ultimate bearing capacity and ultimatedeformation are small and the maximum displacement is287mm showing the characteristics of brittle failure For the

(a) (b)

(c)

Figure 5 Failure modes (a) Plain concrete pile (b) Reinforced concrete pile (c) Unreinforced CFST pile

6 Advances in Materials Science and Engineering

reinforced concrete specimen (RN-2) the load-displacementcurve shows a certain ductility characteristic but the ultimatebearing capacity and ultimate deformation of the specimenare signicantly smaller than the reinforced CFST compositemember

313 Strain Development In this paper the strain law of thesteel casing and concrete core under the condition of an axialcompression load is described for the specimens with a steeltube thickness of 12mm (specimen RS-A-2) and 16mm(specimen RS-B-2) During the test the vertical strain andhoop strain on the side of the steel casing were monitoredand the development rule of the compressive strain inside

the core concrete was monitored Among them four straingauges are arranged on the side of the steel casing at the topandmiddle and top of the test specimen in the circumferentialdirection and the vertical strain and lateral strain of the steelcasing at this position are measured respectively In the dataprocessing the strain values of four measuring points in thesame plane are averaged to obtain the average strain of thesteel casing at the plane e load-strain curve and averagestress-strain curve of the test piece are given below Amongthem the average stress is obtained by dividing the axial loadon the specimen by the cross-sectional area

e developments of the longitudinal strain circum-ferential strain and compression behavior of the steel tubeare shown in Figures 11ndash16 Figures 11ndash13 are laws of strain

(a) (b)

Figure 6 Failure modes of reinforced CFST pile (a) Buckling deformation (b) Splitting of the steel casing weld

1200

1000

800

600

400

200

00 2 4 6 8 10 12

RS-A-2RS-B-2

14Vertical displacement (mm)

Load

(kN

)

Figure 7 Vertical displacement-load curves of two thickness steeltube-reinforced CFST piles

1000

800

600

400

200

00 2 4 6 8 10 12

RS-A-2NS-A-2

14Vertical displacement (mm)

Load

(kN

)

Figure 8 Comparison of reinforced and unreinforced CFST pileswith thickness is 12mm

Advances in Materials Science and Engineering 7

development of specimen RS-A-2 and Figures 14ndash16 arelaws of strain development of specimen RS-B-2

From the above test results it can be seen that for thesteel casing-reinforced concrete composite member thestrain value in the middle of the specimen is slightly largerthan the top and bottom strain values e strain devel-opment of steel casings at each measuring point showselastic-plastic characteristics with the increase of load Be-fore the axial load value is less than 045 times the ultimateload of the model pile foundation the load and strain showa linear relationship while the load reaches 045 times theultimate load carrying capacity After the capacity under thesame load increment the strain increment gradually in-creases showing a nonlinear characteristic From the wholeload-strain curves of the reinforced CFST specimens itexhibited the characteristics of ductile failure

In summary the use of a steel tube plays a very im-portant role in improving the compressive deformation andmechanical properties of the components For a joint steeltube-reinforced concrete structure the bearing capacity andthe ductility of the components are greatly improvedcompared to the specimens with no steel which is due to theexistence of the internal structure of the composite structureeectively enhancing the constraints between the concreteparticles to limit the development of microcracks and theeective stress

32 Columnswith Foundation It can be seen from Figure 17that the variation in the results of the dierent model col-umns under the load at the pile top is consistent and it canbe considered that the inuence of a rockless cylinder on the

1200

1000

800

600

400

200

00 2 4 6 8 10 12

RS-B-2NS-B-2

14Vertical displacement (mm)

Load

(kN

)

Figure 9 Comparison of reinforced and unreinforced CFST piles with thickness is 16mm

1000

800

600

400

200

00 2 4 6 8 10 12

RS-A-2PL-2RN-2

14Vertical displacement (mm)

Load

(kN

)

(a)

1200

1000

800

600

400

200

00 2 4 6 8 10 12 14

Vertical displacement (mm)

Load

(kN

)

RS-B-2PL-2RN-2

(b)

Figure 10 Comparison of plain concrete reinforced concrete and reinforced CFST piles

8 Advances in Materials Science and Engineering

settlement of a rock-socketed column is also consistent Itcan be seen from Figure 17 that the displacements of Z1P1and Z1P2 are basically the same from the load values of zeroto 9 kN the load-vertical displacement curve is approxi-mately a straight line and the two piles are in the elasticstage After the load exceeds 9 kN the displacement rate ofthe Z1P1 pile exceeds that of the Z1P2 pile and the settle-ment of the pile top increases e load-vertical displace-ment curves of the two piles change slowly and the processof steep drop is not obvious Figure 17 shows several settlingsthat may be due to the inhomogeneity of the model

foundation According to the above analysis it can be seenthat the vertical bearing capacities of CFST rock-socketedpiles are weaker than those rock-socketed piles withouta steel tube the dierence is mainly because the rock-socketed pile without a steel tube has a concrete-rock in-terface with a coecurrencient of friction greater than that of theCFST rock-socketed pile with a steel-rock interface

As seen from Figure 18 the greater the rock-socketeddepth the greater the load-bearing capacity of the rock-socketed piles In addition when the depth of the pile in therock-socketed increased from 3D to 5D the vertical ultimate

1000

800

600

400

200

00 2000 4000 6000

Strain (με)8000 10000 12000

Top verticalBottom verticalCentral vertical

Load

(kN

)

(a)

50

40

30

20

Ave

rage

stre

ss (M

Pa)

10

0

Strain (με)2000

Top verticalBottom verticalCentral vertical

4000 6000 8000 10000 120000

(b)

Figure 11 Vertical strain development laws of specimen RS-A-2 with steel casing (a) Relationship of vertical strain development with load(b) Relationship of vertical strain development with average stress

1000

800

600

400

200

0 1000 2000 3000Strain (με)

4000 5000 6000 7000 8000

Load

(kN

)

Top loopBottom loopCentral loop

0

(a)

50

40

30

20

10

00 1000 2000 40003000

Strain (με)5000 6000 7000 8000

Ave

rage

stre

ss (M

Pa)

Top loopBottom loopCentral loop

(b)

Figure 12 Loop strain development of specimen RS-A-2 with steel casing (a) Relationship of loop strain development with load (b)Relationship of loop strain development with average stress

Advances in Materials Science and Engineering 9

bearing capacity increased by approximately 40 e mainreason for this eect is that with the increase in the rock-socketed depth the contact area will increase and althoughthe side friction coecurrencient does not change the total frictionof the pile will signicantly increase therefore the verticalbearing capacity of the pile is signicantly improved It isfound that the vertical ultimate bearing capacity of rock-socketed piles without a steel tube (steel-free cylinder) isapproximately 10 higher than that of the steel-retainingtube when the depth of rock-embedment is the same emain reason for this phenomenon is that the outer wall ofthe pile is very smooth since its roughness is much smallerthan the concrete the corresponding side friction is lower

and the ultimate bearing capacity of the pile is equal to thepile side friction and pile end resistance decreasing theultimate bearing capacity of the pile

4 Analysis of the Ultimate Load

According to EC4 [22] the axial load capacity (NplRd) ofa CFST column can be determined by summing the yieldload of both the steel section and concrete core Forconcrete-ned tubes of circular cross section account maybe taken of increase in strength of concrete caused byconnement provided that the relative slenderness λ doesnot exceed 0 5 and edlt 0 1 where e is the eccentricity of

0 200 400 800600 1000

Concrete

1200 1400 1600Strain (με)

500

600

700

400

300

200

100

0

Load

(kN

)

(a)

Concrete

0 200 400 800600 1000 1200 1400 1600Strain (με)

30

35

25

20

15

5

10

0

Ave

rage

stre

ss (M

Pa)

(b)

Figure 13 Axial compressive strain development of core concrete of specimen RS-A-2 (a) Relationship of vertical strain development withload (b) Relationship of vertical strain development with average stress

0 2000 4000 80006000Strain (με)

10000 12000 14000

Top vertical

Bottom verticalCentral vertical

1000

1200

800

600

400

200

0

Load

(kN

)

(a)

0 2000 4000 80006000Strain (με)

10000 12000 14000

Top verticalMiddle verticalBottom vertical

50

60

40

30

20

10

0

Ave

rage

stre

ss (M

Pa)

(b)

Figure 14 Vertical strain development laws of specimen RS-B-2 with steel casing (a) Relationship of loop strain development with load (b)Relationship of loop strain development with average stress

10 Advances in Materials Science and Engineering

loading given by MEdNEd and d is the external diameter ofthe column e plastic resistance to compression may thenbe calculated from the following expression in equations(2)ndash(5) e application of EC4 [22] is restricted to com-posite columns with steel yield stress and concrete cylinderstrength of less than 355 and 50MPa respectively efollowing presents the formulations of the AISC [21] EC4[22] NBR 8800 [23 24] and GB50396-2014 [25] standardcodes to determine the resistance capacity of axially loadedCFST columns And rs is the radius of gyration of the steelhollow section le is the length of the column Ec is themodulus of elasticity of the concrete and Es is the modulusof elasticity of the steel e formulations presented were

used to calculate the compressive strength of the axiallyloaded CFST columns investigated in the present study Inaddition the boundary conditions of the testing approachare upper if the pile is loading and lower if the pile is xed

In GB50396-2014 [25] θ means the hoop coecurrencient ofconcrete-lled steel tubular members θ αscffc αsc rep-resents the steel content of concrete-lled steel tubularmembers in the design of compressive strength of concrete-lled steel tube piles B and C are the inuence factors of thecross-sectional shape on the hoop eect and about circularcross section B 0176lowast f213 + 0974 Cminus0104fc144+ 0031 In AISC [21] the axial compression member isconsidered to be the overall stability of the member the

0 1000 2000 40003000Strain (με)

5000 6000 7000

Top loopCentral loopBottom loop

1000

1200

800

600

400

200

0

Load

(kN

)

(a)

0 1000 2000 40003000Strain (με)

5000 6000 7000

Top loopCentral loopBottom loop

50

60

40

30

20

10

0

Ave

rage

stre

ss (M

Pa)

(b)

Figure 15 Loop strain development of specimen RS-B-2 with steel casing (a) Relationship of strain development with load (b) Relationshipof strain development with average stress

0 200 400 800600 1000

Concrete

1200 1400 1600 1800Strain (με)

500

600

700

800

400

300

200

100

0

Load

(kN

)

(a)

0 200 400 800600 1000

Concrete

1200 1400 1600 1800Strain (με)

30

35

40

25

20

15

5

10

0

Ave

rage

stre

ss (M

Pa)

(b)

Figure 16 Axial compressive strain development of core concrete of specimen RS-B-2

Advances in Materials Science and Engineering 11

strength of the concrete is converted into the steel thenominal compressive strength fcr of the steel is obtained andthe bearing capacity of the concrete-lled steel tubularmember is calculated from fcr fys is the yield limit of steel fckmeans the compressive strength of concrete cylinder As isthe cross-sectional area of steel pipe Ac is the cross-sectionalarea of concrete and λc is the ratio of slenderness toslenderness In Eurocode 4 (EC4) [22] the relative slen-derness λ for the plane of bending being considered is givenby λ

NPLRkNcrradic

where NplRk is the characteristic valueof the plastic resistance to compression if instead ofthe design strengths the characteristic values are used andNcr is the elastic critical normal force for the relevantbuckling mode calculated with the eective exuralstiness (EI)c

However it should be stated that the maximum allowablevalue of diameter-thickness ratio (Dt) specied in AISC [21]is 031lowast Efy the ratio of diameter-thickness of circular-section concrete-lled steel tubular members specied inChinese specication [28] should be limited to the followingrange 20

235fy

radicleDtle 85

235fy

radic and Eurocode 4 (EC4)

[22] explicit limits the allowed Dt values in the Europeancontext to 90lowast 235fy e diameter-thickness ratio of thespecimens studied in this paper is very large exceeding theallowable range of the specications e paper attempts toestimate these specimens with large diameter-thickness ratioby using the above codes And the ultimate strength calcu-lation results of relevant specications are shown in Table 7Apparently it can be found that value of the ultimate load isgenerallymuch greater than the theoretical calculation results

25

25

20

20

Z1P1Z1P2

Load

(kN

) 15

15

10

10

5

50

0Vertical displacement (mm)

(a)

Z2P2Z2P1

25

30

20

Load

(kN

)

15

10

5

025 30 3520151050

Vertical displacement (mm)

(b)

Z3P2Z3P1

30

40

20

Load

(kN

)

10

025 30 352015

Vertical displacement (mm)1050

(c)

Figure 17 Relationship of vertical displacement and load of three depths of rock-socketed columns (a) Rock-socketed depth is 300mm (P1steel tube is 1mm P2 steel tube is 0mm) (b) Rock-socketed depth is 400mm (c) Rock-socketed depth is 500mm

12 Advances in Materials Science and Engineering

AISC [21] method

Em Es + 04EcAc

As

fmy fys + 085fckAc

As

fcr 0658λ2c( )fmy if λc le 15

fcr 0877λ2c

fmy if λc le 15

λc lcrcπ

fmy

Em( )

05

NplRd 085Asfcr

(1)

EC4 and NBR 8800 [23 24] methods

NplRd η2Asfy + Acfck 1 + η1tfy

Dfck( ) (2)

η1 η10η2 η20

(3)

η10 49minus 185 times λ + 17(λ)2 ge 0 (4)

η20 025(3 + 2λ)le 10 (5)

GB50396-2014 [25] method

N0 Ascfsc

fsc 1212 + Bθ + Cθ2( )fc

αsc As

Ac

θ αscf

fc

(6)

5 Conclusion

e present study is an attempt to study the behavior ofconcrete-lled steel tube columns subjected to axialcompression Based on the results of this study the fol-lowing conclusions can be drawn within the scope of thesetests

Table 7 e ultimate strength calculation results of relevant specications

Specimens Ultimate load (kN) NBR 8800 and EC4 (kN) AISC (kN) GB50396-2014 (kN)PL-2 406 412 419 429NS-A-2 830 493 479 560NS-B-2 885 566 535 603RN-2 560 430 416 465RS-A-2 895 493 479 596RS-B-2 1190 566 535 639PL-1 480 513 519 530NS-A-1 800 428 409 478RS-A-1 895 428 409 478RS-B-1 1125 452 474 498

35

40

45

30Load

(kN

)25

2030 35 40 45 50 55

n

P1P2

Figure 18 Relationship between n and load (n ratio of rock-socketed depth n hD)

Advances in Materials Science and Engineering 13

(1) +e reinforced CFST piles exhibit two differentfailure modes When the weld strength of the steelcasing is greater than the axial load limit of thecomposite member the failure mode is the bendingfailure caused by the local buckling deformationwhich is a ductile failure feature When the weldstrength of the steel casing is less than the axial loadlimit of the composite member the failure mode isthe open splitting of the steel casing weld under theexpansion stress of the concrete which is a brittlefailure feature

(2) +e bearing capacity of rock-socketed CFSTcolumnsis lower than that of rock-socketed columns withouta steel tube under the same conditions of a verticalload +e depth of the rock inlay is clearly affectingby the bearing capacity of the two rock-socketedcolumns and the greater the rock-socketed depththe greater the bearing capacity of the rock-socketedpiles In addition the overall sliding of the steel tubeand the core concrete of pile is small and the steeltube-concrete interface is basically in a bonding stateunder the vertical load

(3) A comparison of failure loads between the tests andthe design codes was presented+e results show thatthe provisions in EC4 [22] NBR 8800 [23 24] AISC[21] and GB50396-2014 [25]conservatively estimatethe ultimate capacities of the specimens and it can befound that value of the ultimate load is generallymuch greater than the theoretical calculation resultsSince the diameter-thickness ratio of the specimensstudied in this paper is very large exceeding theallowable range of the specifications the test resultsprovide a reference for design and performance ofthe new structure with large diameter-thicknessratio

Data Availability

+e figures and tables data used to support the findings ofthis study are included within the article

Conflicts of Interest

+e authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

+is study was financially supported by the National NaturalScience Foundation of China (nos 2011550031 and51709026) and the Western Project of China (nos2011660041 and 2011560076)

References

[1] S Jegadesh and S Jayalekshmi ldquoLoad-bearing capacity ofaxially loaded circular concrete-filled steel tubular columnsrdquoProceedings of the Institution of Civil Engineers Structures andBuildings vol 169 no 7 pp 508ndash523 2016

[2] N E Shanmugam and B Lakshmi ldquoState of the art report onsteelndashconcrete composite columnsrdquo Journal of ConstructionalResearch vol 57 no 10 pp 1041ndash1080 2001

[3] S De Nardin ldquoeoretical-experimental study high strengthconcrete-filled steel tubesrdquo MS thesis EESC-USP Sao Carlos-SP 1999 in Portuguese

[4] K Cederwall B Engstrom and M Grauers ldquoHigh-strengthconcrete used in composite columnsrdquo in Proceedings of High-Strength Concretendash2nd International Symposium pp 195ndash214Detroit MI USA 1990

[5] L Han W Li and R Bjorhovde ldquoDevelopments and ad-vanced applications of concrete-filled steel tubular (CFST)structures membersrdquo Journal of Constructional Steel Re-search vol 100 pp 211ndash228 2014

[6] L Han H Shan-Hu and F Liao ldquoPerformance and calcu-lations of concrete filled steel tubes (CFST) under axialtensionrdquo Journal of Constructional Steel Research vol 67no 11 pp 1699ndash1709 2011

[7] M A Bradford ldquoDesign strength of slender concrete filledrectangular steel tubesrdquo ACI Structural Journal vol 93 no 2pp 229ndash235 1996

[8] M D OrsquoShea and R Q Bridge ldquoDesign of thin-walledconcrete filled steel tubesrdquo Journal of Structural Engineer-ing vol 126 no 11 pp 1295ndash1303 2000

[9] B Uy ldquoLocal and postlocal buckling of fabricated steel andcomposite cross sectionsrdquo Journal of Structural Engineeringvol 127 no 6 pp 666ndash677 2001

[10] K K Choi and Y Xiao ldquoAnalytical studies of concrete-filledcircular steel tubes under axial compressionrdquo Journal ofStructural Engineering vol 136 no 5 pp 565ndash573 2010

[11] Z Ou B Chen K H Hsieh M W Halling and P J BarrldquoExperimental and analytical investigation of concrete filledsteel tubular columnsrdquo Journal of Structural Engineeringvol 137 no 6 pp 635ndash645 2011

[12] T Perea R T Leon J F Hajjar and M D Denavit ldquoFull-scale tests of slender concrete-filled tubes axial behaviorrdquoJournal of Structural Engineering vol 139 no 7 pp 1249ndash1262 2013

[13] L H Han ldquoFlexural behavior of concrete-filled steel tubesrdquoJournal of Constructional Steel Research vol 60 no 2pp 313ndash337 2004

[14] L H Han ldquoFurther study on the flexural behavior ofconcrete-filled steel tubesrdquo Journal of Constructional SteelResearch vol 62 no 6 pp 554ndash565 2006

[15] H Lu L H Han and X L Zhao ldquoAnalytical behavior ofcircular concrete-filled thin-walled steel tubes subjected tobendingrdquoin-Walled Structures vol 47 no 3 pp 346ndash3582009

[16] C W Roeder D E Lehman and E Bishop ldquoStrength andstiffness of circular concrete-filled tubesrdquo Journal of StructuralEngineering vol 136 no 12 pp 1545ndash1553 2010

[17] J Moon C W Roeder D E Lehman and H Lee ldquoAnalyticalmodeling of bending of circular concrete-filled steel tubesrdquoEngineering Structures vol 42 pp 349ndash361 2012

[18] L H Han G H Yao and Z Tao ldquoPerformance of concrete-filled thin-walled steel tubes under pure torsionrdquoin-WalledStructures vol 45 no 1 pp 24ndash36 2007

[19] J Nie Y Wang and J Fan ldquoExperimental study on seismicbehavior of concrete filled steel tube columns under puretorsion and compressionndashtorsion cyclic loadrdquo Journal ofConstructional Steel Research vol 79 no 12 pp 115ndash1262013

[20] Y Wang J Nie and J Fan ldquo+eoretical model and in-vestigation of concrete filled steel tube columns under axial

14 Advances in Materials Science and Engineering

forcendashtorsion combined actionrdquo in-Walled Structuresvol 69 no 1 pp 1ndash9 2013

[21] American Institute of Steel Construction AISCndashLRFD MetricLoad and Resistance Factor Design Specification for StructuralSteel Buildings AISC Chicago IL USA 1994

[22] Europe en Comite de Normalisation ENV 1994ndash1ndash1 Euro-code 4mdashDesign of Composite Steel and Concrete StructuresPart 11 General Rules and Rules for Buildings CEN BrusselsBelgium 1994

[23] Brazilian Society of Standard Codes NBR 8800 Design andConstructional Details of Steel Structures of Buildings Bra-zilian Society of Standard Codes Rio de Janeiro Brazil 1986

[24] Brazilian Society of Standard Codes NBR 8800 BrazilianStandard Code Review Design and Constructional Details ofSteel and Composite Structures of Buildings BSSC BeloHorizonte Brazil 2003

[25] National Standards of the Peoplersquos Republic of China GB50936 Technical Code for Concrete Filled Steel TubularStructures National Standards of the Peoplersquos Republic ofChina Beijing China 2014 in Chinese

[26] Q Liu D Wang R Huang et al ldquoStudy on failure mode ofinland river large water level dock under ship impactrdquo PortEngineering Technology vol 47 no 4 2010 in Chinese

[27] J Xu ldquoStructural design of overhead vertical wharf for inlandriver large water levelrdquo Water Transport Engineeringvol 2006 pp 62ndash67 2006 in Chinese

[28] China Association for Engineering Construction Standardi-zation CECS 2890 Specification for Design and Constructionof Concrete-Filled Steel Tubular Structures China Associationfor Engineering Construction Standardization BeijingChina 2012 in Chinese

Advances in Materials Science and Engineering 15

CorrosionInternational Journal of

Hindawiwwwhindawicom Volume 2018

Advances in

Materials Science and EngineeringHindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Journal of

Chemistry

Analytical ChemistryInternational Journal of

Hindawiwwwhindawicom Volume 2018

ScienticaHindawiwwwhindawicom Volume 2018

Polymer ScienceInternational Journal of

Hindawiwwwhindawicom Volume 2018

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Advances in Condensed Matter Physics

Hindawiwwwhindawicom Volume 2018

International Journal of

BiomaterialsHindawiwwwhindawicom

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Hindawiwwwhindawicom Volume 2018

NanotechnologyHindawiwwwhindawicom Volume 2018

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Hindawiwwwhindawicom Volume 2018

High Energy PhysicsAdvances in

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom

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Volume 2018

TribologyAdvances in

Hindawiwwwhindawicom Volume 2018

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ChemistryAdvances in

Hindawiwwwhindawicom Volume 2018

Advances inPhysical Chemistry

Hindawiwwwhindawicom Volume 2018

BioMed Research InternationalMaterials

Journal of

Hindawiwwwhindawicom Volume 2018

Na

nom

ate

ria

ls

Hindawiwwwhindawicom Volume 2018

Journal ofNanomaterials

Submit your manuscripts atwwwhindawicom

jack is xed to the reaction beam and the device diagram isshown in Figure 4 During step-by-step loading to keep eachload the same the load is calculated according to 10 of theestimated carrying capacitye rst stage load is 2 times thegrading load the unloading is reduced by a consistent 20 ofthe carrying capacity e requirements are that thetransmission load is uniform continuous and stable andthat the time of loading is at least 1 minute

3 Test Results and Discussion

31 Columns without Foundation

311 Failure Modes e typical failure modes of thespecimens in this test are as followse failure modes of theplain concrete specimen (PL-2) and the reinforced concretespecimen (RN-2) are shown in Figures 5(a) and 5(b) emain failure mode is the fracture of the top concrete and thecrushing range is about one quarter of the length of the pile

e typical failure mode of the unreinforced CFSTspecimens (NS-A-2 and NS-B-2) is shown in Figure 5(c)which is mainly represented by the local buckling of thespecimen after concrete crushing

e reinforced CFST piles exhibit two dierent failuremodes e specimens with the thickness of 16mm of steelcasing (RS-B-1 and RS-B-2) locally exhibit buckling de-formation during loading the local deformation is graduallyincreased with the loading and the specimen is bent anddeformed until the bearing capacity is nally lost as shownin Figure 6(a) e specimens with the thickness of 12mm(RS-A-1 and RS-A-2) showed the same deformation char-acteristics as the specimen RS-B-1 in the early stage ofloading but when the load reaches 850 kN the weld of thesteel casing suddenly opened e specimen is destroyedinstantaneously as shown in Figure 6(b) In summary twodierent types of damage may occur in reinforced CFSTwhen axially compressed

(1) When the weld strength of the steel casing is greaterthan the axial load limit of the composite memberthe failure mode is the bending failure caused by thelocal buckling deformation which is a ductile failurefeature

(2) When the weld strength of the steel casing is less thanthe axial load limit of the composite member thefailure mode is the open splitting of the steel casingweld under the expansion stress of the concretewhich is a brittle failure feature

312 Load-Displacement Curve

(1) Reinforced and Unreinforced CFST Members e load-vertical displacement curves of reinforced CFST specimenswith steel casing thickness of 12mm (RS-A-2) and 16mm(RS-B-2) are shown in Figure 7 It can be seen from the testresults that when the thickness of the steel casing increases to16mm the displacement of the top of the specimen with theload is the same as that of the thickness of 12mm and bothexhibit obvious plastic failure properties the proportionallimit of two thicknesses is relatively close which is ap-proximately 600 kN Before the load reaches 600 kN theload-displacement curves of the two test pieces are basicallycoincident When the load exceeds 600 kN that is afterentering the plastic zone the absolute value of the dis-placement increment under the same load increment issmaller than the case where the thickness of the steel casingis 12mm under the same condition It indicates that therestraining eect of the steel casing on the core concrete ismainly reected in the plastic zone of the component whilethe eect on the elastic zone is small e maximum dis-placement that can be achieved with a thickness of 16mm is138mm which is greatly improved compared to thethickness of the steel casing of 12mm erefore thethickness of the steel casing has a great inuence on theductility of the reinforcing member and the improvement ofits bearing capacity

e load-vertical displacement curves of CFST speci-mens with steel tube thickness is 12mm (RS-A-2 and NS-A-2) and t steel tube thickness is 16mm (RS-B-2 and NS-B-2)composite members are shown in Figures 8 and 9

Steel tubeP1P2

Foundation21m times 13m times 1m

Hydraulic jacks

Load cell Displacement meter

L=

800m

m

h

Figure 4 Test setup (hmeans rock-socketed depth P1 steel tube is1mm P2 steel tube is 0mm)

Table 6 Material properties of the concrete core and steel tube

Steel tube Concrete Reinforcedbar

Steel tube(mm)

D 100mm M30 D 6mm Ec 16MPat 1mm mdash mdash fy 300KPa

Es 200GPaC S W 1 176

032 mdash mdash

Advances in Materials Science and Engineering 5

It can be obtained from the test results that the pro-portional limit of the load-vertical displacement curve ofreinforced CFST piles is slightly higher than unreinforcedones and the proportional limit of the specimen RS-A-2 andRS-B-2 is about 600 kN greater than 500 kN of test NS-A-2and NS-B-2 At the same time the ultimate deformationcapacity of reinforced CFST composite members is betterthan that of unreinforced CFST specimens It can be seenthat in the elastic stress stage the presence of the stressedsteel bars delays the generation of concrete cracks therebyincreasing the proportional limit of the test In the plasticstage the stressed steel bars play a further restraining roleon the core concrete which inhibits the formation and

expansion of the crack and improves the ductility and ul-timate deformation ability of the test

(2) Encased and Nonencased Members +e load-verticaldisplacement curves of plain concrete specimen (PL-2)and reinforced concrete specimen (RN-2) and reinforcedCFST composite members (RS-A-2 and RS-B-2) are shownin Figure 10 It can be seen from the test results that the steeltube has a great influence on the bearing capacity and de-formation capacity of the test For the plain concretespecimen (PL-2) the ultimate bearing capacity and ultimatedeformation are small and the maximum displacement is287mm showing the characteristics of brittle failure For the

(a) (b)

(c)

Figure 5 Failure modes (a) Plain concrete pile (b) Reinforced concrete pile (c) Unreinforced CFST pile

6 Advances in Materials Science and Engineering

reinforced concrete specimen (RN-2) the load-displacementcurve shows a certain ductility characteristic but the ultimatebearing capacity and ultimate deformation of the specimenare signicantly smaller than the reinforced CFST compositemember

313 Strain Development In this paper the strain law of thesteel casing and concrete core under the condition of an axialcompression load is described for the specimens with a steeltube thickness of 12mm (specimen RS-A-2) and 16mm(specimen RS-B-2) During the test the vertical strain andhoop strain on the side of the steel casing were monitoredand the development rule of the compressive strain inside

the core concrete was monitored Among them four straingauges are arranged on the side of the steel casing at the topandmiddle and top of the test specimen in the circumferentialdirection and the vertical strain and lateral strain of the steelcasing at this position are measured respectively In the dataprocessing the strain values of four measuring points in thesame plane are averaged to obtain the average strain of thesteel casing at the plane e load-strain curve and averagestress-strain curve of the test piece are given below Amongthem the average stress is obtained by dividing the axial loadon the specimen by the cross-sectional area

e developments of the longitudinal strain circum-ferential strain and compression behavior of the steel tubeare shown in Figures 11ndash16 Figures 11ndash13 are laws of strain

(a) (b)

Figure 6 Failure modes of reinforced CFST pile (a) Buckling deformation (b) Splitting of the steel casing weld

1200

1000

800

600

400

200

00 2 4 6 8 10 12

RS-A-2RS-B-2

14Vertical displacement (mm)

Load

(kN

)

Figure 7 Vertical displacement-load curves of two thickness steeltube-reinforced CFST piles

1000

800

600

400

200

00 2 4 6 8 10 12

RS-A-2NS-A-2

14Vertical displacement (mm)

Load

(kN

)

Figure 8 Comparison of reinforced and unreinforced CFST pileswith thickness is 12mm

Advances in Materials Science and Engineering 7

development of specimen RS-A-2 and Figures 14ndash16 arelaws of strain development of specimen RS-B-2

From the above test results it can be seen that for thesteel casing-reinforced concrete composite member thestrain value in the middle of the specimen is slightly largerthan the top and bottom strain values e strain devel-opment of steel casings at each measuring point showselastic-plastic characteristics with the increase of load Be-fore the axial load value is less than 045 times the ultimateload of the model pile foundation the load and strain showa linear relationship while the load reaches 045 times theultimate load carrying capacity After the capacity under thesame load increment the strain increment gradually in-creases showing a nonlinear characteristic From the wholeload-strain curves of the reinforced CFST specimens itexhibited the characteristics of ductile failure

In summary the use of a steel tube plays a very im-portant role in improving the compressive deformation andmechanical properties of the components For a joint steeltube-reinforced concrete structure the bearing capacity andthe ductility of the components are greatly improvedcompared to the specimens with no steel which is due to theexistence of the internal structure of the composite structureeectively enhancing the constraints between the concreteparticles to limit the development of microcracks and theeective stress

32 Columnswith Foundation It can be seen from Figure 17that the variation in the results of the dierent model col-umns under the load at the pile top is consistent and it canbe considered that the inuence of a rockless cylinder on the

1200

1000

800

600

400

200

00 2 4 6 8 10 12

RS-B-2NS-B-2

14Vertical displacement (mm)

Load

(kN

)

Figure 9 Comparison of reinforced and unreinforced CFST piles with thickness is 16mm

1000

800

600

400

200

00 2 4 6 8 10 12

RS-A-2PL-2RN-2

14Vertical displacement (mm)

Load

(kN

)

(a)

1200

1000

800

600

400

200

00 2 4 6 8 10 12 14

Vertical displacement (mm)

Load

(kN

)

RS-B-2PL-2RN-2

(b)

Figure 10 Comparison of plain concrete reinforced concrete and reinforced CFST piles

8 Advances in Materials Science and Engineering

settlement of a rock-socketed column is also consistent Itcan be seen from Figure 17 that the displacements of Z1P1and Z1P2 are basically the same from the load values of zeroto 9 kN the load-vertical displacement curve is approxi-mately a straight line and the two piles are in the elasticstage After the load exceeds 9 kN the displacement rate ofthe Z1P1 pile exceeds that of the Z1P2 pile and the settle-ment of the pile top increases e load-vertical displace-ment curves of the two piles change slowly and the processof steep drop is not obvious Figure 17 shows several settlingsthat may be due to the inhomogeneity of the model

foundation According to the above analysis it can be seenthat the vertical bearing capacities of CFST rock-socketedpiles are weaker than those rock-socketed piles withouta steel tube the dierence is mainly because the rock-socketed pile without a steel tube has a concrete-rock in-terface with a coecurrencient of friction greater than that of theCFST rock-socketed pile with a steel-rock interface

As seen from Figure 18 the greater the rock-socketeddepth the greater the load-bearing capacity of the rock-socketed piles In addition when the depth of the pile in therock-socketed increased from 3D to 5D the vertical ultimate

1000

800

600

400

200

00 2000 4000 6000

Strain (με)8000 10000 12000

Top verticalBottom verticalCentral vertical

Load

(kN

)

(a)

50

40

30

20

Ave

rage

stre

ss (M

Pa)

10

0

Strain (με)2000

Top verticalBottom verticalCentral vertical

4000 6000 8000 10000 120000

(b)

Figure 11 Vertical strain development laws of specimen RS-A-2 with steel casing (a) Relationship of vertical strain development with load(b) Relationship of vertical strain development with average stress

1000

800

600

400

200

0 1000 2000 3000Strain (με)

4000 5000 6000 7000 8000

Load

(kN

)

Top loopBottom loopCentral loop

0

(a)

50

40

30

20

10

00 1000 2000 40003000

Strain (με)5000 6000 7000 8000

Ave

rage

stre

ss (M

Pa)

Top loopBottom loopCentral loop

(b)

Figure 12 Loop strain development of specimen RS-A-2 with steel casing (a) Relationship of loop strain development with load (b)Relationship of loop strain development with average stress

Advances in Materials Science and Engineering 9

bearing capacity increased by approximately 40 e mainreason for this eect is that with the increase in the rock-socketed depth the contact area will increase and althoughthe side friction coecurrencient does not change the total frictionof the pile will signicantly increase therefore the verticalbearing capacity of the pile is signicantly improved It isfound that the vertical ultimate bearing capacity of rock-socketed piles without a steel tube (steel-free cylinder) isapproximately 10 higher than that of the steel-retainingtube when the depth of rock-embedment is the same emain reason for this phenomenon is that the outer wall ofthe pile is very smooth since its roughness is much smallerthan the concrete the corresponding side friction is lower

and the ultimate bearing capacity of the pile is equal to thepile side friction and pile end resistance decreasing theultimate bearing capacity of the pile

4 Analysis of the Ultimate Load

According to EC4 [22] the axial load capacity (NplRd) ofa CFST column can be determined by summing the yieldload of both the steel section and concrete core Forconcrete-ned tubes of circular cross section account maybe taken of increase in strength of concrete caused byconnement provided that the relative slenderness λ doesnot exceed 0 5 and edlt 0 1 where e is the eccentricity of

0 200 400 800600 1000

Concrete

1200 1400 1600Strain (με)

500

600

700

400

300

200

100

0

Load

(kN

)

(a)

Concrete

0 200 400 800600 1000 1200 1400 1600Strain (με)

30

35

25

20

15

5

10

0

Ave

rage

stre

ss (M

Pa)

(b)

Figure 13 Axial compressive strain development of core concrete of specimen RS-A-2 (a) Relationship of vertical strain development withload (b) Relationship of vertical strain development with average stress

0 2000 4000 80006000Strain (με)

10000 12000 14000

Top vertical

Bottom verticalCentral vertical

1000

1200

800

600

400

200

0

Load

(kN

)

(a)

0 2000 4000 80006000Strain (με)

10000 12000 14000

Top verticalMiddle verticalBottom vertical

50

60

40

30

20

10

0

Ave

rage

stre

ss (M

Pa)

(b)

Figure 14 Vertical strain development laws of specimen RS-B-2 with steel casing (a) Relationship of loop strain development with load (b)Relationship of loop strain development with average stress

10 Advances in Materials Science and Engineering

loading given by MEdNEd and d is the external diameter ofthe column e plastic resistance to compression may thenbe calculated from the following expression in equations(2)ndash(5) e application of EC4 [22] is restricted to com-posite columns with steel yield stress and concrete cylinderstrength of less than 355 and 50MPa respectively efollowing presents the formulations of the AISC [21] EC4[22] NBR 8800 [23 24] and GB50396-2014 [25] standardcodes to determine the resistance capacity of axially loadedCFST columns And rs is the radius of gyration of the steelhollow section le is the length of the column Ec is themodulus of elasticity of the concrete and Es is the modulusof elasticity of the steel e formulations presented were

used to calculate the compressive strength of the axiallyloaded CFST columns investigated in the present study Inaddition the boundary conditions of the testing approachare upper if the pile is loading and lower if the pile is xed

In GB50396-2014 [25] θ means the hoop coecurrencient ofconcrete-lled steel tubular members θ αscffc αsc rep-resents the steel content of concrete-lled steel tubularmembers in the design of compressive strength of concrete-lled steel tube piles B and C are the inuence factors of thecross-sectional shape on the hoop eect and about circularcross section B 0176lowast f213 + 0974 Cminus0104fc144+ 0031 In AISC [21] the axial compression member isconsidered to be the overall stability of the member the

0 1000 2000 40003000Strain (με)

5000 6000 7000

Top loopCentral loopBottom loop

1000

1200

800

600

400

200

0

Load

(kN

)

(a)

0 1000 2000 40003000Strain (με)

5000 6000 7000

Top loopCentral loopBottom loop

50

60

40

30

20

10

0

Ave

rage

stre

ss (M

Pa)

(b)

Figure 15 Loop strain development of specimen RS-B-2 with steel casing (a) Relationship of strain development with load (b) Relationshipof strain development with average stress

0 200 400 800600 1000

Concrete

1200 1400 1600 1800Strain (με)

500

600

700

800

400

300

200

100

0

Load

(kN

)

(a)

0 200 400 800600 1000

Concrete

1200 1400 1600 1800Strain (με)

30

35

40

25

20

15

5

10

0

Ave

rage

stre

ss (M

Pa)

(b)

Figure 16 Axial compressive strain development of core concrete of specimen RS-B-2

Advances in Materials Science and Engineering 11

strength of the concrete is converted into the steel thenominal compressive strength fcr of the steel is obtained andthe bearing capacity of the concrete-lled steel tubularmember is calculated from fcr fys is the yield limit of steel fckmeans the compressive strength of concrete cylinder As isthe cross-sectional area of steel pipe Ac is the cross-sectionalarea of concrete and λc is the ratio of slenderness toslenderness In Eurocode 4 (EC4) [22] the relative slen-derness λ for the plane of bending being considered is givenby λ

NPLRkNcrradic

where NplRk is the characteristic valueof the plastic resistance to compression if instead ofthe design strengths the characteristic values are used andNcr is the elastic critical normal force for the relevantbuckling mode calculated with the eective exuralstiness (EI)c

However it should be stated that the maximum allowablevalue of diameter-thickness ratio (Dt) specied in AISC [21]is 031lowast Efy the ratio of diameter-thickness of circular-section concrete-lled steel tubular members specied inChinese specication [28] should be limited to the followingrange 20

235fy

radicleDtle 85

235fy

radic and Eurocode 4 (EC4)

[22] explicit limits the allowed Dt values in the Europeancontext to 90lowast 235fy e diameter-thickness ratio of thespecimens studied in this paper is very large exceeding theallowable range of the specications e paper attempts toestimate these specimens with large diameter-thickness ratioby using the above codes And the ultimate strength calcu-lation results of relevant specications are shown in Table 7Apparently it can be found that value of the ultimate load isgenerallymuch greater than the theoretical calculation results

25

25

20

20

Z1P1Z1P2

Load

(kN

) 15

15

10

10

5

50

0Vertical displacement (mm)

(a)

Z2P2Z2P1

25

30

20

Load

(kN

)

15

10

5

025 30 3520151050

Vertical displacement (mm)

(b)

Z3P2Z3P1

30

40

20

Load

(kN

)

10

025 30 352015

Vertical displacement (mm)1050

(c)

Figure 17 Relationship of vertical displacement and load of three depths of rock-socketed columns (a) Rock-socketed depth is 300mm (P1steel tube is 1mm P2 steel tube is 0mm) (b) Rock-socketed depth is 400mm (c) Rock-socketed depth is 500mm

12 Advances in Materials Science and Engineering

AISC [21] method

Em Es + 04EcAc

As

fmy fys + 085fckAc

As

fcr 0658λ2c( )fmy if λc le 15

fcr 0877λ2c

fmy if λc le 15

λc lcrcπ

fmy

Em( )

05

NplRd 085Asfcr

(1)

EC4 and NBR 8800 [23 24] methods

NplRd η2Asfy + Acfck 1 + η1tfy

Dfck( ) (2)

η1 η10η2 η20

(3)

η10 49minus 185 times λ + 17(λ)2 ge 0 (4)

η20 025(3 + 2λ)le 10 (5)

GB50396-2014 [25] method

N0 Ascfsc

fsc 1212 + Bθ + Cθ2( )fc

αsc As

Ac

θ αscf

fc

(6)

5 Conclusion

e present study is an attempt to study the behavior ofconcrete-lled steel tube columns subjected to axialcompression Based on the results of this study the fol-lowing conclusions can be drawn within the scope of thesetests

Table 7 e ultimate strength calculation results of relevant specications

Specimens Ultimate load (kN) NBR 8800 and EC4 (kN) AISC (kN) GB50396-2014 (kN)PL-2 406 412 419 429NS-A-2 830 493 479 560NS-B-2 885 566 535 603RN-2 560 430 416 465RS-A-2 895 493 479 596RS-B-2 1190 566 535 639PL-1 480 513 519 530NS-A-1 800 428 409 478RS-A-1 895 428 409 478RS-B-1 1125 452 474 498

35

40

45

30Load

(kN

)25

2030 35 40 45 50 55

n

P1P2

Figure 18 Relationship between n and load (n ratio of rock-socketed depth n hD)

Advances in Materials Science and Engineering 13

(1) +e reinforced CFST piles exhibit two differentfailure modes When the weld strength of the steelcasing is greater than the axial load limit of thecomposite member the failure mode is the bendingfailure caused by the local buckling deformationwhich is a ductile failure feature When the weldstrength of the steel casing is less than the axial loadlimit of the composite member the failure mode isthe open splitting of the steel casing weld under theexpansion stress of the concrete which is a brittlefailure feature

(2) +e bearing capacity of rock-socketed CFSTcolumnsis lower than that of rock-socketed columns withouta steel tube under the same conditions of a verticalload +e depth of the rock inlay is clearly affectingby the bearing capacity of the two rock-socketedcolumns and the greater the rock-socketed depththe greater the bearing capacity of the rock-socketedpiles In addition the overall sliding of the steel tubeand the core concrete of pile is small and the steeltube-concrete interface is basically in a bonding stateunder the vertical load

(3) A comparison of failure loads between the tests andthe design codes was presented+e results show thatthe provisions in EC4 [22] NBR 8800 [23 24] AISC[21] and GB50396-2014 [25]conservatively estimatethe ultimate capacities of the specimens and it can befound that value of the ultimate load is generallymuch greater than the theoretical calculation resultsSince the diameter-thickness ratio of the specimensstudied in this paper is very large exceeding theallowable range of the specifications the test resultsprovide a reference for design and performance ofthe new structure with large diameter-thicknessratio

Data Availability

+e figures and tables data used to support the findings ofthis study are included within the article

Conflicts of Interest

+e authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

+is study was financially supported by the National NaturalScience Foundation of China (nos 2011550031 and51709026) and the Western Project of China (nos2011660041 and 2011560076)

References

[1] S Jegadesh and S Jayalekshmi ldquoLoad-bearing capacity ofaxially loaded circular concrete-filled steel tubular columnsrdquoProceedings of the Institution of Civil Engineers Structures andBuildings vol 169 no 7 pp 508ndash523 2016

[2] N E Shanmugam and B Lakshmi ldquoState of the art report onsteelndashconcrete composite columnsrdquo Journal of ConstructionalResearch vol 57 no 10 pp 1041ndash1080 2001

[3] S De Nardin ldquoeoretical-experimental study high strengthconcrete-filled steel tubesrdquo MS thesis EESC-USP Sao Carlos-SP 1999 in Portuguese

[4] K Cederwall B Engstrom and M Grauers ldquoHigh-strengthconcrete used in composite columnsrdquo in Proceedings of High-Strength Concretendash2nd International Symposium pp 195ndash214Detroit MI USA 1990

[5] L Han W Li and R Bjorhovde ldquoDevelopments and ad-vanced applications of concrete-filled steel tubular (CFST)structures membersrdquo Journal of Constructional Steel Re-search vol 100 pp 211ndash228 2014

[6] L Han H Shan-Hu and F Liao ldquoPerformance and calcu-lations of concrete filled steel tubes (CFST) under axialtensionrdquo Journal of Constructional Steel Research vol 67no 11 pp 1699ndash1709 2011

[7] M A Bradford ldquoDesign strength of slender concrete filledrectangular steel tubesrdquo ACI Structural Journal vol 93 no 2pp 229ndash235 1996

[8] M D OrsquoShea and R Q Bridge ldquoDesign of thin-walledconcrete filled steel tubesrdquo Journal of Structural Engineer-ing vol 126 no 11 pp 1295ndash1303 2000

[9] B Uy ldquoLocal and postlocal buckling of fabricated steel andcomposite cross sectionsrdquo Journal of Structural Engineeringvol 127 no 6 pp 666ndash677 2001

[10] K K Choi and Y Xiao ldquoAnalytical studies of concrete-filledcircular steel tubes under axial compressionrdquo Journal ofStructural Engineering vol 136 no 5 pp 565ndash573 2010

[11] Z Ou B Chen K H Hsieh M W Halling and P J BarrldquoExperimental and analytical investigation of concrete filledsteel tubular columnsrdquo Journal of Structural Engineeringvol 137 no 6 pp 635ndash645 2011

[12] T Perea R T Leon J F Hajjar and M D Denavit ldquoFull-scale tests of slender concrete-filled tubes axial behaviorrdquoJournal of Structural Engineering vol 139 no 7 pp 1249ndash1262 2013

[13] L H Han ldquoFlexural behavior of concrete-filled steel tubesrdquoJournal of Constructional Steel Research vol 60 no 2pp 313ndash337 2004

[14] L H Han ldquoFurther study on the flexural behavior ofconcrete-filled steel tubesrdquo Journal of Constructional SteelResearch vol 62 no 6 pp 554ndash565 2006

[15] H Lu L H Han and X L Zhao ldquoAnalytical behavior ofcircular concrete-filled thin-walled steel tubes subjected tobendingrdquoin-Walled Structures vol 47 no 3 pp 346ndash3582009

[16] C W Roeder D E Lehman and E Bishop ldquoStrength andstiffness of circular concrete-filled tubesrdquo Journal of StructuralEngineering vol 136 no 12 pp 1545ndash1553 2010

[17] J Moon C W Roeder D E Lehman and H Lee ldquoAnalyticalmodeling of bending of circular concrete-filled steel tubesrdquoEngineering Structures vol 42 pp 349ndash361 2012

[18] L H Han G H Yao and Z Tao ldquoPerformance of concrete-filled thin-walled steel tubes under pure torsionrdquoin-WalledStructures vol 45 no 1 pp 24ndash36 2007

[19] J Nie Y Wang and J Fan ldquoExperimental study on seismicbehavior of concrete filled steel tube columns under puretorsion and compressionndashtorsion cyclic loadrdquo Journal ofConstructional Steel Research vol 79 no 12 pp 115ndash1262013

[20] Y Wang J Nie and J Fan ldquo+eoretical model and in-vestigation of concrete filled steel tube columns under axial

14 Advances in Materials Science and Engineering

forcendashtorsion combined actionrdquo in-Walled Structuresvol 69 no 1 pp 1ndash9 2013

[21] American Institute of Steel Construction AISCndashLRFD MetricLoad and Resistance Factor Design Specification for StructuralSteel Buildings AISC Chicago IL USA 1994

[22] Europe en Comite de Normalisation ENV 1994ndash1ndash1 Euro-code 4mdashDesign of Composite Steel and Concrete StructuresPart 11 General Rules and Rules for Buildings CEN BrusselsBelgium 1994

[23] Brazilian Society of Standard Codes NBR 8800 Design andConstructional Details of Steel Structures of Buildings Bra-zilian Society of Standard Codes Rio de Janeiro Brazil 1986

[24] Brazilian Society of Standard Codes NBR 8800 BrazilianStandard Code Review Design and Constructional Details ofSteel and Composite Structures of Buildings BSSC BeloHorizonte Brazil 2003

[25] National Standards of the Peoplersquos Republic of China GB50936 Technical Code for Concrete Filled Steel TubularStructures National Standards of the Peoplersquos Republic ofChina Beijing China 2014 in Chinese

[26] Q Liu D Wang R Huang et al ldquoStudy on failure mode ofinland river large water level dock under ship impactrdquo PortEngineering Technology vol 47 no 4 2010 in Chinese

[27] J Xu ldquoStructural design of overhead vertical wharf for inlandriver large water levelrdquo Water Transport Engineeringvol 2006 pp 62ndash67 2006 in Chinese

[28] China Association for Engineering Construction Standardi-zation CECS 2890 Specification for Design and Constructionof Concrete-Filled Steel Tubular Structures China Associationfor Engineering Construction Standardization BeijingChina 2012 in Chinese

Advances in Materials Science and Engineering 15

CorrosionInternational Journal of

Hindawiwwwhindawicom Volume 2018

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Materials Science and EngineeringHindawiwwwhindawicom Volume 2018

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Analytical ChemistryInternational Journal of

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ChemistryAdvances in

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Hindawiwwwhindawicom Volume 2018

BioMed Research InternationalMaterials

Journal of

Hindawiwwwhindawicom Volume 2018

Na

nom

ate

ria

ls

Hindawiwwwhindawicom Volume 2018

Journal ofNanomaterials

Submit your manuscripts atwwwhindawicom

It can be obtained from the test results that the pro-portional limit of the load-vertical displacement curve ofreinforced CFST piles is slightly higher than unreinforcedones and the proportional limit of the specimen RS-A-2 andRS-B-2 is about 600 kN greater than 500 kN of test NS-A-2and NS-B-2 At the same time the ultimate deformationcapacity of reinforced CFST composite members is betterthan that of unreinforced CFST specimens It can be seenthat in the elastic stress stage the presence of the stressedsteel bars delays the generation of concrete cracks therebyincreasing the proportional limit of the test In the plasticstage the stressed steel bars play a further restraining roleon the core concrete which inhibits the formation and

expansion of the crack and improves the ductility and ul-timate deformation ability of the test

(2) Encased and Nonencased Members +e load-verticaldisplacement curves of plain concrete specimen (PL-2)and reinforced concrete specimen (RN-2) and reinforcedCFST composite members (RS-A-2 and RS-B-2) are shownin Figure 10 It can be seen from the test results that the steeltube has a great influence on the bearing capacity and de-formation capacity of the test For the plain concretespecimen (PL-2) the ultimate bearing capacity and ultimatedeformation are small and the maximum displacement is287mm showing the characteristics of brittle failure For the

(a) (b)

(c)

Figure 5 Failure modes (a) Plain concrete pile (b) Reinforced concrete pile (c) Unreinforced CFST pile

6 Advances in Materials Science and Engineering

reinforced concrete specimen (RN-2) the load-displacementcurve shows a certain ductility characteristic but the ultimatebearing capacity and ultimate deformation of the specimenare signicantly smaller than the reinforced CFST compositemember

313 Strain Development In this paper the strain law of thesteel casing and concrete core under the condition of an axialcompression load is described for the specimens with a steeltube thickness of 12mm (specimen RS-A-2) and 16mm(specimen RS-B-2) During the test the vertical strain andhoop strain on the side of the steel casing were monitoredand the development rule of the compressive strain inside

the core concrete was monitored Among them four straingauges are arranged on the side of the steel casing at the topandmiddle and top of the test specimen in the circumferentialdirection and the vertical strain and lateral strain of the steelcasing at this position are measured respectively In the dataprocessing the strain values of four measuring points in thesame plane are averaged to obtain the average strain of thesteel casing at the plane e load-strain curve and averagestress-strain curve of the test piece are given below Amongthem the average stress is obtained by dividing the axial loadon the specimen by the cross-sectional area

e developments of the longitudinal strain circum-ferential strain and compression behavior of the steel tubeare shown in Figures 11ndash16 Figures 11ndash13 are laws of strain

(a) (b)

Figure 6 Failure modes of reinforced CFST pile (a) Buckling deformation (b) Splitting of the steel casing weld

1200

1000

800

600

400

200

00 2 4 6 8 10 12

RS-A-2RS-B-2

14Vertical displacement (mm)

Load

(kN

)

Figure 7 Vertical displacement-load curves of two thickness steeltube-reinforced CFST piles

1000

800

600

400

200

00 2 4 6 8 10 12

RS-A-2NS-A-2

14Vertical displacement (mm)

Load

(kN

)

Figure 8 Comparison of reinforced and unreinforced CFST pileswith thickness is 12mm

Advances in Materials Science and Engineering 7

development of specimen RS-A-2 and Figures 14ndash16 arelaws of strain development of specimen RS-B-2

From the above test results it can be seen that for thesteel casing-reinforced concrete composite member thestrain value in the middle of the specimen is slightly largerthan the top and bottom strain values e strain devel-opment of steel casings at each measuring point showselastic-plastic characteristics with the increase of load Be-fore the axial load value is less than 045 times the ultimateload of the model pile foundation the load and strain showa linear relationship while the load reaches 045 times theultimate load carrying capacity After the capacity under thesame load increment the strain increment gradually in-creases showing a nonlinear characteristic From the wholeload-strain curves of the reinforced CFST specimens itexhibited the characteristics of ductile failure

In summary the use of a steel tube plays a very im-portant role in improving the compressive deformation andmechanical properties of the components For a joint steeltube-reinforced concrete structure the bearing capacity andthe ductility of the components are greatly improvedcompared to the specimens with no steel which is due to theexistence of the internal structure of the composite structureeectively enhancing the constraints between the concreteparticles to limit the development of microcracks and theeective stress

32 Columnswith Foundation It can be seen from Figure 17that the variation in the results of the dierent model col-umns under the load at the pile top is consistent and it canbe considered that the inuence of a rockless cylinder on the

1200

1000

800

600

400

200

00 2 4 6 8 10 12

RS-B-2NS-B-2

14Vertical displacement (mm)

Load

(kN

)

Figure 9 Comparison of reinforced and unreinforced CFST piles with thickness is 16mm

1000

800

600

400

200

00 2 4 6 8 10 12

RS-A-2PL-2RN-2

14Vertical displacement (mm)

Load

(kN

)

(a)

1200

1000

800

600

400

200

00 2 4 6 8 10 12 14

Vertical displacement (mm)

Load

(kN

)

RS-B-2PL-2RN-2

(b)

Figure 10 Comparison of plain concrete reinforced concrete and reinforced CFST piles

8 Advances in Materials Science and Engineering

settlement of a rock-socketed column is also consistent Itcan be seen from Figure 17 that the displacements of Z1P1and Z1P2 are basically the same from the load values of zeroto 9 kN the load-vertical displacement curve is approxi-mately a straight line and the two piles are in the elasticstage After the load exceeds 9 kN the displacement rate ofthe Z1P1 pile exceeds that of the Z1P2 pile and the settle-ment of the pile top increases e load-vertical displace-ment curves of the two piles change slowly and the processof steep drop is not obvious Figure 17 shows several settlingsthat may be due to the inhomogeneity of the model

foundation According to the above analysis it can be seenthat the vertical bearing capacities of CFST rock-socketedpiles are weaker than those rock-socketed piles withouta steel tube the dierence is mainly because the rock-socketed pile without a steel tube has a concrete-rock in-terface with a coecurrencient of friction greater than that of theCFST rock-socketed pile with a steel-rock interface

As seen from Figure 18 the greater the rock-socketeddepth the greater the load-bearing capacity of the rock-socketed piles In addition when the depth of the pile in therock-socketed increased from 3D to 5D the vertical ultimate

1000

800

600

400

200

00 2000 4000 6000

Strain (με)8000 10000 12000

Top verticalBottom verticalCentral vertical

Load

(kN

)

(a)

50

40

30

20

Ave

rage

stre

ss (M

Pa)

10

0

Strain (με)2000

Top verticalBottom verticalCentral vertical

4000 6000 8000 10000 120000

(b)

Figure 11 Vertical strain development laws of specimen RS-A-2 with steel casing (a) Relationship of vertical strain development with load(b) Relationship of vertical strain development with average stress

1000

800

600

400

200

0 1000 2000 3000Strain (με)

4000 5000 6000 7000 8000

Load

(kN

)

Top loopBottom loopCentral loop

0

(a)

50

40

30

20

10

00 1000 2000 40003000

Strain (με)5000 6000 7000 8000

Ave

rage

stre

ss (M

Pa)

Top loopBottom loopCentral loop

(b)

Figure 12 Loop strain development of specimen RS-A-2 with steel casing (a) Relationship of loop strain development with load (b)Relationship of loop strain development with average stress

Advances in Materials Science and Engineering 9

bearing capacity increased by approximately 40 e mainreason for this eect is that with the increase in the rock-socketed depth the contact area will increase and althoughthe side friction coecurrencient does not change the total frictionof the pile will signicantly increase therefore the verticalbearing capacity of the pile is signicantly improved It isfound that the vertical ultimate bearing capacity of rock-socketed piles without a steel tube (steel-free cylinder) isapproximately 10 higher than that of the steel-retainingtube when the depth of rock-embedment is the same emain reason for this phenomenon is that the outer wall ofthe pile is very smooth since its roughness is much smallerthan the concrete the corresponding side friction is lower

and the ultimate bearing capacity of the pile is equal to thepile side friction and pile end resistance decreasing theultimate bearing capacity of the pile

4 Analysis of the Ultimate Load

According to EC4 [22] the axial load capacity (NplRd) ofa CFST column can be determined by summing the yieldload of both the steel section and concrete core Forconcrete-ned tubes of circular cross section account maybe taken of increase in strength of concrete caused byconnement provided that the relative slenderness λ doesnot exceed 0 5 and edlt 0 1 where e is the eccentricity of

0 200 400 800600 1000

Concrete

1200 1400 1600Strain (με)

500

600

700

400

300

200

100

0

Load

(kN

)

(a)

Concrete

0 200 400 800600 1000 1200 1400 1600Strain (με)

30

35

25

20

15

5

10

0

Ave

rage

stre

ss (M

Pa)

(b)

Figure 13 Axial compressive strain development of core concrete of specimen RS-A-2 (a) Relationship of vertical strain development withload (b) Relationship of vertical strain development with average stress

0 2000 4000 80006000Strain (με)

10000 12000 14000

Top vertical

Bottom verticalCentral vertical

1000

1200

800

600

400

200

0

Load

(kN

)

(a)

0 2000 4000 80006000Strain (με)

10000 12000 14000

Top verticalMiddle verticalBottom vertical

50

60

40

30

20

10

0

Ave

rage

stre

ss (M

Pa)

(b)

Figure 14 Vertical strain development laws of specimen RS-B-2 with steel casing (a) Relationship of loop strain development with load (b)Relationship of loop strain development with average stress

10 Advances in Materials Science and Engineering

loading given by MEdNEd and d is the external diameter ofthe column e plastic resistance to compression may thenbe calculated from the following expression in equations(2)ndash(5) e application of EC4 [22] is restricted to com-posite columns with steel yield stress and concrete cylinderstrength of less than 355 and 50MPa respectively efollowing presents the formulations of the AISC [21] EC4[22] NBR 8800 [23 24] and GB50396-2014 [25] standardcodes to determine the resistance capacity of axially loadedCFST columns And rs is the radius of gyration of the steelhollow section le is the length of the column Ec is themodulus of elasticity of the concrete and Es is the modulusof elasticity of the steel e formulations presented were

used to calculate the compressive strength of the axiallyloaded CFST columns investigated in the present study Inaddition the boundary conditions of the testing approachare upper if the pile is loading and lower if the pile is xed

In GB50396-2014 [25] θ means the hoop coecurrencient ofconcrete-lled steel tubular members θ αscffc αsc rep-resents the steel content of concrete-lled steel tubularmembers in the design of compressive strength of concrete-lled steel tube piles B and C are the inuence factors of thecross-sectional shape on the hoop eect and about circularcross section B 0176lowast f213 + 0974 Cminus0104fc144+ 0031 In AISC [21] the axial compression member isconsidered to be the overall stability of the member the

0 1000 2000 40003000Strain (με)

5000 6000 7000

Top loopCentral loopBottom loop

1000

1200

800

600

400

200

0

Load

(kN

)

(a)

0 1000 2000 40003000Strain (με)

5000 6000 7000

Top loopCentral loopBottom loop

50

60

40

30

20

10

0

Ave

rage

stre

ss (M

Pa)

(b)

Figure 15 Loop strain development of specimen RS-B-2 with steel casing (a) Relationship of strain development with load (b) Relationshipof strain development with average stress

0 200 400 800600 1000

Concrete

1200 1400 1600 1800Strain (με)

500

600

700

800

400

300

200

100

0

Load

(kN

)

(a)

0 200 400 800600 1000

Concrete

1200 1400 1600 1800Strain (με)

30

35

40

25

20

15

5

10

0

Ave

rage

stre

ss (M

Pa)

(b)

Figure 16 Axial compressive strain development of core concrete of specimen RS-B-2

Advances in Materials Science and Engineering 11

strength of the concrete is converted into the steel thenominal compressive strength fcr of the steel is obtained andthe bearing capacity of the concrete-lled steel tubularmember is calculated from fcr fys is the yield limit of steel fckmeans the compressive strength of concrete cylinder As isthe cross-sectional area of steel pipe Ac is the cross-sectionalarea of concrete and λc is the ratio of slenderness toslenderness In Eurocode 4 (EC4) [22] the relative slen-derness λ for the plane of bending being considered is givenby λ

NPLRkNcrradic

where NplRk is the characteristic valueof the plastic resistance to compression if instead ofthe design strengths the characteristic values are used andNcr is the elastic critical normal force for the relevantbuckling mode calculated with the eective exuralstiness (EI)c

However it should be stated that the maximum allowablevalue of diameter-thickness ratio (Dt) specied in AISC [21]is 031lowast Efy the ratio of diameter-thickness of circular-section concrete-lled steel tubular members specied inChinese specication [28] should be limited to the followingrange 20

235fy

radicleDtle 85

235fy

radic and Eurocode 4 (EC4)

[22] explicit limits the allowed Dt values in the Europeancontext to 90lowast 235fy e diameter-thickness ratio of thespecimens studied in this paper is very large exceeding theallowable range of the specications e paper attempts toestimate these specimens with large diameter-thickness ratioby using the above codes And the ultimate strength calcu-lation results of relevant specications are shown in Table 7Apparently it can be found that value of the ultimate load isgenerallymuch greater than the theoretical calculation results

25

25

20

20

Z1P1Z1P2

Load

(kN

) 15

15

10

10

5

50

0Vertical displacement (mm)

(a)

Z2P2Z2P1

25

30

20

Load

(kN

)

15

10

5

025 30 3520151050

Vertical displacement (mm)

(b)

Z3P2Z3P1

30

40

20

Load

(kN

)

10

025 30 352015

Vertical displacement (mm)1050

(c)

Figure 17 Relationship of vertical displacement and load of three depths of rock-socketed columns (a) Rock-socketed depth is 300mm (P1steel tube is 1mm P2 steel tube is 0mm) (b) Rock-socketed depth is 400mm (c) Rock-socketed depth is 500mm

12 Advances in Materials Science and Engineering

AISC [21] method

Em Es + 04EcAc

As

fmy fys + 085fckAc

As

fcr 0658λ2c( )fmy if λc le 15

fcr 0877λ2c

fmy if λc le 15

λc lcrcπ

fmy

Em( )

05

NplRd 085Asfcr

(1)

EC4 and NBR 8800 [23 24] methods

NplRd η2Asfy + Acfck 1 + η1tfy

Dfck( ) (2)

η1 η10η2 η20

(3)

η10 49minus 185 times λ + 17(λ)2 ge 0 (4)

η20 025(3 + 2λ)le 10 (5)

GB50396-2014 [25] method

N0 Ascfsc

fsc 1212 + Bθ + Cθ2( )fc

αsc As

Ac

θ αscf

fc

(6)

5 Conclusion

e present study is an attempt to study the behavior ofconcrete-lled steel tube columns subjected to axialcompression Based on the results of this study the fol-lowing conclusions can be drawn within the scope of thesetests

Table 7 e ultimate strength calculation results of relevant specications

Specimens Ultimate load (kN) NBR 8800 and EC4 (kN) AISC (kN) GB50396-2014 (kN)PL-2 406 412 419 429NS-A-2 830 493 479 560NS-B-2 885 566 535 603RN-2 560 430 416 465RS-A-2 895 493 479 596RS-B-2 1190 566 535 639PL-1 480 513 519 530NS-A-1 800 428 409 478RS-A-1 895 428 409 478RS-B-1 1125 452 474 498

35

40

45

30Load

(kN

)25

2030 35 40 45 50 55

n

P1P2

Figure 18 Relationship between n and load (n ratio of rock-socketed depth n hD)

Advances in Materials Science and Engineering 13

(1) +e reinforced CFST piles exhibit two differentfailure modes When the weld strength of the steelcasing is greater than the axial load limit of thecomposite member the failure mode is the bendingfailure caused by the local buckling deformationwhich is a ductile failure feature When the weldstrength of the steel casing is less than the axial loadlimit of the composite member the failure mode isthe open splitting of the steel casing weld under theexpansion stress of the concrete which is a brittlefailure feature

(2) +e bearing capacity of rock-socketed CFSTcolumnsis lower than that of rock-socketed columns withouta steel tube under the same conditions of a verticalload +e depth of the rock inlay is clearly affectingby the bearing capacity of the two rock-socketedcolumns and the greater the rock-socketed depththe greater the bearing capacity of the rock-socketedpiles In addition the overall sliding of the steel tubeand the core concrete of pile is small and the steeltube-concrete interface is basically in a bonding stateunder the vertical load

(3) A comparison of failure loads between the tests andthe design codes was presented+e results show thatthe provisions in EC4 [22] NBR 8800 [23 24] AISC[21] and GB50396-2014 [25]conservatively estimatethe ultimate capacities of the specimens and it can befound that value of the ultimate load is generallymuch greater than the theoretical calculation resultsSince the diameter-thickness ratio of the specimensstudied in this paper is very large exceeding theallowable range of the specifications the test resultsprovide a reference for design and performance ofthe new structure with large diameter-thicknessratio

Data Availability

+e figures and tables data used to support the findings ofthis study are included within the article

Conflicts of Interest

+e authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

+is study was financially supported by the National NaturalScience Foundation of China (nos 2011550031 and51709026) and the Western Project of China (nos2011660041 and 2011560076)

References

[1] S Jegadesh and S Jayalekshmi ldquoLoad-bearing capacity ofaxially loaded circular concrete-filled steel tubular columnsrdquoProceedings of the Institution of Civil Engineers Structures andBuildings vol 169 no 7 pp 508ndash523 2016

[2] N E Shanmugam and B Lakshmi ldquoState of the art report onsteelndashconcrete composite columnsrdquo Journal of ConstructionalResearch vol 57 no 10 pp 1041ndash1080 2001

[3] S De Nardin ldquoeoretical-experimental study high strengthconcrete-filled steel tubesrdquo MS thesis EESC-USP Sao Carlos-SP 1999 in Portuguese

[4] K Cederwall B Engstrom and M Grauers ldquoHigh-strengthconcrete used in composite columnsrdquo in Proceedings of High-Strength Concretendash2nd International Symposium pp 195ndash214Detroit MI USA 1990

[5] L Han W Li and R Bjorhovde ldquoDevelopments and ad-vanced applications of concrete-filled steel tubular (CFST)structures membersrdquo Journal of Constructional Steel Re-search vol 100 pp 211ndash228 2014

[6] L Han H Shan-Hu and F Liao ldquoPerformance and calcu-lations of concrete filled steel tubes (CFST) under axialtensionrdquo Journal of Constructional Steel Research vol 67no 11 pp 1699ndash1709 2011

[7] M A Bradford ldquoDesign strength of slender concrete filledrectangular steel tubesrdquo ACI Structural Journal vol 93 no 2pp 229ndash235 1996

[8] M D OrsquoShea and R Q Bridge ldquoDesign of thin-walledconcrete filled steel tubesrdquo Journal of Structural Engineer-ing vol 126 no 11 pp 1295ndash1303 2000

[9] B Uy ldquoLocal and postlocal buckling of fabricated steel andcomposite cross sectionsrdquo Journal of Structural Engineeringvol 127 no 6 pp 666ndash677 2001

[10] K K Choi and Y Xiao ldquoAnalytical studies of concrete-filledcircular steel tubes under axial compressionrdquo Journal ofStructural Engineering vol 136 no 5 pp 565ndash573 2010

[11] Z Ou B Chen K H Hsieh M W Halling and P J BarrldquoExperimental and analytical investigation of concrete filledsteel tubular columnsrdquo Journal of Structural Engineeringvol 137 no 6 pp 635ndash645 2011

[12] T Perea R T Leon J F Hajjar and M D Denavit ldquoFull-scale tests of slender concrete-filled tubes axial behaviorrdquoJournal of Structural Engineering vol 139 no 7 pp 1249ndash1262 2013

[13] L H Han ldquoFlexural behavior of concrete-filled steel tubesrdquoJournal of Constructional Steel Research vol 60 no 2pp 313ndash337 2004

[14] L H Han ldquoFurther study on the flexural behavior ofconcrete-filled steel tubesrdquo Journal of Constructional SteelResearch vol 62 no 6 pp 554ndash565 2006

[15] H Lu L H Han and X L Zhao ldquoAnalytical behavior ofcircular concrete-filled thin-walled steel tubes subjected tobendingrdquoin-Walled Structures vol 47 no 3 pp 346ndash3582009

[16] C W Roeder D E Lehman and E Bishop ldquoStrength andstiffness of circular concrete-filled tubesrdquo Journal of StructuralEngineering vol 136 no 12 pp 1545ndash1553 2010

[17] J Moon C W Roeder D E Lehman and H Lee ldquoAnalyticalmodeling of bending of circular concrete-filled steel tubesrdquoEngineering Structures vol 42 pp 349ndash361 2012

[18] L H Han G H Yao and Z Tao ldquoPerformance of concrete-filled thin-walled steel tubes under pure torsionrdquoin-WalledStructures vol 45 no 1 pp 24ndash36 2007

[19] J Nie Y Wang and J Fan ldquoExperimental study on seismicbehavior of concrete filled steel tube columns under puretorsion and compressionndashtorsion cyclic loadrdquo Journal ofConstructional Steel Research vol 79 no 12 pp 115ndash1262013

[20] Y Wang J Nie and J Fan ldquo+eoretical model and in-vestigation of concrete filled steel tube columns under axial

14 Advances in Materials Science and Engineering

forcendashtorsion combined actionrdquo in-Walled Structuresvol 69 no 1 pp 1ndash9 2013

[21] American Institute of Steel Construction AISCndashLRFD MetricLoad and Resistance Factor Design Specification for StructuralSteel Buildings AISC Chicago IL USA 1994

[22] Europe en Comite de Normalisation ENV 1994ndash1ndash1 Euro-code 4mdashDesign of Composite Steel and Concrete StructuresPart 11 General Rules and Rules for Buildings CEN BrusselsBelgium 1994

[23] Brazilian Society of Standard Codes NBR 8800 Design andConstructional Details of Steel Structures of Buildings Bra-zilian Society of Standard Codes Rio de Janeiro Brazil 1986

[24] Brazilian Society of Standard Codes NBR 8800 BrazilianStandard Code Review Design and Constructional Details ofSteel and Composite Structures of Buildings BSSC BeloHorizonte Brazil 2003

[25] National Standards of the Peoplersquos Republic of China GB50936 Technical Code for Concrete Filled Steel TubularStructures National Standards of the Peoplersquos Republic ofChina Beijing China 2014 in Chinese

[26] Q Liu D Wang R Huang et al ldquoStudy on failure mode ofinland river large water level dock under ship impactrdquo PortEngineering Technology vol 47 no 4 2010 in Chinese

[27] J Xu ldquoStructural design of overhead vertical wharf for inlandriver large water levelrdquo Water Transport Engineeringvol 2006 pp 62ndash67 2006 in Chinese

[28] China Association for Engineering Construction Standardi-zation CECS 2890 Specification for Design and Constructionof Concrete-Filled Steel Tubular Structures China Associationfor Engineering Construction Standardization BeijingChina 2012 in Chinese

Advances in Materials Science and Engineering 15

CorrosionInternational Journal of

Hindawiwwwhindawicom Volume 2018

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Materials Science and EngineeringHindawiwwwhindawicom Volume 2018

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Chemistry

Analytical ChemistryInternational Journal of

Hindawiwwwhindawicom Volume 2018

ScienticaHindawiwwwhindawicom Volume 2018

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Hindawiwwwhindawicom Volume 2018

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Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom

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Volume 2018

TribologyAdvances in

Hindawiwwwhindawicom Volume 2018

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ChemistryAdvances in

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Advances inPhysical Chemistry

Hindawiwwwhindawicom Volume 2018

BioMed Research InternationalMaterials

Journal of

Hindawiwwwhindawicom Volume 2018

Na

nom

ate

ria

ls

Hindawiwwwhindawicom Volume 2018

Journal ofNanomaterials

Submit your manuscripts atwwwhindawicom

reinforced concrete specimen (RN-2) the load-displacementcurve shows a certain ductility characteristic but the ultimatebearing capacity and ultimate deformation of the specimenare signicantly smaller than the reinforced CFST compositemember

313 Strain Development In this paper the strain law of thesteel casing and concrete core under the condition of an axialcompression load is described for the specimens with a steeltube thickness of 12mm (specimen RS-A-2) and 16mm(specimen RS-B-2) During the test the vertical strain andhoop strain on the side of the steel casing were monitoredand the development rule of the compressive strain inside

the core concrete was monitored Among them four straingauges are arranged on the side of the steel casing at the topandmiddle and top of the test specimen in the circumferentialdirection and the vertical strain and lateral strain of the steelcasing at this position are measured respectively In the dataprocessing the strain values of four measuring points in thesame plane are averaged to obtain the average strain of thesteel casing at the plane e load-strain curve and averagestress-strain curve of the test piece are given below Amongthem the average stress is obtained by dividing the axial loadon the specimen by the cross-sectional area

e developments of the longitudinal strain circum-ferential strain and compression behavior of the steel tubeare shown in Figures 11ndash16 Figures 11ndash13 are laws of strain

(a) (b)

Figure 6 Failure modes of reinforced CFST pile (a) Buckling deformation (b) Splitting of the steel casing weld

1200

1000

800

600

400

200

00 2 4 6 8 10 12

RS-A-2RS-B-2

14Vertical displacement (mm)

Load

(kN

)

Figure 7 Vertical displacement-load curves of two thickness steeltube-reinforced CFST piles

1000

800

600

400

200

00 2 4 6 8 10 12

RS-A-2NS-A-2

14Vertical displacement (mm)

Load

(kN

)

Figure 8 Comparison of reinforced and unreinforced CFST pileswith thickness is 12mm

Advances in Materials Science and Engineering 7

development of specimen RS-A-2 and Figures 14ndash16 arelaws of strain development of specimen RS-B-2

From the above test results it can be seen that for thesteel casing-reinforced concrete composite member thestrain value in the middle of the specimen is slightly largerthan the top and bottom strain values e strain devel-opment of steel casings at each measuring point showselastic-plastic characteristics with the increase of load Be-fore the axial load value is less than 045 times the ultimateload of the model pile foundation the load and strain showa linear relationship while the load reaches 045 times theultimate load carrying capacity After the capacity under thesame load increment the strain increment gradually in-creases showing a nonlinear characteristic From the wholeload-strain curves of the reinforced CFST specimens itexhibited the characteristics of ductile failure

In summary the use of a steel tube plays a very im-portant role in improving the compressive deformation andmechanical properties of the components For a joint steeltube-reinforced concrete structure the bearing capacity andthe ductility of the components are greatly improvedcompared to the specimens with no steel which is due to theexistence of the internal structure of the composite structureeectively enhancing the constraints between the concreteparticles to limit the development of microcracks and theeective stress

32 Columnswith Foundation It can be seen from Figure 17that the variation in the results of the dierent model col-umns under the load at the pile top is consistent and it canbe considered that the inuence of a rockless cylinder on the

1200

1000

800

600

400

200

00 2 4 6 8 10 12

RS-B-2NS-B-2

14Vertical displacement (mm)

Load

(kN

)

Figure 9 Comparison of reinforced and unreinforced CFST piles with thickness is 16mm

1000

800

600

400

200

00 2 4 6 8 10 12

RS-A-2PL-2RN-2

14Vertical displacement (mm)

Load

(kN

)

(a)

1200

1000

800

600

400

200

00 2 4 6 8 10 12 14

Vertical displacement (mm)

Load

(kN

)

RS-B-2PL-2RN-2

(b)

Figure 10 Comparison of plain concrete reinforced concrete and reinforced CFST piles

8 Advances in Materials Science and Engineering

settlement of a rock-socketed column is also consistent Itcan be seen from Figure 17 that the displacements of Z1P1and Z1P2 are basically the same from the load values of zeroto 9 kN the load-vertical displacement curve is approxi-mately a straight line and the two piles are in the elasticstage After the load exceeds 9 kN the displacement rate ofthe Z1P1 pile exceeds that of the Z1P2 pile and the settle-ment of the pile top increases e load-vertical displace-ment curves of the two piles change slowly and the processof steep drop is not obvious Figure 17 shows several settlingsthat may be due to the inhomogeneity of the model

foundation According to the above analysis it can be seenthat the vertical bearing capacities of CFST rock-socketedpiles are weaker than those rock-socketed piles withouta steel tube the dierence is mainly because the rock-socketed pile without a steel tube has a concrete-rock in-terface with a coecurrencient of friction greater than that of theCFST rock-socketed pile with a steel-rock interface

As seen from Figure 18 the greater the rock-socketeddepth the greater the load-bearing capacity of the rock-socketed piles In addition when the depth of the pile in therock-socketed increased from 3D to 5D the vertical ultimate

1000

800

600

400

200

00 2000 4000 6000

Strain (με)8000 10000 12000

Top verticalBottom verticalCentral vertical

Load

(kN

)

(a)

50

40

30

20

Ave

rage

stre

ss (M

Pa)

10

0

Strain (με)2000

Top verticalBottom verticalCentral vertical

4000 6000 8000 10000 120000

(b)

Figure 11 Vertical strain development laws of specimen RS-A-2 with steel casing (a) Relationship of vertical strain development with load(b) Relationship of vertical strain development with average stress

1000

800

600

400

200

0 1000 2000 3000Strain (με)

4000 5000 6000 7000 8000

Load

(kN

)

Top loopBottom loopCentral loop

0

(a)

50

40

30

20

10

00 1000 2000 40003000

Strain (με)5000 6000 7000 8000

Ave

rage

stre

ss (M

Pa)

Top loopBottom loopCentral loop

(b)

Figure 12 Loop strain development of specimen RS-A-2 with steel casing (a) Relationship of loop strain development with load (b)Relationship of loop strain development with average stress

Advances in Materials Science and Engineering 9

bearing capacity increased by approximately 40 e mainreason for this eect is that with the increase in the rock-socketed depth the contact area will increase and althoughthe side friction coecurrencient does not change the total frictionof the pile will signicantly increase therefore the verticalbearing capacity of the pile is signicantly improved It isfound that the vertical ultimate bearing capacity of rock-socketed piles without a steel tube (steel-free cylinder) isapproximately 10 higher than that of the steel-retainingtube when the depth of rock-embedment is the same emain reason for this phenomenon is that the outer wall ofthe pile is very smooth since its roughness is much smallerthan the concrete the corresponding side friction is lower

and the ultimate bearing capacity of the pile is equal to thepile side friction and pile end resistance decreasing theultimate bearing capacity of the pile

4 Analysis of the Ultimate Load

According to EC4 [22] the axial load capacity (NplRd) ofa CFST column can be determined by summing the yieldload of both the steel section and concrete core Forconcrete-ned tubes of circular cross section account maybe taken of increase in strength of concrete caused byconnement provided that the relative slenderness λ doesnot exceed 0 5 and edlt 0 1 where e is the eccentricity of

0 200 400 800600 1000

Concrete

1200 1400 1600Strain (με)

500

600

700

400

300

200

100

0

Load

(kN

)

(a)

Concrete

0 200 400 800600 1000 1200 1400 1600Strain (με)

30

35

25

20

15

5

10

0

Ave

rage

stre

ss (M

Pa)

(b)

Figure 13 Axial compressive strain development of core concrete of specimen RS-A-2 (a) Relationship of vertical strain development withload (b) Relationship of vertical strain development with average stress

0 2000 4000 80006000Strain (με)

10000 12000 14000

Top vertical

Bottom verticalCentral vertical

1000

1200

800

600

400

200

0

Load

(kN

)

(a)

0 2000 4000 80006000Strain (με)

10000 12000 14000

Top verticalMiddle verticalBottom vertical

50

60

40

30

20

10

0

Ave

rage

stre

ss (M

Pa)

(b)

Figure 14 Vertical strain development laws of specimen RS-B-2 with steel casing (a) Relationship of loop strain development with load (b)Relationship of loop strain development with average stress

10 Advances in Materials Science and Engineering

loading given by MEdNEd and d is the external diameter ofthe column e plastic resistance to compression may thenbe calculated from the following expression in equations(2)ndash(5) e application of EC4 [22] is restricted to com-posite columns with steel yield stress and concrete cylinderstrength of less than 355 and 50MPa respectively efollowing presents the formulations of the AISC [21] EC4[22] NBR 8800 [23 24] and GB50396-2014 [25] standardcodes to determine the resistance capacity of axially loadedCFST columns And rs is the radius of gyration of the steelhollow section le is the length of the column Ec is themodulus of elasticity of the concrete and Es is the modulusof elasticity of the steel e formulations presented were

used to calculate the compressive strength of the axiallyloaded CFST columns investigated in the present study Inaddition the boundary conditions of the testing approachare upper if the pile is loading and lower if the pile is xed

In GB50396-2014 [25] θ means the hoop coecurrencient ofconcrete-lled steel tubular members θ αscffc αsc rep-resents the steel content of concrete-lled steel tubularmembers in the design of compressive strength of concrete-lled steel tube piles B and C are the inuence factors of thecross-sectional shape on the hoop eect and about circularcross section B 0176lowast f213 + 0974 Cminus0104fc144+ 0031 In AISC [21] the axial compression member isconsidered to be the overall stability of the member the

0 1000 2000 40003000Strain (με)

5000 6000 7000

Top loopCentral loopBottom loop

1000

1200

800

600

400

200

0

Load

(kN

)

(a)

0 1000 2000 40003000Strain (με)

5000 6000 7000

Top loopCentral loopBottom loop

50

60

40

30

20

10

0

Ave

rage

stre

ss (M

Pa)

(b)

Figure 15 Loop strain development of specimen RS-B-2 with steel casing (a) Relationship of strain development with load (b) Relationshipof strain development with average stress

0 200 400 800600 1000

Concrete

1200 1400 1600 1800Strain (με)

500

600

700

800

400

300

200

100

0

Load

(kN

)

(a)

0 200 400 800600 1000

Concrete

1200 1400 1600 1800Strain (με)

30

35

40

25

20

15

5

10

0

Ave

rage

stre

ss (M

Pa)

(b)

Figure 16 Axial compressive strain development of core concrete of specimen RS-B-2

Advances in Materials Science and Engineering 11

strength of the concrete is converted into the steel thenominal compressive strength fcr of the steel is obtained andthe bearing capacity of the concrete-lled steel tubularmember is calculated from fcr fys is the yield limit of steel fckmeans the compressive strength of concrete cylinder As isthe cross-sectional area of steel pipe Ac is the cross-sectionalarea of concrete and λc is the ratio of slenderness toslenderness In Eurocode 4 (EC4) [22] the relative slen-derness λ for the plane of bending being considered is givenby λ

NPLRkNcrradic

where NplRk is the characteristic valueof the plastic resistance to compression if instead ofthe design strengths the characteristic values are used andNcr is the elastic critical normal force for the relevantbuckling mode calculated with the eective exuralstiness (EI)c

However it should be stated that the maximum allowablevalue of diameter-thickness ratio (Dt) specied in AISC [21]is 031lowast Efy the ratio of diameter-thickness of circular-section concrete-lled steel tubular members specied inChinese specication [28] should be limited to the followingrange 20

235fy

radicleDtle 85

235fy

radic and Eurocode 4 (EC4)

[22] explicit limits the allowed Dt values in the Europeancontext to 90lowast 235fy e diameter-thickness ratio of thespecimens studied in this paper is very large exceeding theallowable range of the specications e paper attempts toestimate these specimens with large diameter-thickness ratioby using the above codes And the ultimate strength calcu-lation results of relevant specications are shown in Table 7Apparently it can be found that value of the ultimate load isgenerallymuch greater than the theoretical calculation results

25

25

20

20

Z1P1Z1P2

Load

(kN

) 15

15

10

10

5

50

0Vertical displacement (mm)

(a)

Z2P2Z2P1

25

30

20

Load

(kN

)

15

10

5

025 30 3520151050

Vertical displacement (mm)

(b)

Z3P2Z3P1

30

40

20

Load

(kN

)

10

025 30 352015

Vertical displacement (mm)1050

(c)

Figure 17 Relationship of vertical displacement and load of three depths of rock-socketed columns (a) Rock-socketed depth is 300mm (P1steel tube is 1mm P2 steel tube is 0mm) (b) Rock-socketed depth is 400mm (c) Rock-socketed depth is 500mm

12 Advances in Materials Science and Engineering

AISC [21] method

Em Es + 04EcAc

As

fmy fys + 085fckAc

As

fcr 0658λ2c( )fmy if λc le 15

fcr 0877λ2c

fmy if λc le 15

λc lcrcπ

fmy

Em( )

05

NplRd 085Asfcr

(1)

EC4 and NBR 8800 [23 24] methods

NplRd η2Asfy + Acfck 1 + η1tfy

Dfck( ) (2)

η1 η10η2 η20

(3)

η10 49minus 185 times λ + 17(λ)2 ge 0 (4)

η20 025(3 + 2λ)le 10 (5)

GB50396-2014 [25] method

N0 Ascfsc

fsc 1212 + Bθ + Cθ2( )fc

αsc As

Ac

θ αscf

fc

(6)

5 Conclusion

e present study is an attempt to study the behavior ofconcrete-lled steel tube columns subjected to axialcompression Based on the results of this study the fol-lowing conclusions can be drawn within the scope of thesetests

Table 7 e ultimate strength calculation results of relevant specications

Specimens Ultimate load (kN) NBR 8800 and EC4 (kN) AISC (kN) GB50396-2014 (kN)PL-2 406 412 419 429NS-A-2 830 493 479 560NS-B-2 885 566 535 603RN-2 560 430 416 465RS-A-2 895 493 479 596RS-B-2 1190 566 535 639PL-1 480 513 519 530NS-A-1 800 428 409 478RS-A-1 895 428 409 478RS-B-1 1125 452 474 498

35

40

45

30Load

(kN

)25

2030 35 40 45 50 55

n

P1P2

Figure 18 Relationship between n and load (n ratio of rock-socketed depth n hD)

Advances in Materials Science and Engineering 13

(1) +e reinforced CFST piles exhibit two differentfailure modes When the weld strength of the steelcasing is greater than the axial load limit of thecomposite member the failure mode is the bendingfailure caused by the local buckling deformationwhich is a ductile failure feature When the weldstrength of the steel casing is less than the axial loadlimit of the composite member the failure mode isthe open splitting of the steel casing weld under theexpansion stress of the concrete which is a brittlefailure feature

(2) +e bearing capacity of rock-socketed CFSTcolumnsis lower than that of rock-socketed columns withouta steel tube under the same conditions of a verticalload +e depth of the rock inlay is clearly affectingby the bearing capacity of the two rock-socketedcolumns and the greater the rock-socketed depththe greater the bearing capacity of the rock-socketedpiles In addition the overall sliding of the steel tubeand the core concrete of pile is small and the steeltube-concrete interface is basically in a bonding stateunder the vertical load

(3) A comparison of failure loads between the tests andthe design codes was presented+e results show thatthe provisions in EC4 [22] NBR 8800 [23 24] AISC[21] and GB50396-2014 [25]conservatively estimatethe ultimate capacities of the specimens and it can befound that value of the ultimate load is generallymuch greater than the theoretical calculation resultsSince the diameter-thickness ratio of the specimensstudied in this paper is very large exceeding theallowable range of the specifications the test resultsprovide a reference for design and performance ofthe new structure with large diameter-thicknessratio

Data Availability

+e figures and tables data used to support the findings ofthis study are included within the article

Conflicts of Interest

+e authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

+is study was financially supported by the National NaturalScience Foundation of China (nos 2011550031 and51709026) and the Western Project of China (nos2011660041 and 2011560076)

References

[1] S Jegadesh and S Jayalekshmi ldquoLoad-bearing capacity ofaxially loaded circular concrete-filled steel tubular columnsrdquoProceedings of the Institution of Civil Engineers Structures andBuildings vol 169 no 7 pp 508ndash523 2016

[2] N E Shanmugam and B Lakshmi ldquoState of the art report onsteelndashconcrete composite columnsrdquo Journal of ConstructionalResearch vol 57 no 10 pp 1041ndash1080 2001

[3] S De Nardin ldquoeoretical-experimental study high strengthconcrete-filled steel tubesrdquo MS thesis EESC-USP Sao Carlos-SP 1999 in Portuguese

[4] K Cederwall B Engstrom and M Grauers ldquoHigh-strengthconcrete used in composite columnsrdquo in Proceedings of High-Strength Concretendash2nd International Symposium pp 195ndash214Detroit MI USA 1990

[5] L Han W Li and R Bjorhovde ldquoDevelopments and ad-vanced applications of concrete-filled steel tubular (CFST)structures membersrdquo Journal of Constructional Steel Re-search vol 100 pp 211ndash228 2014

[6] L Han H Shan-Hu and F Liao ldquoPerformance and calcu-lations of concrete filled steel tubes (CFST) under axialtensionrdquo Journal of Constructional Steel Research vol 67no 11 pp 1699ndash1709 2011

[7] M A Bradford ldquoDesign strength of slender concrete filledrectangular steel tubesrdquo ACI Structural Journal vol 93 no 2pp 229ndash235 1996

[8] M D OrsquoShea and R Q Bridge ldquoDesign of thin-walledconcrete filled steel tubesrdquo Journal of Structural Engineer-ing vol 126 no 11 pp 1295ndash1303 2000

[9] B Uy ldquoLocal and postlocal buckling of fabricated steel andcomposite cross sectionsrdquo Journal of Structural Engineeringvol 127 no 6 pp 666ndash677 2001

[10] K K Choi and Y Xiao ldquoAnalytical studies of concrete-filledcircular steel tubes under axial compressionrdquo Journal ofStructural Engineering vol 136 no 5 pp 565ndash573 2010

[11] Z Ou B Chen K H Hsieh M W Halling and P J BarrldquoExperimental and analytical investigation of concrete filledsteel tubular columnsrdquo Journal of Structural Engineeringvol 137 no 6 pp 635ndash645 2011

[12] T Perea R T Leon J F Hajjar and M D Denavit ldquoFull-scale tests of slender concrete-filled tubes axial behaviorrdquoJournal of Structural Engineering vol 139 no 7 pp 1249ndash1262 2013

[13] L H Han ldquoFlexural behavior of concrete-filled steel tubesrdquoJournal of Constructional Steel Research vol 60 no 2pp 313ndash337 2004

[14] L H Han ldquoFurther study on the flexural behavior ofconcrete-filled steel tubesrdquo Journal of Constructional SteelResearch vol 62 no 6 pp 554ndash565 2006

[15] H Lu L H Han and X L Zhao ldquoAnalytical behavior ofcircular concrete-filled thin-walled steel tubes subjected tobendingrdquoin-Walled Structures vol 47 no 3 pp 346ndash3582009

[16] C W Roeder D E Lehman and E Bishop ldquoStrength andstiffness of circular concrete-filled tubesrdquo Journal of StructuralEngineering vol 136 no 12 pp 1545ndash1553 2010

[17] J Moon C W Roeder D E Lehman and H Lee ldquoAnalyticalmodeling of bending of circular concrete-filled steel tubesrdquoEngineering Structures vol 42 pp 349ndash361 2012

[18] L H Han G H Yao and Z Tao ldquoPerformance of concrete-filled thin-walled steel tubes under pure torsionrdquoin-WalledStructures vol 45 no 1 pp 24ndash36 2007

[19] J Nie Y Wang and J Fan ldquoExperimental study on seismicbehavior of concrete filled steel tube columns under puretorsion and compressionndashtorsion cyclic loadrdquo Journal ofConstructional Steel Research vol 79 no 12 pp 115ndash1262013

[20] Y Wang J Nie and J Fan ldquo+eoretical model and in-vestigation of concrete filled steel tube columns under axial

14 Advances in Materials Science and Engineering

forcendashtorsion combined actionrdquo in-Walled Structuresvol 69 no 1 pp 1ndash9 2013

[21] American Institute of Steel Construction AISCndashLRFD MetricLoad and Resistance Factor Design Specification for StructuralSteel Buildings AISC Chicago IL USA 1994

[22] Europe en Comite de Normalisation ENV 1994ndash1ndash1 Euro-code 4mdashDesign of Composite Steel and Concrete StructuresPart 11 General Rules and Rules for Buildings CEN BrusselsBelgium 1994

[23] Brazilian Society of Standard Codes NBR 8800 Design andConstructional Details of Steel Structures of Buildings Bra-zilian Society of Standard Codes Rio de Janeiro Brazil 1986

[24] Brazilian Society of Standard Codes NBR 8800 BrazilianStandard Code Review Design and Constructional Details ofSteel and Composite Structures of Buildings BSSC BeloHorizonte Brazil 2003

[25] National Standards of the Peoplersquos Republic of China GB50936 Technical Code for Concrete Filled Steel TubularStructures National Standards of the Peoplersquos Republic ofChina Beijing China 2014 in Chinese

[26] Q Liu D Wang R Huang et al ldquoStudy on failure mode ofinland river large water level dock under ship impactrdquo PortEngineering Technology vol 47 no 4 2010 in Chinese

[27] J Xu ldquoStructural design of overhead vertical wharf for inlandriver large water levelrdquo Water Transport Engineeringvol 2006 pp 62ndash67 2006 in Chinese

[28] China Association for Engineering Construction Standardi-zation CECS 2890 Specification for Design and Constructionof Concrete-Filled Steel Tubular Structures China Associationfor Engineering Construction Standardization BeijingChina 2012 in Chinese

Advances in Materials Science and Engineering 15

CorrosionInternational Journal of

Hindawiwwwhindawicom Volume 2018

Advances in

Materials Science and EngineeringHindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Journal of

Chemistry

Analytical ChemistryInternational Journal of

Hindawiwwwhindawicom Volume 2018

ScienticaHindawiwwwhindawicom Volume 2018

Polymer ScienceInternational Journal of

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Advances in Condensed Matter Physics

Hindawiwwwhindawicom Volume 2018

International Journal of

BiomaterialsHindawiwwwhindawicom

Journal ofEngineeringVolume 2018

Applied ChemistryJournal of

Hindawiwwwhindawicom Volume 2018

NanotechnologyHindawiwwwhindawicom Volume 2018

Journal of

Hindawiwwwhindawicom Volume 2018

High Energy PhysicsAdvances in

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom

The Scientific World Journal

Volume 2018

TribologyAdvances in

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

ChemistryAdvances in

Hindawiwwwhindawicom Volume 2018

Advances inPhysical Chemistry

Hindawiwwwhindawicom Volume 2018

BioMed Research InternationalMaterials

Journal of

Hindawiwwwhindawicom Volume 2018

Na

nom

ate

ria

ls

Hindawiwwwhindawicom Volume 2018

Journal ofNanomaterials

Submit your manuscripts atwwwhindawicom

development of specimen RS-A-2 and Figures 14ndash16 arelaws of strain development of specimen RS-B-2

From the above test results it can be seen that for thesteel casing-reinforced concrete composite member thestrain value in the middle of the specimen is slightly largerthan the top and bottom strain values e strain devel-opment of steel casings at each measuring point showselastic-plastic characteristics with the increase of load Be-fore the axial load value is less than 045 times the ultimateload of the model pile foundation the load and strain showa linear relationship while the load reaches 045 times theultimate load carrying capacity After the capacity under thesame load increment the strain increment gradually in-creases showing a nonlinear characteristic From the wholeload-strain curves of the reinforced CFST specimens itexhibited the characteristics of ductile failure

In summary the use of a steel tube plays a very im-portant role in improving the compressive deformation andmechanical properties of the components For a joint steeltube-reinforced concrete structure the bearing capacity andthe ductility of the components are greatly improvedcompared to the specimens with no steel which is due to theexistence of the internal structure of the composite structureeectively enhancing the constraints between the concreteparticles to limit the development of microcracks and theeective stress

32 Columnswith Foundation It can be seen from Figure 17that the variation in the results of the dierent model col-umns under the load at the pile top is consistent and it canbe considered that the inuence of a rockless cylinder on the

1200

1000

800

600

400

200

00 2 4 6 8 10 12

RS-B-2NS-B-2

14Vertical displacement (mm)

Load

(kN

)

Figure 9 Comparison of reinforced and unreinforced CFST piles with thickness is 16mm

1000

800

600

400

200

00 2 4 6 8 10 12

RS-A-2PL-2RN-2

14Vertical displacement (mm)

Load

(kN

)

(a)

1200

1000

800

600

400

200

00 2 4 6 8 10 12 14

Vertical displacement (mm)

Load

(kN

)

RS-B-2PL-2RN-2

(b)

Figure 10 Comparison of plain concrete reinforced concrete and reinforced CFST piles

8 Advances in Materials Science and Engineering

settlement of a rock-socketed column is also consistent Itcan be seen from Figure 17 that the displacements of Z1P1and Z1P2 are basically the same from the load values of zeroto 9 kN the load-vertical displacement curve is approxi-mately a straight line and the two piles are in the elasticstage After the load exceeds 9 kN the displacement rate ofthe Z1P1 pile exceeds that of the Z1P2 pile and the settle-ment of the pile top increases e load-vertical displace-ment curves of the two piles change slowly and the processof steep drop is not obvious Figure 17 shows several settlingsthat may be due to the inhomogeneity of the model

foundation According to the above analysis it can be seenthat the vertical bearing capacities of CFST rock-socketedpiles are weaker than those rock-socketed piles withouta steel tube the dierence is mainly because the rock-socketed pile without a steel tube has a concrete-rock in-terface with a coecurrencient of friction greater than that of theCFST rock-socketed pile with a steel-rock interface

As seen from Figure 18 the greater the rock-socketeddepth the greater the load-bearing capacity of the rock-socketed piles In addition when the depth of the pile in therock-socketed increased from 3D to 5D the vertical ultimate

1000

800

600

400

200

00 2000 4000 6000

Strain (με)8000 10000 12000

Top verticalBottom verticalCentral vertical

Load

(kN

)

(a)

50

40

30

20

Ave

rage

stre

ss (M

Pa)

10

0

Strain (με)2000

Top verticalBottom verticalCentral vertical

4000 6000 8000 10000 120000

(b)

Figure 11 Vertical strain development laws of specimen RS-A-2 with steel casing (a) Relationship of vertical strain development with load(b) Relationship of vertical strain development with average stress

1000

800

600

400

200

0 1000 2000 3000Strain (με)

4000 5000 6000 7000 8000

Load

(kN

)

Top loopBottom loopCentral loop

0

(a)

50

40

30

20

10

00 1000 2000 40003000

Strain (με)5000 6000 7000 8000

Ave

rage

stre

ss (M

Pa)

Top loopBottom loopCentral loop

(b)

Figure 12 Loop strain development of specimen RS-A-2 with steel casing (a) Relationship of loop strain development with load (b)Relationship of loop strain development with average stress

Advances in Materials Science and Engineering 9

bearing capacity increased by approximately 40 e mainreason for this eect is that with the increase in the rock-socketed depth the contact area will increase and althoughthe side friction coecurrencient does not change the total frictionof the pile will signicantly increase therefore the verticalbearing capacity of the pile is signicantly improved It isfound that the vertical ultimate bearing capacity of rock-socketed piles without a steel tube (steel-free cylinder) isapproximately 10 higher than that of the steel-retainingtube when the depth of rock-embedment is the same emain reason for this phenomenon is that the outer wall ofthe pile is very smooth since its roughness is much smallerthan the concrete the corresponding side friction is lower

and the ultimate bearing capacity of the pile is equal to thepile side friction and pile end resistance decreasing theultimate bearing capacity of the pile

4 Analysis of the Ultimate Load

According to EC4 [22] the axial load capacity (NplRd) ofa CFST column can be determined by summing the yieldload of both the steel section and concrete core Forconcrete-ned tubes of circular cross section account maybe taken of increase in strength of concrete caused byconnement provided that the relative slenderness λ doesnot exceed 0 5 and edlt 0 1 where e is the eccentricity of

0 200 400 800600 1000

Concrete

1200 1400 1600Strain (με)

500

600

700

400

300

200

100

0

Load

(kN

)

(a)

Concrete

0 200 400 800600 1000 1200 1400 1600Strain (με)

30

35

25

20

15

5

10

0

Ave

rage

stre

ss (M

Pa)

(b)

Figure 13 Axial compressive strain development of core concrete of specimen RS-A-2 (a) Relationship of vertical strain development withload (b) Relationship of vertical strain development with average stress

0 2000 4000 80006000Strain (με)

10000 12000 14000

Top vertical

Bottom verticalCentral vertical

1000

1200

800

600

400

200

0

Load

(kN

)

(a)

0 2000 4000 80006000Strain (με)

10000 12000 14000

Top verticalMiddle verticalBottom vertical

50

60

40

30

20

10

0

Ave

rage

stre

ss (M

Pa)

(b)

Figure 14 Vertical strain development laws of specimen RS-B-2 with steel casing (a) Relationship of loop strain development with load (b)Relationship of loop strain development with average stress

10 Advances in Materials Science and Engineering

loading given by MEdNEd and d is the external diameter ofthe column e plastic resistance to compression may thenbe calculated from the following expression in equations(2)ndash(5) e application of EC4 [22] is restricted to com-posite columns with steel yield stress and concrete cylinderstrength of less than 355 and 50MPa respectively efollowing presents the formulations of the AISC [21] EC4[22] NBR 8800 [23 24] and GB50396-2014 [25] standardcodes to determine the resistance capacity of axially loadedCFST columns And rs is the radius of gyration of the steelhollow section le is the length of the column Ec is themodulus of elasticity of the concrete and Es is the modulusof elasticity of the steel e formulations presented were

used to calculate the compressive strength of the axiallyloaded CFST columns investigated in the present study Inaddition the boundary conditions of the testing approachare upper if the pile is loading and lower if the pile is xed

In GB50396-2014 [25] θ means the hoop coecurrencient ofconcrete-lled steel tubular members θ αscffc αsc rep-resents the steel content of concrete-lled steel tubularmembers in the design of compressive strength of concrete-lled steel tube piles B and C are the inuence factors of thecross-sectional shape on the hoop eect and about circularcross section B 0176lowast f213 + 0974 Cminus0104fc144+ 0031 In AISC [21] the axial compression member isconsidered to be the overall stability of the member the

0 1000 2000 40003000Strain (με)

5000 6000 7000

Top loopCentral loopBottom loop

1000

1200

800

600

400

200

0

Load

(kN

)

(a)

0 1000 2000 40003000Strain (με)

5000 6000 7000

Top loopCentral loopBottom loop

50

60

40

30

20

10

0

Ave

rage

stre

ss (M

Pa)

(b)

Figure 15 Loop strain development of specimen RS-B-2 with steel casing (a) Relationship of strain development with load (b) Relationshipof strain development with average stress

0 200 400 800600 1000

Concrete

1200 1400 1600 1800Strain (με)

500

600

700

800

400

300

200

100

0

Load

(kN

)

(a)

0 200 400 800600 1000

Concrete

1200 1400 1600 1800Strain (με)

30

35

40

25

20

15

5

10

0

Ave

rage

stre

ss (M

Pa)

(b)

Figure 16 Axial compressive strain development of core concrete of specimen RS-B-2

Advances in Materials Science and Engineering 11

strength of the concrete is converted into the steel thenominal compressive strength fcr of the steel is obtained andthe bearing capacity of the concrete-lled steel tubularmember is calculated from fcr fys is the yield limit of steel fckmeans the compressive strength of concrete cylinder As isthe cross-sectional area of steel pipe Ac is the cross-sectionalarea of concrete and λc is the ratio of slenderness toslenderness In Eurocode 4 (EC4) [22] the relative slen-derness λ for the plane of bending being considered is givenby λ

NPLRkNcrradic

where NplRk is the characteristic valueof the plastic resistance to compression if instead ofthe design strengths the characteristic values are used andNcr is the elastic critical normal force for the relevantbuckling mode calculated with the eective exuralstiness (EI)c

However it should be stated that the maximum allowablevalue of diameter-thickness ratio (Dt) specied in AISC [21]is 031lowast Efy the ratio of diameter-thickness of circular-section concrete-lled steel tubular members specied inChinese specication [28] should be limited to the followingrange 20

235fy

radicleDtle 85

235fy

radic and Eurocode 4 (EC4)

[22] explicit limits the allowed Dt values in the Europeancontext to 90lowast 235fy e diameter-thickness ratio of thespecimens studied in this paper is very large exceeding theallowable range of the specications e paper attempts toestimate these specimens with large diameter-thickness ratioby using the above codes And the ultimate strength calcu-lation results of relevant specications are shown in Table 7Apparently it can be found that value of the ultimate load isgenerallymuch greater than the theoretical calculation results

25

25

20

20

Z1P1Z1P2

Load

(kN

) 15

15

10

10

5

50

0Vertical displacement (mm)

(a)

Z2P2Z2P1

25

30

20

Load

(kN

)

15

10

5

025 30 3520151050

Vertical displacement (mm)

(b)

Z3P2Z3P1

30

40

20

Load

(kN

)

10

025 30 352015

Vertical displacement (mm)1050

(c)

Figure 17 Relationship of vertical displacement and load of three depths of rock-socketed columns (a) Rock-socketed depth is 300mm (P1steel tube is 1mm P2 steel tube is 0mm) (b) Rock-socketed depth is 400mm (c) Rock-socketed depth is 500mm

12 Advances in Materials Science and Engineering

AISC [21] method

Em Es + 04EcAc

As

fmy fys + 085fckAc

As

fcr 0658λ2c( )fmy if λc le 15

fcr 0877λ2c

fmy if λc le 15

λc lcrcπ

fmy

Em( )

05

NplRd 085Asfcr

(1)

EC4 and NBR 8800 [23 24] methods

NplRd η2Asfy + Acfck 1 + η1tfy

Dfck( ) (2)

η1 η10η2 η20

(3)

η10 49minus 185 times λ + 17(λ)2 ge 0 (4)

η20 025(3 + 2λ)le 10 (5)

GB50396-2014 [25] method

N0 Ascfsc

fsc 1212 + Bθ + Cθ2( )fc

αsc As

Ac

θ αscf

fc

(6)

5 Conclusion

e present study is an attempt to study the behavior ofconcrete-lled steel tube columns subjected to axialcompression Based on the results of this study the fol-lowing conclusions can be drawn within the scope of thesetests

Table 7 e ultimate strength calculation results of relevant specications

Specimens Ultimate load (kN) NBR 8800 and EC4 (kN) AISC (kN) GB50396-2014 (kN)PL-2 406 412 419 429NS-A-2 830 493 479 560NS-B-2 885 566 535 603RN-2 560 430 416 465RS-A-2 895 493 479 596RS-B-2 1190 566 535 639PL-1 480 513 519 530NS-A-1 800 428 409 478RS-A-1 895 428 409 478RS-B-1 1125 452 474 498

35

40

45

30Load

(kN

)25

2030 35 40 45 50 55

n

P1P2

Figure 18 Relationship between n and load (n ratio of rock-socketed depth n hD)

Advances in Materials Science and Engineering 13

(1) +e reinforced CFST piles exhibit two differentfailure modes When the weld strength of the steelcasing is greater than the axial load limit of thecomposite member the failure mode is the bendingfailure caused by the local buckling deformationwhich is a ductile failure feature When the weldstrength of the steel casing is less than the axial loadlimit of the composite member the failure mode isthe open splitting of the steel casing weld under theexpansion stress of the concrete which is a brittlefailure feature

(2) +e bearing capacity of rock-socketed CFSTcolumnsis lower than that of rock-socketed columns withouta steel tube under the same conditions of a verticalload +e depth of the rock inlay is clearly affectingby the bearing capacity of the two rock-socketedcolumns and the greater the rock-socketed depththe greater the bearing capacity of the rock-socketedpiles In addition the overall sliding of the steel tubeand the core concrete of pile is small and the steeltube-concrete interface is basically in a bonding stateunder the vertical load

(3) A comparison of failure loads between the tests andthe design codes was presented+e results show thatthe provisions in EC4 [22] NBR 8800 [23 24] AISC[21] and GB50396-2014 [25]conservatively estimatethe ultimate capacities of the specimens and it can befound that value of the ultimate load is generallymuch greater than the theoretical calculation resultsSince the diameter-thickness ratio of the specimensstudied in this paper is very large exceeding theallowable range of the specifications the test resultsprovide a reference for design and performance ofthe new structure with large diameter-thicknessratio

Data Availability

+e figures and tables data used to support the findings ofthis study are included within the article

Conflicts of Interest

+e authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

+is study was financially supported by the National NaturalScience Foundation of China (nos 2011550031 and51709026) and the Western Project of China (nos2011660041 and 2011560076)

References

[1] S Jegadesh and S Jayalekshmi ldquoLoad-bearing capacity ofaxially loaded circular concrete-filled steel tubular columnsrdquoProceedings of the Institution of Civil Engineers Structures andBuildings vol 169 no 7 pp 508ndash523 2016

[2] N E Shanmugam and B Lakshmi ldquoState of the art report onsteelndashconcrete composite columnsrdquo Journal of ConstructionalResearch vol 57 no 10 pp 1041ndash1080 2001

[3] S De Nardin ldquoeoretical-experimental study high strengthconcrete-filled steel tubesrdquo MS thesis EESC-USP Sao Carlos-SP 1999 in Portuguese

[4] K Cederwall B Engstrom and M Grauers ldquoHigh-strengthconcrete used in composite columnsrdquo in Proceedings of High-Strength Concretendash2nd International Symposium pp 195ndash214Detroit MI USA 1990

[5] L Han W Li and R Bjorhovde ldquoDevelopments and ad-vanced applications of concrete-filled steel tubular (CFST)structures membersrdquo Journal of Constructional Steel Re-search vol 100 pp 211ndash228 2014

[6] L Han H Shan-Hu and F Liao ldquoPerformance and calcu-lations of concrete filled steel tubes (CFST) under axialtensionrdquo Journal of Constructional Steel Research vol 67no 11 pp 1699ndash1709 2011

[7] M A Bradford ldquoDesign strength of slender concrete filledrectangular steel tubesrdquo ACI Structural Journal vol 93 no 2pp 229ndash235 1996

[8] M D OrsquoShea and R Q Bridge ldquoDesign of thin-walledconcrete filled steel tubesrdquo Journal of Structural Engineer-ing vol 126 no 11 pp 1295ndash1303 2000

[9] B Uy ldquoLocal and postlocal buckling of fabricated steel andcomposite cross sectionsrdquo Journal of Structural Engineeringvol 127 no 6 pp 666ndash677 2001

[10] K K Choi and Y Xiao ldquoAnalytical studies of concrete-filledcircular steel tubes under axial compressionrdquo Journal ofStructural Engineering vol 136 no 5 pp 565ndash573 2010

[11] Z Ou B Chen K H Hsieh M W Halling and P J BarrldquoExperimental and analytical investigation of concrete filledsteel tubular columnsrdquo Journal of Structural Engineeringvol 137 no 6 pp 635ndash645 2011

[12] T Perea R T Leon J F Hajjar and M D Denavit ldquoFull-scale tests of slender concrete-filled tubes axial behaviorrdquoJournal of Structural Engineering vol 139 no 7 pp 1249ndash1262 2013

[13] L H Han ldquoFlexural behavior of concrete-filled steel tubesrdquoJournal of Constructional Steel Research vol 60 no 2pp 313ndash337 2004

[14] L H Han ldquoFurther study on the flexural behavior ofconcrete-filled steel tubesrdquo Journal of Constructional SteelResearch vol 62 no 6 pp 554ndash565 2006

[15] H Lu L H Han and X L Zhao ldquoAnalytical behavior ofcircular concrete-filled thin-walled steel tubes subjected tobendingrdquoin-Walled Structures vol 47 no 3 pp 346ndash3582009

[16] C W Roeder D E Lehman and E Bishop ldquoStrength andstiffness of circular concrete-filled tubesrdquo Journal of StructuralEngineering vol 136 no 12 pp 1545ndash1553 2010

[17] J Moon C W Roeder D E Lehman and H Lee ldquoAnalyticalmodeling of bending of circular concrete-filled steel tubesrdquoEngineering Structures vol 42 pp 349ndash361 2012

[18] L H Han G H Yao and Z Tao ldquoPerformance of concrete-filled thin-walled steel tubes under pure torsionrdquoin-WalledStructures vol 45 no 1 pp 24ndash36 2007

[19] J Nie Y Wang and J Fan ldquoExperimental study on seismicbehavior of concrete filled steel tube columns under puretorsion and compressionndashtorsion cyclic loadrdquo Journal ofConstructional Steel Research vol 79 no 12 pp 115ndash1262013

[20] Y Wang J Nie and J Fan ldquo+eoretical model and in-vestigation of concrete filled steel tube columns under axial

14 Advances in Materials Science and Engineering

forcendashtorsion combined actionrdquo in-Walled Structuresvol 69 no 1 pp 1ndash9 2013

[21] American Institute of Steel Construction AISCndashLRFD MetricLoad and Resistance Factor Design Specification for StructuralSteel Buildings AISC Chicago IL USA 1994

[22] Europe en Comite de Normalisation ENV 1994ndash1ndash1 Euro-code 4mdashDesign of Composite Steel and Concrete StructuresPart 11 General Rules and Rules for Buildings CEN BrusselsBelgium 1994

[23] Brazilian Society of Standard Codes NBR 8800 Design andConstructional Details of Steel Structures of Buildings Bra-zilian Society of Standard Codes Rio de Janeiro Brazil 1986

[24] Brazilian Society of Standard Codes NBR 8800 BrazilianStandard Code Review Design and Constructional Details ofSteel and Composite Structures of Buildings BSSC BeloHorizonte Brazil 2003

[25] National Standards of the Peoplersquos Republic of China GB50936 Technical Code for Concrete Filled Steel TubularStructures National Standards of the Peoplersquos Republic ofChina Beijing China 2014 in Chinese

[26] Q Liu D Wang R Huang et al ldquoStudy on failure mode ofinland river large water level dock under ship impactrdquo PortEngineering Technology vol 47 no 4 2010 in Chinese

[27] J Xu ldquoStructural design of overhead vertical wharf for inlandriver large water levelrdquo Water Transport Engineeringvol 2006 pp 62ndash67 2006 in Chinese

[28] China Association for Engineering Construction Standardi-zation CECS 2890 Specification for Design and Constructionof Concrete-Filled Steel Tubular Structures China Associationfor Engineering Construction Standardization BeijingChina 2012 in Chinese

Advances in Materials Science and Engineering 15

CorrosionInternational Journal of

Hindawiwwwhindawicom Volume 2018

Advances in

Materials Science and EngineeringHindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Journal of

Chemistry

Analytical ChemistryInternational Journal of

Hindawiwwwhindawicom Volume 2018

ScienticaHindawiwwwhindawicom Volume 2018

Polymer ScienceInternational Journal of

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Advances in Condensed Matter Physics

Hindawiwwwhindawicom Volume 2018

International Journal of

BiomaterialsHindawiwwwhindawicom

Journal ofEngineeringVolume 2018

Applied ChemistryJournal of

Hindawiwwwhindawicom Volume 2018

NanotechnologyHindawiwwwhindawicom Volume 2018

Journal of

Hindawiwwwhindawicom Volume 2018

High Energy PhysicsAdvances in

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom

The Scientific World Journal

Volume 2018

TribologyAdvances in

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

ChemistryAdvances in

Hindawiwwwhindawicom Volume 2018

Advances inPhysical Chemistry

Hindawiwwwhindawicom Volume 2018

BioMed Research InternationalMaterials

Journal of

Hindawiwwwhindawicom Volume 2018

Na

nom

ate

ria

ls

Hindawiwwwhindawicom Volume 2018

Journal ofNanomaterials

Submit your manuscripts atwwwhindawicom

settlement of a rock-socketed column is also consistent Itcan be seen from Figure 17 that the displacements of Z1P1and Z1P2 are basically the same from the load values of zeroto 9 kN the load-vertical displacement curve is approxi-mately a straight line and the two piles are in the elasticstage After the load exceeds 9 kN the displacement rate ofthe Z1P1 pile exceeds that of the Z1P2 pile and the settle-ment of the pile top increases e load-vertical displace-ment curves of the two piles change slowly and the processof steep drop is not obvious Figure 17 shows several settlingsthat may be due to the inhomogeneity of the model

foundation According to the above analysis it can be seenthat the vertical bearing capacities of CFST rock-socketedpiles are weaker than those rock-socketed piles withouta steel tube the dierence is mainly because the rock-socketed pile without a steel tube has a concrete-rock in-terface with a coecurrencient of friction greater than that of theCFST rock-socketed pile with a steel-rock interface

As seen from Figure 18 the greater the rock-socketeddepth the greater the load-bearing capacity of the rock-socketed piles In addition when the depth of the pile in therock-socketed increased from 3D to 5D the vertical ultimate

1000

800

600

400

200

00 2000 4000 6000

Strain (με)8000 10000 12000

Top verticalBottom verticalCentral vertical

Load

(kN

)

(a)

50

40

30

20

Ave

rage

stre

ss (M

Pa)

10

0

Strain (με)2000

Top verticalBottom verticalCentral vertical

4000 6000 8000 10000 120000

(b)

Figure 11 Vertical strain development laws of specimen RS-A-2 with steel casing (a) Relationship of vertical strain development with load(b) Relationship of vertical strain development with average stress

1000

800

600

400

200

0 1000 2000 3000Strain (με)

4000 5000 6000 7000 8000

Load

(kN

)

Top loopBottom loopCentral loop

0

(a)

50

40

30

20

10

00 1000 2000 40003000

Strain (με)5000 6000 7000 8000

Ave

rage

stre

ss (M

Pa)

Top loopBottom loopCentral loop

(b)

Figure 12 Loop strain development of specimen RS-A-2 with steel casing (a) Relationship of loop strain development with load (b)Relationship of loop strain development with average stress

Advances in Materials Science and Engineering 9

bearing capacity increased by approximately 40 e mainreason for this eect is that with the increase in the rock-socketed depth the contact area will increase and althoughthe side friction coecurrencient does not change the total frictionof the pile will signicantly increase therefore the verticalbearing capacity of the pile is signicantly improved It isfound that the vertical ultimate bearing capacity of rock-socketed piles without a steel tube (steel-free cylinder) isapproximately 10 higher than that of the steel-retainingtube when the depth of rock-embedment is the same emain reason for this phenomenon is that the outer wall ofthe pile is very smooth since its roughness is much smallerthan the concrete the corresponding side friction is lower

and the ultimate bearing capacity of the pile is equal to thepile side friction and pile end resistance decreasing theultimate bearing capacity of the pile

4 Analysis of the Ultimate Load

According to EC4 [22] the axial load capacity (NplRd) ofa CFST column can be determined by summing the yieldload of both the steel section and concrete core Forconcrete-ned tubes of circular cross section account maybe taken of increase in strength of concrete caused byconnement provided that the relative slenderness λ doesnot exceed 0 5 and edlt 0 1 where e is the eccentricity of

0 200 400 800600 1000

Concrete

1200 1400 1600Strain (με)

500

600

700

400

300

200

100

0

Load

(kN

)

(a)

Concrete

0 200 400 800600 1000 1200 1400 1600Strain (με)

30

35

25

20

15

5

10

0

Ave

rage

stre

ss (M

Pa)

(b)

Figure 13 Axial compressive strain development of core concrete of specimen RS-A-2 (a) Relationship of vertical strain development withload (b) Relationship of vertical strain development with average stress

0 2000 4000 80006000Strain (με)

10000 12000 14000

Top vertical

Bottom verticalCentral vertical

1000

1200

800

600

400

200

0

Load

(kN

)

(a)

0 2000 4000 80006000Strain (με)

10000 12000 14000

Top verticalMiddle verticalBottom vertical

50

60

40

30

20

10

0

Ave

rage

stre

ss (M

Pa)

(b)

Figure 14 Vertical strain development laws of specimen RS-B-2 with steel casing (a) Relationship of loop strain development with load (b)Relationship of loop strain development with average stress

10 Advances in Materials Science and Engineering

loading given by MEdNEd and d is the external diameter ofthe column e plastic resistance to compression may thenbe calculated from the following expression in equations(2)ndash(5) e application of EC4 [22] is restricted to com-posite columns with steel yield stress and concrete cylinderstrength of less than 355 and 50MPa respectively efollowing presents the formulations of the AISC [21] EC4[22] NBR 8800 [23 24] and GB50396-2014 [25] standardcodes to determine the resistance capacity of axially loadedCFST columns And rs is the radius of gyration of the steelhollow section le is the length of the column Ec is themodulus of elasticity of the concrete and Es is the modulusof elasticity of the steel e formulations presented were

used to calculate the compressive strength of the axiallyloaded CFST columns investigated in the present study Inaddition the boundary conditions of the testing approachare upper if the pile is loading and lower if the pile is xed

In GB50396-2014 [25] θ means the hoop coecurrencient ofconcrete-lled steel tubular members θ αscffc αsc rep-resents the steel content of concrete-lled steel tubularmembers in the design of compressive strength of concrete-lled steel tube piles B and C are the inuence factors of thecross-sectional shape on the hoop eect and about circularcross section B 0176lowast f213 + 0974 Cminus0104fc144+ 0031 In AISC [21] the axial compression member isconsidered to be the overall stability of the member the

0 1000 2000 40003000Strain (με)

5000 6000 7000

Top loopCentral loopBottom loop

1000

1200

800

600

400

200

0

Load

(kN

)

(a)

0 1000 2000 40003000Strain (με)

5000 6000 7000

Top loopCentral loopBottom loop

50

60

40

30

20

10

0

Ave

rage

stre

ss (M

Pa)

(b)

Figure 15 Loop strain development of specimen RS-B-2 with steel casing (a) Relationship of strain development with load (b) Relationshipof strain development with average stress

0 200 400 800600 1000

Concrete

1200 1400 1600 1800Strain (με)

500

600

700

800

400

300

200

100

0

Load

(kN

)

(a)

0 200 400 800600 1000

Concrete

1200 1400 1600 1800Strain (με)

30

35

40

25

20

15

5

10

0

Ave

rage

stre

ss (M

Pa)

(b)

Figure 16 Axial compressive strain development of core concrete of specimen RS-B-2

Advances in Materials Science and Engineering 11

strength of the concrete is converted into the steel thenominal compressive strength fcr of the steel is obtained andthe bearing capacity of the concrete-lled steel tubularmember is calculated from fcr fys is the yield limit of steel fckmeans the compressive strength of concrete cylinder As isthe cross-sectional area of steel pipe Ac is the cross-sectionalarea of concrete and λc is the ratio of slenderness toslenderness In Eurocode 4 (EC4) [22] the relative slen-derness λ for the plane of bending being considered is givenby λ

NPLRkNcrradic

where NplRk is the characteristic valueof the plastic resistance to compression if instead ofthe design strengths the characteristic values are used andNcr is the elastic critical normal force for the relevantbuckling mode calculated with the eective exuralstiness (EI)c

However it should be stated that the maximum allowablevalue of diameter-thickness ratio (Dt) specied in AISC [21]is 031lowast Efy the ratio of diameter-thickness of circular-section concrete-lled steel tubular members specied inChinese specication [28] should be limited to the followingrange 20

235fy

radicleDtle 85

235fy

radic and Eurocode 4 (EC4)

[22] explicit limits the allowed Dt values in the Europeancontext to 90lowast 235fy e diameter-thickness ratio of thespecimens studied in this paper is very large exceeding theallowable range of the specications e paper attempts toestimate these specimens with large diameter-thickness ratioby using the above codes And the ultimate strength calcu-lation results of relevant specications are shown in Table 7Apparently it can be found that value of the ultimate load isgenerallymuch greater than the theoretical calculation results

25

25

20

20

Z1P1Z1P2

Load

(kN

) 15

15

10

10

5

50

0Vertical displacement (mm)

(a)

Z2P2Z2P1

25

30

20

Load

(kN

)

15

10

5

025 30 3520151050

Vertical displacement (mm)

(b)

Z3P2Z3P1

30

40

20

Load

(kN

)

10

025 30 352015

Vertical displacement (mm)1050

(c)

Figure 17 Relationship of vertical displacement and load of three depths of rock-socketed columns (a) Rock-socketed depth is 300mm (P1steel tube is 1mm P2 steel tube is 0mm) (b) Rock-socketed depth is 400mm (c) Rock-socketed depth is 500mm

12 Advances in Materials Science and Engineering

AISC [21] method

Em Es + 04EcAc

As

fmy fys + 085fckAc

As

fcr 0658λ2c( )fmy if λc le 15

fcr 0877λ2c

fmy if λc le 15

λc lcrcπ

fmy

Em( )

05

NplRd 085Asfcr

(1)

EC4 and NBR 8800 [23 24] methods

NplRd η2Asfy + Acfck 1 + η1tfy

Dfck( ) (2)

η1 η10η2 η20

(3)

η10 49minus 185 times λ + 17(λ)2 ge 0 (4)

η20 025(3 + 2λ)le 10 (5)

GB50396-2014 [25] method

N0 Ascfsc

fsc 1212 + Bθ + Cθ2( )fc

αsc As

Ac

θ αscf

fc

(6)

5 Conclusion

e present study is an attempt to study the behavior ofconcrete-lled steel tube columns subjected to axialcompression Based on the results of this study the fol-lowing conclusions can be drawn within the scope of thesetests

Table 7 e ultimate strength calculation results of relevant specications

Specimens Ultimate load (kN) NBR 8800 and EC4 (kN) AISC (kN) GB50396-2014 (kN)PL-2 406 412 419 429NS-A-2 830 493 479 560NS-B-2 885 566 535 603RN-2 560 430 416 465RS-A-2 895 493 479 596RS-B-2 1190 566 535 639PL-1 480 513 519 530NS-A-1 800 428 409 478RS-A-1 895 428 409 478RS-B-1 1125 452 474 498

35

40

45

30Load

(kN

)25

2030 35 40 45 50 55

n

P1P2

Figure 18 Relationship between n and load (n ratio of rock-socketed depth n hD)

Advances in Materials Science and Engineering 13

(1) +e reinforced CFST piles exhibit two differentfailure modes When the weld strength of the steelcasing is greater than the axial load limit of thecomposite member the failure mode is the bendingfailure caused by the local buckling deformationwhich is a ductile failure feature When the weldstrength of the steel casing is less than the axial loadlimit of the composite member the failure mode isthe open splitting of the steel casing weld under theexpansion stress of the concrete which is a brittlefailure feature

(2) +e bearing capacity of rock-socketed CFSTcolumnsis lower than that of rock-socketed columns withouta steel tube under the same conditions of a verticalload +e depth of the rock inlay is clearly affectingby the bearing capacity of the two rock-socketedcolumns and the greater the rock-socketed depththe greater the bearing capacity of the rock-socketedpiles In addition the overall sliding of the steel tubeand the core concrete of pile is small and the steeltube-concrete interface is basically in a bonding stateunder the vertical load

(3) A comparison of failure loads between the tests andthe design codes was presented+e results show thatthe provisions in EC4 [22] NBR 8800 [23 24] AISC[21] and GB50396-2014 [25]conservatively estimatethe ultimate capacities of the specimens and it can befound that value of the ultimate load is generallymuch greater than the theoretical calculation resultsSince the diameter-thickness ratio of the specimensstudied in this paper is very large exceeding theallowable range of the specifications the test resultsprovide a reference for design and performance ofthe new structure with large diameter-thicknessratio

Data Availability

+e figures and tables data used to support the findings ofthis study are included within the article

Conflicts of Interest

+e authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

+is study was financially supported by the National NaturalScience Foundation of China (nos 2011550031 and51709026) and the Western Project of China (nos2011660041 and 2011560076)

References

[1] S Jegadesh and S Jayalekshmi ldquoLoad-bearing capacity ofaxially loaded circular concrete-filled steel tubular columnsrdquoProceedings of the Institution of Civil Engineers Structures andBuildings vol 169 no 7 pp 508ndash523 2016

[2] N E Shanmugam and B Lakshmi ldquoState of the art report onsteelndashconcrete composite columnsrdquo Journal of ConstructionalResearch vol 57 no 10 pp 1041ndash1080 2001

[3] S De Nardin ldquoeoretical-experimental study high strengthconcrete-filled steel tubesrdquo MS thesis EESC-USP Sao Carlos-SP 1999 in Portuguese

[4] K Cederwall B Engstrom and M Grauers ldquoHigh-strengthconcrete used in composite columnsrdquo in Proceedings of High-Strength Concretendash2nd International Symposium pp 195ndash214Detroit MI USA 1990

[5] L Han W Li and R Bjorhovde ldquoDevelopments and ad-vanced applications of concrete-filled steel tubular (CFST)structures membersrdquo Journal of Constructional Steel Re-search vol 100 pp 211ndash228 2014

[6] L Han H Shan-Hu and F Liao ldquoPerformance and calcu-lations of concrete filled steel tubes (CFST) under axialtensionrdquo Journal of Constructional Steel Research vol 67no 11 pp 1699ndash1709 2011

[7] M A Bradford ldquoDesign strength of slender concrete filledrectangular steel tubesrdquo ACI Structural Journal vol 93 no 2pp 229ndash235 1996

[8] M D OrsquoShea and R Q Bridge ldquoDesign of thin-walledconcrete filled steel tubesrdquo Journal of Structural Engineer-ing vol 126 no 11 pp 1295ndash1303 2000

[9] B Uy ldquoLocal and postlocal buckling of fabricated steel andcomposite cross sectionsrdquo Journal of Structural Engineeringvol 127 no 6 pp 666ndash677 2001

[10] K K Choi and Y Xiao ldquoAnalytical studies of concrete-filledcircular steel tubes under axial compressionrdquo Journal ofStructural Engineering vol 136 no 5 pp 565ndash573 2010

[11] Z Ou B Chen K H Hsieh M W Halling and P J BarrldquoExperimental and analytical investigation of concrete filledsteel tubular columnsrdquo Journal of Structural Engineeringvol 137 no 6 pp 635ndash645 2011

[12] T Perea R T Leon J F Hajjar and M D Denavit ldquoFull-scale tests of slender concrete-filled tubes axial behaviorrdquoJournal of Structural Engineering vol 139 no 7 pp 1249ndash1262 2013

[13] L H Han ldquoFlexural behavior of concrete-filled steel tubesrdquoJournal of Constructional Steel Research vol 60 no 2pp 313ndash337 2004

[14] L H Han ldquoFurther study on the flexural behavior ofconcrete-filled steel tubesrdquo Journal of Constructional SteelResearch vol 62 no 6 pp 554ndash565 2006

[15] H Lu L H Han and X L Zhao ldquoAnalytical behavior ofcircular concrete-filled thin-walled steel tubes subjected tobendingrdquoin-Walled Structures vol 47 no 3 pp 346ndash3582009

[16] C W Roeder D E Lehman and E Bishop ldquoStrength andstiffness of circular concrete-filled tubesrdquo Journal of StructuralEngineering vol 136 no 12 pp 1545ndash1553 2010

[17] J Moon C W Roeder D E Lehman and H Lee ldquoAnalyticalmodeling of bending of circular concrete-filled steel tubesrdquoEngineering Structures vol 42 pp 349ndash361 2012

[18] L H Han G H Yao and Z Tao ldquoPerformance of concrete-filled thin-walled steel tubes under pure torsionrdquoin-WalledStructures vol 45 no 1 pp 24ndash36 2007

[19] J Nie Y Wang and J Fan ldquoExperimental study on seismicbehavior of concrete filled steel tube columns under puretorsion and compressionndashtorsion cyclic loadrdquo Journal ofConstructional Steel Research vol 79 no 12 pp 115ndash1262013

[20] Y Wang J Nie and J Fan ldquo+eoretical model and in-vestigation of concrete filled steel tube columns under axial

14 Advances in Materials Science and Engineering

forcendashtorsion combined actionrdquo in-Walled Structuresvol 69 no 1 pp 1ndash9 2013

[21] American Institute of Steel Construction AISCndashLRFD MetricLoad and Resistance Factor Design Specification for StructuralSteel Buildings AISC Chicago IL USA 1994

[22] Europe en Comite de Normalisation ENV 1994ndash1ndash1 Euro-code 4mdashDesign of Composite Steel and Concrete StructuresPart 11 General Rules and Rules for Buildings CEN BrusselsBelgium 1994

[23] Brazilian Society of Standard Codes NBR 8800 Design andConstructional Details of Steel Structures of Buildings Bra-zilian Society of Standard Codes Rio de Janeiro Brazil 1986

[24] Brazilian Society of Standard Codes NBR 8800 BrazilianStandard Code Review Design and Constructional Details ofSteel and Composite Structures of Buildings BSSC BeloHorizonte Brazil 2003

[25] National Standards of the Peoplersquos Republic of China GB50936 Technical Code for Concrete Filled Steel TubularStructures National Standards of the Peoplersquos Republic ofChina Beijing China 2014 in Chinese

[26] Q Liu D Wang R Huang et al ldquoStudy on failure mode ofinland river large water level dock under ship impactrdquo PortEngineering Technology vol 47 no 4 2010 in Chinese

[27] J Xu ldquoStructural design of overhead vertical wharf for inlandriver large water levelrdquo Water Transport Engineeringvol 2006 pp 62ndash67 2006 in Chinese

[28] China Association for Engineering Construction Standardi-zation CECS 2890 Specification for Design and Constructionof Concrete-Filled Steel Tubular Structures China Associationfor Engineering Construction Standardization BeijingChina 2012 in Chinese

Advances in Materials Science and Engineering 15

CorrosionInternational Journal of

Hindawiwwwhindawicom Volume 2018

Advances in

Materials Science and EngineeringHindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Journal of

Chemistry

Analytical ChemistryInternational Journal of

Hindawiwwwhindawicom Volume 2018

ScienticaHindawiwwwhindawicom Volume 2018

Polymer ScienceInternational Journal of

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Advances in Condensed Matter Physics

Hindawiwwwhindawicom Volume 2018

International Journal of

BiomaterialsHindawiwwwhindawicom

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Applied ChemistryJournal of

Hindawiwwwhindawicom Volume 2018

NanotechnologyHindawiwwwhindawicom Volume 2018

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Hindawiwwwhindawicom Volume 2018

High Energy PhysicsAdvances in

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom

The Scientific World Journal

Volume 2018

TribologyAdvances in

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

ChemistryAdvances in

Hindawiwwwhindawicom Volume 2018

Advances inPhysical Chemistry

Hindawiwwwhindawicom Volume 2018

BioMed Research InternationalMaterials

Journal of

Hindawiwwwhindawicom Volume 2018

Na

nom

ate

ria

ls

Hindawiwwwhindawicom Volume 2018

Journal ofNanomaterials

Submit your manuscripts atwwwhindawicom

bearing capacity increased by approximately 40 e mainreason for this eect is that with the increase in the rock-socketed depth the contact area will increase and althoughthe side friction coecurrencient does not change the total frictionof the pile will signicantly increase therefore the verticalbearing capacity of the pile is signicantly improved It isfound that the vertical ultimate bearing capacity of rock-socketed piles without a steel tube (steel-free cylinder) isapproximately 10 higher than that of the steel-retainingtube when the depth of rock-embedment is the same emain reason for this phenomenon is that the outer wall ofthe pile is very smooth since its roughness is much smallerthan the concrete the corresponding side friction is lower

and the ultimate bearing capacity of the pile is equal to thepile side friction and pile end resistance decreasing theultimate bearing capacity of the pile

4 Analysis of the Ultimate Load

According to EC4 [22] the axial load capacity (NplRd) ofa CFST column can be determined by summing the yieldload of both the steel section and concrete core Forconcrete-ned tubes of circular cross section account maybe taken of increase in strength of concrete caused byconnement provided that the relative slenderness λ doesnot exceed 0 5 and edlt 0 1 where e is the eccentricity of

0 200 400 800600 1000

Concrete

1200 1400 1600Strain (με)

500

600

700

400

300

200

100

0

Load

(kN

)

(a)

Concrete

0 200 400 800600 1000 1200 1400 1600Strain (με)

30

35

25

20

15

5

10

0

Ave

rage

stre

ss (M

Pa)

(b)

Figure 13 Axial compressive strain development of core concrete of specimen RS-A-2 (a) Relationship of vertical strain development withload (b) Relationship of vertical strain development with average stress

0 2000 4000 80006000Strain (με)

10000 12000 14000

Top vertical

Bottom verticalCentral vertical

1000

1200

800

600

400

200

0

Load

(kN

)

(a)

0 2000 4000 80006000Strain (με)

10000 12000 14000

Top verticalMiddle verticalBottom vertical

50

60

40

30

20

10

0

Ave

rage

stre

ss (M

Pa)

(b)

Figure 14 Vertical strain development laws of specimen RS-B-2 with steel casing (a) Relationship of loop strain development with load (b)Relationship of loop strain development with average stress

10 Advances in Materials Science and Engineering

loading given by MEdNEd and d is the external diameter ofthe column e plastic resistance to compression may thenbe calculated from the following expression in equations(2)ndash(5) e application of EC4 [22] is restricted to com-posite columns with steel yield stress and concrete cylinderstrength of less than 355 and 50MPa respectively efollowing presents the formulations of the AISC [21] EC4[22] NBR 8800 [23 24] and GB50396-2014 [25] standardcodes to determine the resistance capacity of axially loadedCFST columns And rs is the radius of gyration of the steelhollow section le is the length of the column Ec is themodulus of elasticity of the concrete and Es is the modulusof elasticity of the steel e formulations presented were

used to calculate the compressive strength of the axiallyloaded CFST columns investigated in the present study Inaddition the boundary conditions of the testing approachare upper if the pile is loading and lower if the pile is xed

In GB50396-2014 [25] θ means the hoop coecurrencient ofconcrete-lled steel tubular members θ αscffc αsc rep-resents the steel content of concrete-lled steel tubularmembers in the design of compressive strength of concrete-lled steel tube piles B and C are the inuence factors of thecross-sectional shape on the hoop eect and about circularcross section B 0176lowast f213 + 0974 Cminus0104fc144+ 0031 In AISC [21] the axial compression member isconsidered to be the overall stability of the member the

0 1000 2000 40003000Strain (με)

5000 6000 7000

Top loopCentral loopBottom loop

1000

1200

800

600

400

200

0

Load

(kN

)

(a)

0 1000 2000 40003000Strain (με)

5000 6000 7000

Top loopCentral loopBottom loop

50

60

40

30

20

10

0

Ave

rage

stre

ss (M

Pa)

(b)

Figure 15 Loop strain development of specimen RS-B-2 with steel casing (a) Relationship of strain development with load (b) Relationshipof strain development with average stress

0 200 400 800600 1000

Concrete

1200 1400 1600 1800Strain (με)

500

600

700

800

400

300

200

100

0

Load

(kN

)

(a)

0 200 400 800600 1000

Concrete

1200 1400 1600 1800Strain (με)

30

35

40

25

20

15

5

10

0

Ave

rage

stre

ss (M

Pa)

(b)

Figure 16 Axial compressive strain development of core concrete of specimen RS-B-2

Advances in Materials Science and Engineering 11

strength of the concrete is converted into the steel thenominal compressive strength fcr of the steel is obtained andthe bearing capacity of the concrete-lled steel tubularmember is calculated from fcr fys is the yield limit of steel fckmeans the compressive strength of concrete cylinder As isthe cross-sectional area of steel pipe Ac is the cross-sectionalarea of concrete and λc is the ratio of slenderness toslenderness In Eurocode 4 (EC4) [22] the relative slen-derness λ for the plane of bending being considered is givenby λ

NPLRkNcrradic

where NplRk is the characteristic valueof the plastic resistance to compression if instead ofthe design strengths the characteristic values are used andNcr is the elastic critical normal force for the relevantbuckling mode calculated with the eective exuralstiness (EI)c

However it should be stated that the maximum allowablevalue of diameter-thickness ratio (Dt) specied in AISC [21]is 031lowast Efy the ratio of diameter-thickness of circular-section concrete-lled steel tubular members specied inChinese specication [28] should be limited to the followingrange 20

235fy

radicleDtle 85

235fy

radic and Eurocode 4 (EC4)

[22] explicit limits the allowed Dt values in the Europeancontext to 90lowast 235fy e diameter-thickness ratio of thespecimens studied in this paper is very large exceeding theallowable range of the specications e paper attempts toestimate these specimens with large diameter-thickness ratioby using the above codes And the ultimate strength calcu-lation results of relevant specications are shown in Table 7Apparently it can be found that value of the ultimate load isgenerallymuch greater than the theoretical calculation results

25

25

20

20

Z1P1Z1P2

Load

(kN

) 15

15

10

10

5

50

0Vertical displacement (mm)

(a)

Z2P2Z2P1

25

30

20

Load

(kN

)

15

10

5

025 30 3520151050

Vertical displacement (mm)

(b)

Z3P2Z3P1

30

40

20

Load

(kN

)

10

025 30 352015

Vertical displacement (mm)1050

(c)

Figure 17 Relationship of vertical displacement and load of three depths of rock-socketed columns (a) Rock-socketed depth is 300mm (P1steel tube is 1mm P2 steel tube is 0mm) (b) Rock-socketed depth is 400mm (c) Rock-socketed depth is 500mm

12 Advances in Materials Science and Engineering

AISC [21] method

Em Es + 04EcAc

As

fmy fys + 085fckAc

As

fcr 0658λ2c( )fmy if λc le 15

fcr 0877λ2c

fmy if λc le 15

λc lcrcπ

fmy

Em( )

05

NplRd 085Asfcr

(1)

EC4 and NBR 8800 [23 24] methods

NplRd η2Asfy + Acfck 1 + η1tfy

Dfck( ) (2)

η1 η10η2 η20

(3)

η10 49minus 185 times λ + 17(λ)2 ge 0 (4)

η20 025(3 + 2λ)le 10 (5)

GB50396-2014 [25] method

N0 Ascfsc

fsc 1212 + Bθ + Cθ2( )fc

αsc As

Ac

θ αscf

fc

(6)

5 Conclusion

e present study is an attempt to study the behavior ofconcrete-lled steel tube columns subjected to axialcompression Based on the results of this study the fol-lowing conclusions can be drawn within the scope of thesetests

Table 7 e ultimate strength calculation results of relevant specications

Specimens Ultimate load (kN) NBR 8800 and EC4 (kN) AISC (kN) GB50396-2014 (kN)PL-2 406 412 419 429NS-A-2 830 493 479 560NS-B-2 885 566 535 603RN-2 560 430 416 465RS-A-2 895 493 479 596RS-B-2 1190 566 535 639PL-1 480 513 519 530NS-A-1 800 428 409 478RS-A-1 895 428 409 478RS-B-1 1125 452 474 498

35

40

45

30Load

(kN

)25

2030 35 40 45 50 55

n

P1P2

Figure 18 Relationship between n and load (n ratio of rock-socketed depth n hD)

Advances in Materials Science and Engineering 13

(1) +e reinforced CFST piles exhibit two differentfailure modes When the weld strength of the steelcasing is greater than the axial load limit of thecomposite member the failure mode is the bendingfailure caused by the local buckling deformationwhich is a ductile failure feature When the weldstrength of the steel casing is less than the axial loadlimit of the composite member the failure mode isthe open splitting of the steel casing weld under theexpansion stress of the concrete which is a brittlefailure feature

(2) +e bearing capacity of rock-socketed CFSTcolumnsis lower than that of rock-socketed columns withouta steel tube under the same conditions of a verticalload +e depth of the rock inlay is clearly affectingby the bearing capacity of the two rock-socketedcolumns and the greater the rock-socketed depththe greater the bearing capacity of the rock-socketedpiles In addition the overall sliding of the steel tubeand the core concrete of pile is small and the steeltube-concrete interface is basically in a bonding stateunder the vertical load

(3) A comparison of failure loads between the tests andthe design codes was presented+e results show thatthe provisions in EC4 [22] NBR 8800 [23 24] AISC[21] and GB50396-2014 [25]conservatively estimatethe ultimate capacities of the specimens and it can befound that value of the ultimate load is generallymuch greater than the theoretical calculation resultsSince the diameter-thickness ratio of the specimensstudied in this paper is very large exceeding theallowable range of the specifications the test resultsprovide a reference for design and performance ofthe new structure with large diameter-thicknessratio

Data Availability

+e figures and tables data used to support the findings ofthis study are included within the article

Conflicts of Interest

+e authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

+is study was financially supported by the National NaturalScience Foundation of China (nos 2011550031 and51709026) and the Western Project of China (nos2011660041 and 2011560076)

References

[1] S Jegadesh and S Jayalekshmi ldquoLoad-bearing capacity ofaxially loaded circular concrete-filled steel tubular columnsrdquoProceedings of the Institution of Civil Engineers Structures andBuildings vol 169 no 7 pp 508ndash523 2016

[2] N E Shanmugam and B Lakshmi ldquoState of the art report onsteelndashconcrete composite columnsrdquo Journal of ConstructionalResearch vol 57 no 10 pp 1041ndash1080 2001

[3] S De Nardin ldquoeoretical-experimental study high strengthconcrete-filled steel tubesrdquo MS thesis EESC-USP Sao Carlos-SP 1999 in Portuguese

[4] K Cederwall B Engstrom and M Grauers ldquoHigh-strengthconcrete used in composite columnsrdquo in Proceedings of High-Strength Concretendash2nd International Symposium pp 195ndash214Detroit MI USA 1990

[5] L Han W Li and R Bjorhovde ldquoDevelopments and ad-vanced applications of concrete-filled steel tubular (CFST)structures membersrdquo Journal of Constructional Steel Re-search vol 100 pp 211ndash228 2014

[6] L Han H Shan-Hu and F Liao ldquoPerformance and calcu-lations of concrete filled steel tubes (CFST) under axialtensionrdquo Journal of Constructional Steel Research vol 67no 11 pp 1699ndash1709 2011

[7] M A Bradford ldquoDesign strength of slender concrete filledrectangular steel tubesrdquo ACI Structural Journal vol 93 no 2pp 229ndash235 1996

[8] M D OrsquoShea and R Q Bridge ldquoDesign of thin-walledconcrete filled steel tubesrdquo Journal of Structural Engineer-ing vol 126 no 11 pp 1295ndash1303 2000

[9] B Uy ldquoLocal and postlocal buckling of fabricated steel andcomposite cross sectionsrdquo Journal of Structural Engineeringvol 127 no 6 pp 666ndash677 2001

[10] K K Choi and Y Xiao ldquoAnalytical studies of concrete-filledcircular steel tubes under axial compressionrdquo Journal ofStructural Engineering vol 136 no 5 pp 565ndash573 2010

[11] Z Ou B Chen K H Hsieh M W Halling and P J BarrldquoExperimental and analytical investigation of concrete filledsteel tubular columnsrdquo Journal of Structural Engineeringvol 137 no 6 pp 635ndash645 2011

[12] T Perea R T Leon J F Hajjar and M D Denavit ldquoFull-scale tests of slender concrete-filled tubes axial behaviorrdquoJournal of Structural Engineering vol 139 no 7 pp 1249ndash1262 2013

[13] L H Han ldquoFlexural behavior of concrete-filled steel tubesrdquoJournal of Constructional Steel Research vol 60 no 2pp 313ndash337 2004

[14] L H Han ldquoFurther study on the flexural behavior ofconcrete-filled steel tubesrdquo Journal of Constructional SteelResearch vol 62 no 6 pp 554ndash565 2006

[15] H Lu L H Han and X L Zhao ldquoAnalytical behavior ofcircular concrete-filled thin-walled steel tubes subjected tobendingrdquoin-Walled Structures vol 47 no 3 pp 346ndash3582009

[16] C W Roeder D E Lehman and E Bishop ldquoStrength andstiffness of circular concrete-filled tubesrdquo Journal of StructuralEngineering vol 136 no 12 pp 1545ndash1553 2010

[17] J Moon C W Roeder D E Lehman and H Lee ldquoAnalyticalmodeling of bending of circular concrete-filled steel tubesrdquoEngineering Structures vol 42 pp 349ndash361 2012

[18] L H Han G H Yao and Z Tao ldquoPerformance of concrete-filled thin-walled steel tubes under pure torsionrdquoin-WalledStructures vol 45 no 1 pp 24ndash36 2007

[19] J Nie Y Wang and J Fan ldquoExperimental study on seismicbehavior of concrete filled steel tube columns under puretorsion and compressionndashtorsion cyclic loadrdquo Journal ofConstructional Steel Research vol 79 no 12 pp 115ndash1262013

[20] Y Wang J Nie and J Fan ldquo+eoretical model and in-vestigation of concrete filled steel tube columns under axial

14 Advances in Materials Science and Engineering

forcendashtorsion combined actionrdquo in-Walled Structuresvol 69 no 1 pp 1ndash9 2013

[21] American Institute of Steel Construction AISCndashLRFD MetricLoad and Resistance Factor Design Specification for StructuralSteel Buildings AISC Chicago IL USA 1994

[22] Europe en Comite de Normalisation ENV 1994ndash1ndash1 Euro-code 4mdashDesign of Composite Steel and Concrete StructuresPart 11 General Rules and Rules for Buildings CEN BrusselsBelgium 1994

[23] Brazilian Society of Standard Codes NBR 8800 Design andConstructional Details of Steel Structures of Buildings Bra-zilian Society of Standard Codes Rio de Janeiro Brazil 1986

[24] Brazilian Society of Standard Codes NBR 8800 BrazilianStandard Code Review Design and Constructional Details ofSteel and Composite Structures of Buildings BSSC BeloHorizonte Brazil 2003

[25] National Standards of the Peoplersquos Republic of China GB50936 Technical Code for Concrete Filled Steel TubularStructures National Standards of the Peoplersquos Republic ofChina Beijing China 2014 in Chinese

[26] Q Liu D Wang R Huang et al ldquoStudy on failure mode ofinland river large water level dock under ship impactrdquo PortEngineering Technology vol 47 no 4 2010 in Chinese

[27] J Xu ldquoStructural design of overhead vertical wharf for inlandriver large water levelrdquo Water Transport Engineeringvol 2006 pp 62ndash67 2006 in Chinese

[28] China Association for Engineering Construction Standardi-zation CECS 2890 Specification for Design and Constructionof Concrete-Filled Steel Tubular Structures China Associationfor Engineering Construction Standardization BeijingChina 2012 in Chinese

Advances in Materials Science and Engineering 15

CorrosionInternational Journal of

Hindawiwwwhindawicom Volume 2018

Advances in

Materials Science and EngineeringHindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Journal of

Chemistry

Analytical ChemistryInternational Journal of

Hindawiwwwhindawicom Volume 2018

ScienticaHindawiwwwhindawicom Volume 2018

Polymer ScienceInternational Journal of

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Advances in Condensed Matter Physics

Hindawiwwwhindawicom Volume 2018

International Journal of

BiomaterialsHindawiwwwhindawicom

Journal ofEngineeringVolume 2018

Applied ChemistryJournal of

Hindawiwwwhindawicom Volume 2018

NanotechnologyHindawiwwwhindawicom Volume 2018

Journal of

Hindawiwwwhindawicom Volume 2018

High Energy PhysicsAdvances in

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom

The Scientific World Journal

Volume 2018

TribologyAdvances in

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

ChemistryAdvances in

Hindawiwwwhindawicom Volume 2018

Advances inPhysical Chemistry

Hindawiwwwhindawicom Volume 2018

BioMed Research InternationalMaterials

Journal of

Hindawiwwwhindawicom Volume 2018

Na

nom

ate

ria

ls

Hindawiwwwhindawicom Volume 2018

Journal ofNanomaterials

Submit your manuscripts atwwwhindawicom

loading given by MEdNEd and d is the external diameter ofthe column e plastic resistance to compression may thenbe calculated from the following expression in equations(2)ndash(5) e application of EC4 [22] is restricted to com-posite columns with steel yield stress and concrete cylinderstrength of less than 355 and 50MPa respectively efollowing presents the formulations of the AISC [21] EC4[22] NBR 8800 [23 24] and GB50396-2014 [25] standardcodes to determine the resistance capacity of axially loadedCFST columns And rs is the radius of gyration of the steelhollow section le is the length of the column Ec is themodulus of elasticity of the concrete and Es is the modulusof elasticity of the steel e formulations presented were

used to calculate the compressive strength of the axiallyloaded CFST columns investigated in the present study Inaddition the boundary conditions of the testing approachare upper if the pile is loading and lower if the pile is xed

In GB50396-2014 [25] θ means the hoop coecurrencient ofconcrete-lled steel tubular members θ αscffc αsc rep-resents the steel content of concrete-lled steel tubularmembers in the design of compressive strength of concrete-lled steel tube piles B and C are the inuence factors of thecross-sectional shape on the hoop eect and about circularcross section B 0176lowast f213 + 0974 Cminus0104fc144+ 0031 In AISC [21] the axial compression member isconsidered to be the overall stability of the member the

0 1000 2000 40003000Strain (με)

5000 6000 7000

Top loopCentral loopBottom loop

1000

1200

800

600

400

200

0

Load

(kN

)

(a)

0 1000 2000 40003000Strain (με)

5000 6000 7000

Top loopCentral loopBottom loop

50

60

40

30

20

10

0

Ave

rage

stre

ss (M

Pa)

(b)

Figure 15 Loop strain development of specimen RS-B-2 with steel casing (a) Relationship of strain development with load (b) Relationshipof strain development with average stress

0 200 400 800600 1000

Concrete

1200 1400 1600 1800Strain (με)

500

600

700

800

400

300

200

100

0

Load

(kN

)

(a)

0 200 400 800600 1000

Concrete

1200 1400 1600 1800Strain (με)

30

35

40

25

20

15

5

10

0

Ave

rage

stre

ss (M

Pa)

(b)

Figure 16 Axial compressive strain development of core concrete of specimen RS-B-2

Advances in Materials Science and Engineering 11

strength of the concrete is converted into the steel thenominal compressive strength fcr of the steel is obtained andthe bearing capacity of the concrete-lled steel tubularmember is calculated from fcr fys is the yield limit of steel fckmeans the compressive strength of concrete cylinder As isthe cross-sectional area of steel pipe Ac is the cross-sectionalarea of concrete and λc is the ratio of slenderness toslenderness In Eurocode 4 (EC4) [22] the relative slen-derness λ for the plane of bending being considered is givenby λ

NPLRkNcrradic

where NplRk is the characteristic valueof the plastic resistance to compression if instead ofthe design strengths the characteristic values are used andNcr is the elastic critical normal force for the relevantbuckling mode calculated with the eective exuralstiness (EI)c

However it should be stated that the maximum allowablevalue of diameter-thickness ratio (Dt) specied in AISC [21]is 031lowast Efy the ratio of diameter-thickness of circular-section concrete-lled steel tubular members specied inChinese specication [28] should be limited to the followingrange 20

235fy

radicleDtle 85

235fy

radic and Eurocode 4 (EC4)

[22] explicit limits the allowed Dt values in the Europeancontext to 90lowast 235fy e diameter-thickness ratio of thespecimens studied in this paper is very large exceeding theallowable range of the specications e paper attempts toestimate these specimens with large diameter-thickness ratioby using the above codes And the ultimate strength calcu-lation results of relevant specications are shown in Table 7Apparently it can be found that value of the ultimate load isgenerallymuch greater than the theoretical calculation results

25

25

20

20

Z1P1Z1P2

Load

(kN

) 15

15

10

10

5

50

0Vertical displacement (mm)

(a)

Z2P2Z2P1

25

30

20

Load

(kN

)

15

10

5

025 30 3520151050

Vertical displacement (mm)

(b)

Z3P2Z3P1

30

40

20

Load

(kN

)

10

025 30 352015

Vertical displacement (mm)1050

(c)

Figure 17 Relationship of vertical displacement and load of three depths of rock-socketed columns (a) Rock-socketed depth is 300mm (P1steel tube is 1mm P2 steel tube is 0mm) (b) Rock-socketed depth is 400mm (c) Rock-socketed depth is 500mm

12 Advances in Materials Science and Engineering

AISC [21] method

Em Es + 04EcAc

As

fmy fys + 085fckAc

As

fcr 0658λ2c( )fmy if λc le 15

fcr 0877λ2c

fmy if λc le 15

λc lcrcπ

fmy

Em( )

05

NplRd 085Asfcr

(1)

EC4 and NBR 8800 [23 24] methods

NplRd η2Asfy + Acfck 1 + η1tfy

Dfck( ) (2)

η1 η10η2 η20

(3)

η10 49minus 185 times λ + 17(λ)2 ge 0 (4)

η20 025(3 + 2λ)le 10 (5)

GB50396-2014 [25] method

N0 Ascfsc

fsc 1212 + Bθ + Cθ2( )fc

αsc As

Ac

θ αscf

fc

(6)

5 Conclusion

e present study is an attempt to study the behavior ofconcrete-lled steel tube columns subjected to axialcompression Based on the results of this study the fol-lowing conclusions can be drawn within the scope of thesetests

Table 7 e ultimate strength calculation results of relevant specications

Specimens Ultimate load (kN) NBR 8800 and EC4 (kN) AISC (kN) GB50396-2014 (kN)PL-2 406 412 419 429NS-A-2 830 493 479 560NS-B-2 885 566 535 603RN-2 560 430 416 465RS-A-2 895 493 479 596RS-B-2 1190 566 535 639PL-1 480 513 519 530NS-A-1 800 428 409 478RS-A-1 895 428 409 478RS-B-1 1125 452 474 498

35

40

45

30Load

(kN

)25

2030 35 40 45 50 55

n

P1P2

Figure 18 Relationship between n and load (n ratio of rock-socketed depth n hD)

Advances in Materials Science and Engineering 13

(1) +e reinforced CFST piles exhibit two differentfailure modes When the weld strength of the steelcasing is greater than the axial load limit of thecomposite member the failure mode is the bendingfailure caused by the local buckling deformationwhich is a ductile failure feature When the weldstrength of the steel casing is less than the axial loadlimit of the composite member the failure mode isthe open splitting of the steel casing weld under theexpansion stress of the concrete which is a brittlefailure feature

(2) +e bearing capacity of rock-socketed CFSTcolumnsis lower than that of rock-socketed columns withouta steel tube under the same conditions of a verticalload +e depth of the rock inlay is clearly affectingby the bearing capacity of the two rock-socketedcolumns and the greater the rock-socketed depththe greater the bearing capacity of the rock-socketedpiles In addition the overall sliding of the steel tubeand the core concrete of pile is small and the steeltube-concrete interface is basically in a bonding stateunder the vertical load

(3) A comparison of failure loads between the tests andthe design codes was presented+e results show thatthe provisions in EC4 [22] NBR 8800 [23 24] AISC[21] and GB50396-2014 [25]conservatively estimatethe ultimate capacities of the specimens and it can befound that value of the ultimate load is generallymuch greater than the theoretical calculation resultsSince the diameter-thickness ratio of the specimensstudied in this paper is very large exceeding theallowable range of the specifications the test resultsprovide a reference for design and performance ofthe new structure with large diameter-thicknessratio

Data Availability

+e figures and tables data used to support the findings ofthis study are included within the article

Conflicts of Interest

+e authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

+is study was financially supported by the National NaturalScience Foundation of China (nos 2011550031 and51709026) and the Western Project of China (nos2011660041 and 2011560076)

References

[1] S Jegadesh and S Jayalekshmi ldquoLoad-bearing capacity ofaxially loaded circular concrete-filled steel tubular columnsrdquoProceedings of the Institution of Civil Engineers Structures andBuildings vol 169 no 7 pp 508ndash523 2016

[2] N E Shanmugam and B Lakshmi ldquoState of the art report onsteelndashconcrete composite columnsrdquo Journal of ConstructionalResearch vol 57 no 10 pp 1041ndash1080 2001

[3] S De Nardin ldquoeoretical-experimental study high strengthconcrete-filled steel tubesrdquo MS thesis EESC-USP Sao Carlos-SP 1999 in Portuguese

[4] K Cederwall B Engstrom and M Grauers ldquoHigh-strengthconcrete used in composite columnsrdquo in Proceedings of High-Strength Concretendash2nd International Symposium pp 195ndash214Detroit MI USA 1990

[5] L Han W Li and R Bjorhovde ldquoDevelopments and ad-vanced applications of concrete-filled steel tubular (CFST)structures membersrdquo Journal of Constructional Steel Re-search vol 100 pp 211ndash228 2014

[6] L Han H Shan-Hu and F Liao ldquoPerformance and calcu-lations of concrete filled steel tubes (CFST) under axialtensionrdquo Journal of Constructional Steel Research vol 67no 11 pp 1699ndash1709 2011

[7] M A Bradford ldquoDesign strength of slender concrete filledrectangular steel tubesrdquo ACI Structural Journal vol 93 no 2pp 229ndash235 1996

[8] M D OrsquoShea and R Q Bridge ldquoDesign of thin-walledconcrete filled steel tubesrdquo Journal of Structural Engineer-ing vol 126 no 11 pp 1295ndash1303 2000

[9] B Uy ldquoLocal and postlocal buckling of fabricated steel andcomposite cross sectionsrdquo Journal of Structural Engineeringvol 127 no 6 pp 666ndash677 2001

[10] K K Choi and Y Xiao ldquoAnalytical studies of concrete-filledcircular steel tubes under axial compressionrdquo Journal ofStructural Engineering vol 136 no 5 pp 565ndash573 2010

[11] Z Ou B Chen K H Hsieh M W Halling and P J BarrldquoExperimental and analytical investigation of concrete filledsteel tubular columnsrdquo Journal of Structural Engineeringvol 137 no 6 pp 635ndash645 2011

[12] T Perea R T Leon J F Hajjar and M D Denavit ldquoFull-scale tests of slender concrete-filled tubes axial behaviorrdquoJournal of Structural Engineering vol 139 no 7 pp 1249ndash1262 2013

[13] L H Han ldquoFlexural behavior of concrete-filled steel tubesrdquoJournal of Constructional Steel Research vol 60 no 2pp 313ndash337 2004

[14] L H Han ldquoFurther study on the flexural behavior ofconcrete-filled steel tubesrdquo Journal of Constructional SteelResearch vol 62 no 6 pp 554ndash565 2006

[15] H Lu L H Han and X L Zhao ldquoAnalytical behavior ofcircular concrete-filled thin-walled steel tubes subjected tobendingrdquoin-Walled Structures vol 47 no 3 pp 346ndash3582009

[16] C W Roeder D E Lehman and E Bishop ldquoStrength andstiffness of circular concrete-filled tubesrdquo Journal of StructuralEngineering vol 136 no 12 pp 1545ndash1553 2010

[17] J Moon C W Roeder D E Lehman and H Lee ldquoAnalyticalmodeling of bending of circular concrete-filled steel tubesrdquoEngineering Structures vol 42 pp 349ndash361 2012

[18] L H Han G H Yao and Z Tao ldquoPerformance of concrete-filled thin-walled steel tubes under pure torsionrdquoin-WalledStructures vol 45 no 1 pp 24ndash36 2007

[19] J Nie Y Wang and J Fan ldquoExperimental study on seismicbehavior of concrete filled steel tube columns under puretorsion and compressionndashtorsion cyclic loadrdquo Journal ofConstructional Steel Research vol 79 no 12 pp 115ndash1262013

[20] Y Wang J Nie and J Fan ldquo+eoretical model and in-vestigation of concrete filled steel tube columns under axial

14 Advances in Materials Science and Engineering

forcendashtorsion combined actionrdquo in-Walled Structuresvol 69 no 1 pp 1ndash9 2013

[21] American Institute of Steel Construction AISCndashLRFD MetricLoad and Resistance Factor Design Specification for StructuralSteel Buildings AISC Chicago IL USA 1994

[22] Europe en Comite de Normalisation ENV 1994ndash1ndash1 Euro-code 4mdashDesign of Composite Steel and Concrete StructuresPart 11 General Rules and Rules for Buildings CEN BrusselsBelgium 1994

[23] Brazilian Society of Standard Codes NBR 8800 Design andConstructional Details of Steel Structures of Buildings Bra-zilian Society of Standard Codes Rio de Janeiro Brazil 1986

[24] Brazilian Society of Standard Codes NBR 8800 BrazilianStandard Code Review Design and Constructional Details ofSteel and Composite Structures of Buildings BSSC BeloHorizonte Brazil 2003

[25] National Standards of the Peoplersquos Republic of China GB50936 Technical Code for Concrete Filled Steel TubularStructures National Standards of the Peoplersquos Republic ofChina Beijing China 2014 in Chinese

[26] Q Liu D Wang R Huang et al ldquoStudy on failure mode ofinland river large water level dock under ship impactrdquo PortEngineering Technology vol 47 no 4 2010 in Chinese

[27] J Xu ldquoStructural design of overhead vertical wharf for inlandriver large water levelrdquo Water Transport Engineeringvol 2006 pp 62ndash67 2006 in Chinese

[28] China Association for Engineering Construction Standardi-zation CECS 2890 Specification for Design and Constructionof Concrete-Filled Steel Tubular Structures China Associationfor Engineering Construction Standardization BeijingChina 2012 in Chinese

Advances in Materials Science and Engineering 15

CorrosionInternational Journal of

Hindawiwwwhindawicom Volume 2018

Advances in

Materials Science and EngineeringHindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Journal of

Chemistry

Analytical ChemistryInternational Journal of

Hindawiwwwhindawicom Volume 2018

ScienticaHindawiwwwhindawicom Volume 2018

Polymer ScienceInternational Journal of

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Advances in Condensed Matter Physics

Hindawiwwwhindawicom Volume 2018

International Journal of

BiomaterialsHindawiwwwhindawicom

Journal ofEngineeringVolume 2018

Applied ChemistryJournal of

Hindawiwwwhindawicom Volume 2018

NanotechnologyHindawiwwwhindawicom Volume 2018

Journal of

Hindawiwwwhindawicom Volume 2018

High Energy PhysicsAdvances in

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom

The Scientific World Journal

Volume 2018

TribologyAdvances in

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

ChemistryAdvances in

Hindawiwwwhindawicom Volume 2018

Advances inPhysical Chemistry

Hindawiwwwhindawicom Volume 2018

BioMed Research InternationalMaterials

Journal of

Hindawiwwwhindawicom Volume 2018

Na

nom

ate

ria

ls

Hindawiwwwhindawicom Volume 2018

Journal ofNanomaterials

Submit your manuscripts atwwwhindawicom

strength of the concrete is converted into the steel thenominal compressive strength fcr of the steel is obtained andthe bearing capacity of the concrete-lled steel tubularmember is calculated from fcr fys is the yield limit of steel fckmeans the compressive strength of concrete cylinder As isthe cross-sectional area of steel pipe Ac is the cross-sectionalarea of concrete and λc is the ratio of slenderness toslenderness In Eurocode 4 (EC4) [22] the relative slen-derness λ for the plane of bending being considered is givenby λ

NPLRkNcrradic

where NplRk is the characteristic valueof the plastic resistance to compression if instead ofthe design strengths the characteristic values are used andNcr is the elastic critical normal force for the relevantbuckling mode calculated with the eective exuralstiness (EI)c

However it should be stated that the maximum allowablevalue of diameter-thickness ratio (Dt) specied in AISC [21]is 031lowast Efy the ratio of diameter-thickness of circular-section concrete-lled steel tubular members specied inChinese specication [28] should be limited to the followingrange 20

235fy

radicleDtle 85

235fy

radic and Eurocode 4 (EC4)

[22] explicit limits the allowed Dt values in the Europeancontext to 90lowast 235fy e diameter-thickness ratio of thespecimens studied in this paper is very large exceeding theallowable range of the specications e paper attempts toestimate these specimens with large diameter-thickness ratioby using the above codes And the ultimate strength calcu-lation results of relevant specications are shown in Table 7Apparently it can be found that value of the ultimate load isgenerallymuch greater than the theoretical calculation results

25

25

20

20

Z1P1Z1P2

Load

(kN

) 15

15

10

10

5

50

0Vertical displacement (mm)

(a)

Z2P2Z2P1

25

30

20

Load

(kN

)

15

10

5

025 30 3520151050

Vertical displacement (mm)

(b)

Z3P2Z3P1

30

40

20

Load

(kN

)

10

025 30 352015

Vertical displacement (mm)1050

(c)

Figure 17 Relationship of vertical displacement and load of three depths of rock-socketed columns (a) Rock-socketed depth is 300mm (P1steel tube is 1mm P2 steel tube is 0mm) (b) Rock-socketed depth is 400mm (c) Rock-socketed depth is 500mm

12 Advances in Materials Science and Engineering

AISC [21] method

Em Es + 04EcAc

As

fmy fys + 085fckAc

As

fcr 0658λ2c( )fmy if λc le 15

fcr 0877λ2c

fmy if λc le 15

λc lcrcπ

fmy

Em( )

05

NplRd 085Asfcr

(1)

EC4 and NBR 8800 [23 24] methods

NplRd η2Asfy + Acfck 1 + η1tfy

Dfck( ) (2)

η1 η10η2 η20

(3)

η10 49minus 185 times λ + 17(λ)2 ge 0 (4)

η20 025(3 + 2λ)le 10 (5)

GB50396-2014 [25] method

N0 Ascfsc

fsc 1212 + Bθ + Cθ2( )fc

αsc As

Ac

θ αscf

fc

(6)

5 Conclusion

e present study is an attempt to study the behavior ofconcrete-lled steel tube columns subjected to axialcompression Based on the results of this study the fol-lowing conclusions can be drawn within the scope of thesetests

Table 7 e ultimate strength calculation results of relevant specications

Specimens Ultimate load (kN) NBR 8800 and EC4 (kN) AISC (kN) GB50396-2014 (kN)PL-2 406 412 419 429NS-A-2 830 493 479 560NS-B-2 885 566 535 603RN-2 560 430 416 465RS-A-2 895 493 479 596RS-B-2 1190 566 535 639PL-1 480 513 519 530NS-A-1 800 428 409 478RS-A-1 895 428 409 478RS-B-1 1125 452 474 498

35

40

45

30Load

(kN

)25

2030 35 40 45 50 55

n

P1P2

Figure 18 Relationship between n and load (n ratio of rock-socketed depth n hD)

Advances in Materials Science and Engineering 13

(1) +e reinforced CFST piles exhibit two differentfailure modes When the weld strength of the steelcasing is greater than the axial load limit of thecomposite member the failure mode is the bendingfailure caused by the local buckling deformationwhich is a ductile failure feature When the weldstrength of the steel casing is less than the axial loadlimit of the composite member the failure mode isthe open splitting of the steel casing weld under theexpansion stress of the concrete which is a brittlefailure feature

(2) +e bearing capacity of rock-socketed CFSTcolumnsis lower than that of rock-socketed columns withouta steel tube under the same conditions of a verticalload +e depth of the rock inlay is clearly affectingby the bearing capacity of the two rock-socketedcolumns and the greater the rock-socketed depththe greater the bearing capacity of the rock-socketedpiles In addition the overall sliding of the steel tubeand the core concrete of pile is small and the steeltube-concrete interface is basically in a bonding stateunder the vertical load

(3) A comparison of failure loads between the tests andthe design codes was presented+e results show thatthe provisions in EC4 [22] NBR 8800 [23 24] AISC[21] and GB50396-2014 [25]conservatively estimatethe ultimate capacities of the specimens and it can befound that value of the ultimate load is generallymuch greater than the theoretical calculation resultsSince the diameter-thickness ratio of the specimensstudied in this paper is very large exceeding theallowable range of the specifications the test resultsprovide a reference for design and performance ofthe new structure with large diameter-thicknessratio

Data Availability

+e figures and tables data used to support the findings ofthis study are included within the article

Conflicts of Interest

+e authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

+is study was financially supported by the National NaturalScience Foundation of China (nos 2011550031 and51709026) and the Western Project of China (nos2011660041 and 2011560076)

References

[1] S Jegadesh and S Jayalekshmi ldquoLoad-bearing capacity ofaxially loaded circular concrete-filled steel tubular columnsrdquoProceedings of the Institution of Civil Engineers Structures andBuildings vol 169 no 7 pp 508ndash523 2016

[2] N E Shanmugam and B Lakshmi ldquoState of the art report onsteelndashconcrete composite columnsrdquo Journal of ConstructionalResearch vol 57 no 10 pp 1041ndash1080 2001

[3] S De Nardin ldquoeoretical-experimental study high strengthconcrete-filled steel tubesrdquo MS thesis EESC-USP Sao Carlos-SP 1999 in Portuguese

[4] K Cederwall B Engstrom and M Grauers ldquoHigh-strengthconcrete used in composite columnsrdquo in Proceedings of High-Strength Concretendash2nd International Symposium pp 195ndash214Detroit MI USA 1990

[5] L Han W Li and R Bjorhovde ldquoDevelopments and ad-vanced applications of concrete-filled steel tubular (CFST)structures membersrdquo Journal of Constructional Steel Re-search vol 100 pp 211ndash228 2014

[6] L Han H Shan-Hu and F Liao ldquoPerformance and calcu-lations of concrete filled steel tubes (CFST) under axialtensionrdquo Journal of Constructional Steel Research vol 67no 11 pp 1699ndash1709 2011

[7] M A Bradford ldquoDesign strength of slender concrete filledrectangular steel tubesrdquo ACI Structural Journal vol 93 no 2pp 229ndash235 1996

[8] M D OrsquoShea and R Q Bridge ldquoDesign of thin-walledconcrete filled steel tubesrdquo Journal of Structural Engineer-ing vol 126 no 11 pp 1295ndash1303 2000

[9] B Uy ldquoLocal and postlocal buckling of fabricated steel andcomposite cross sectionsrdquo Journal of Structural Engineeringvol 127 no 6 pp 666ndash677 2001

[10] K K Choi and Y Xiao ldquoAnalytical studies of concrete-filledcircular steel tubes under axial compressionrdquo Journal ofStructural Engineering vol 136 no 5 pp 565ndash573 2010

[11] Z Ou B Chen K H Hsieh M W Halling and P J BarrldquoExperimental and analytical investigation of concrete filledsteel tubular columnsrdquo Journal of Structural Engineeringvol 137 no 6 pp 635ndash645 2011

[12] T Perea R T Leon J F Hajjar and M D Denavit ldquoFull-scale tests of slender concrete-filled tubes axial behaviorrdquoJournal of Structural Engineering vol 139 no 7 pp 1249ndash1262 2013

[13] L H Han ldquoFlexural behavior of concrete-filled steel tubesrdquoJournal of Constructional Steel Research vol 60 no 2pp 313ndash337 2004

[14] L H Han ldquoFurther study on the flexural behavior ofconcrete-filled steel tubesrdquo Journal of Constructional SteelResearch vol 62 no 6 pp 554ndash565 2006

[15] H Lu L H Han and X L Zhao ldquoAnalytical behavior ofcircular concrete-filled thin-walled steel tubes subjected tobendingrdquoin-Walled Structures vol 47 no 3 pp 346ndash3582009

[16] C W Roeder D E Lehman and E Bishop ldquoStrength andstiffness of circular concrete-filled tubesrdquo Journal of StructuralEngineering vol 136 no 12 pp 1545ndash1553 2010

[17] J Moon C W Roeder D E Lehman and H Lee ldquoAnalyticalmodeling of bending of circular concrete-filled steel tubesrdquoEngineering Structures vol 42 pp 349ndash361 2012

[18] L H Han G H Yao and Z Tao ldquoPerformance of concrete-filled thin-walled steel tubes under pure torsionrdquoin-WalledStructures vol 45 no 1 pp 24ndash36 2007

[19] J Nie Y Wang and J Fan ldquoExperimental study on seismicbehavior of concrete filled steel tube columns under puretorsion and compressionndashtorsion cyclic loadrdquo Journal ofConstructional Steel Research vol 79 no 12 pp 115ndash1262013

[20] Y Wang J Nie and J Fan ldquo+eoretical model and in-vestigation of concrete filled steel tube columns under axial

14 Advances in Materials Science and Engineering

forcendashtorsion combined actionrdquo in-Walled Structuresvol 69 no 1 pp 1ndash9 2013

[21] American Institute of Steel Construction AISCndashLRFD MetricLoad and Resistance Factor Design Specification for StructuralSteel Buildings AISC Chicago IL USA 1994

[22] Europe en Comite de Normalisation ENV 1994ndash1ndash1 Euro-code 4mdashDesign of Composite Steel and Concrete StructuresPart 11 General Rules and Rules for Buildings CEN BrusselsBelgium 1994

[23] Brazilian Society of Standard Codes NBR 8800 Design andConstructional Details of Steel Structures of Buildings Bra-zilian Society of Standard Codes Rio de Janeiro Brazil 1986

[24] Brazilian Society of Standard Codes NBR 8800 BrazilianStandard Code Review Design and Constructional Details ofSteel and Composite Structures of Buildings BSSC BeloHorizonte Brazil 2003

[25] National Standards of the Peoplersquos Republic of China GB50936 Technical Code for Concrete Filled Steel TubularStructures National Standards of the Peoplersquos Republic ofChina Beijing China 2014 in Chinese

[26] Q Liu D Wang R Huang et al ldquoStudy on failure mode ofinland river large water level dock under ship impactrdquo PortEngineering Technology vol 47 no 4 2010 in Chinese

[27] J Xu ldquoStructural design of overhead vertical wharf for inlandriver large water levelrdquo Water Transport Engineeringvol 2006 pp 62ndash67 2006 in Chinese

[28] China Association for Engineering Construction Standardi-zation CECS 2890 Specification for Design and Constructionof Concrete-Filled Steel Tubular Structures China Associationfor Engineering Construction Standardization BeijingChina 2012 in Chinese

Advances in Materials Science and Engineering 15

CorrosionInternational Journal of

Hindawiwwwhindawicom Volume 2018

Advances in

Materials Science and EngineeringHindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Journal of

Chemistry

Analytical ChemistryInternational Journal of

Hindawiwwwhindawicom Volume 2018

ScienticaHindawiwwwhindawicom Volume 2018

Polymer ScienceInternational Journal of

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Advances in Condensed Matter Physics

Hindawiwwwhindawicom Volume 2018

International Journal of

BiomaterialsHindawiwwwhindawicom

Journal ofEngineeringVolume 2018

Applied ChemistryJournal of

Hindawiwwwhindawicom Volume 2018

NanotechnologyHindawiwwwhindawicom Volume 2018

Journal of

Hindawiwwwhindawicom Volume 2018

High Energy PhysicsAdvances in

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom

The Scientific World Journal

Volume 2018

TribologyAdvances in

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

ChemistryAdvances in

Hindawiwwwhindawicom Volume 2018

Advances inPhysical Chemistry

Hindawiwwwhindawicom Volume 2018

BioMed Research InternationalMaterials

Journal of

Hindawiwwwhindawicom Volume 2018

Na

nom

ate

ria

ls

Hindawiwwwhindawicom Volume 2018

Journal ofNanomaterials

Submit your manuscripts atwwwhindawicom

AISC [21] method

Em Es + 04EcAc

As

fmy fys + 085fckAc

As

fcr 0658λ2c( )fmy if λc le 15

fcr 0877λ2c

fmy if λc le 15

λc lcrcπ

fmy

Em( )

05

NplRd 085Asfcr

(1)

EC4 and NBR 8800 [23 24] methods

NplRd η2Asfy + Acfck 1 + η1tfy

Dfck( ) (2)

η1 η10η2 η20

(3)

η10 49minus 185 times λ + 17(λ)2 ge 0 (4)

η20 025(3 + 2λ)le 10 (5)

GB50396-2014 [25] method

N0 Ascfsc

fsc 1212 + Bθ + Cθ2( )fc

αsc As

Ac

θ αscf

fc

(6)

5 Conclusion

e present study is an attempt to study the behavior ofconcrete-lled steel tube columns subjected to axialcompression Based on the results of this study the fol-lowing conclusions can be drawn within the scope of thesetests

Table 7 e ultimate strength calculation results of relevant specications

Specimens Ultimate load (kN) NBR 8800 and EC4 (kN) AISC (kN) GB50396-2014 (kN)PL-2 406 412 419 429NS-A-2 830 493 479 560NS-B-2 885 566 535 603RN-2 560 430 416 465RS-A-2 895 493 479 596RS-B-2 1190 566 535 639PL-1 480 513 519 530NS-A-1 800 428 409 478RS-A-1 895 428 409 478RS-B-1 1125 452 474 498

35

40

45

30Load

(kN

)25

2030 35 40 45 50 55

n

P1P2

Figure 18 Relationship between n and load (n ratio of rock-socketed depth n hD)

Advances in Materials Science and Engineering 13

(1) +e reinforced CFST piles exhibit two differentfailure modes When the weld strength of the steelcasing is greater than the axial load limit of thecomposite member the failure mode is the bendingfailure caused by the local buckling deformationwhich is a ductile failure feature When the weldstrength of the steel casing is less than the axial loadlimit of the composite member the failure mode isthe open splitting of the steel casing weld under theexpansion stress of the concrete which is a brittlefailure feature

(2) +e bearing capacity of rock-socketed CFSTcolumnsis lower than that of rock-socketed columns withouta steel tube under the same conditions of a verticalload +e depth of the rock inlay is clearly affectingby the bearing capacity of the two rock-socketedcolumns and the greater the rock-socketed depththe greater the bearing capacity of the rock-socketedpiles In addition the overall sliding of the steel tubeand the core concrete of pile is small and the steeltube-concrete interface is basically in a bonding stateunder the vertical load

(3) A comparison of failure loads between the tests andthe design codes was presented+e results show thatthe provisions in EC4 [22] NBR 8800 [23 24] AISC[21] and GB50396-2014 [25]conservatively estimatethe ultimate capacities of the specimens and it can befound that value of the ultimate load is generallymuch greater than the theoretical calculation resultsSince the diameter-thickness ratio of the specimensstudied in this paper is very large exceeding theallowable range of the specifications the test resultsprovide a reference for design and performance ofthe new structure with large diameter-thicknessratio

Data Availability

+e figures and tables data used to support the findings ofthis study are included within the article

Conflicts of Interest

+e authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

+is study was financially supported by the National NaturalScience Foundation of China (nos 2011550031 and51709026) and the Western Project of China (nos2011660041 and 2011560076)

References

[1] S Jegadesh and S Jayalekshmi ldquoLoad-bearing capacity ofaxially loaded circular concrete-filled steel tubular columnsrdquoProceedings of the Institution of Civil Engineers Structures andBuildings vol 169 no 7 pp 508ndash523 2016

[2] N E Shanmugam and B Lakshmi ldquoState of the art report onsteelndashconcrete composite columnsrdquo Journal of ConstructionalResearch vol 57 no 10 pp 1041ndash1080 2001

[3] S De Nardin ldquoeoretical-experimental study high strengthconcrete-filled steel tubesrdquo MS thesis EESC-USP Sao Carlos-SP 1999 in Portuguese

[4] K Cederwall B Engstrom and M Grauers ldquoHigh-strengthconcrete used in composite columnsrdquo in Proceedings of High-Strength Concretendash2nd International Symposium pp 195ndash214Detroit MI USA 1990

[5] L Han W Li and R Bjorhovde ldquoDevelopments and ad-vanced applications of concrete-filled steel tubular (CFST)structures membersrdquo Journal of Constructional Steel Re-search vol 100 pp 211ndash228 2014

[6] L Han H Shan-Hu and F Liao ldquoPerformance and calcu-lations of concrete filled steel tubes (CFST) under axialtensionrdquo Journal of Constructional Steel Research vol 67no 11 pp 1699ndash1709 2011

[7] M A Bradford ldquoDesign strength of slender concrete filledrectangular steel tubesrdquo ACI Structural Journal vol 93 no 2pp 229ndash235 1996

[8] M D OrsquoShea and R Q Bridge ldquoDesign of thin-walledconcrete filled steel tubesrdquo Journal of Structural Engineer-ing vol 126 no 11 pp 1295ndash1303 2000

[9] B Uy ldquoLocal and postlocal buckling of fabricated steel andcomposite cross sectionsrdquo Journal of Structural Engineeringvol 127 no 6 pp 666ndash677 2001

[10] K K Choi and Y Xiao ldquoAnalytical studies of concrete-filledcircular steel tubes under axial compressionrdquo Journal ofStructural Engineering vol 136 no 5 pp 565ndash573 2010

[11] Z Ou B Chen K H Hsieh M W Halling and P J BarrldquoExperimental and analytical investigation of concrete filledsteel tubular columnsrdquo Journal of Structural Engineeringvol 137 no 6 pp 635ndash645 2011

[12] T Perea R T Leon J F Hajjar and M D Denavit ldquoFull-scale tests of slender concrete-filled tubes axial behaviorrdquoJournal of Structural Engineering vol 139 no 7 pp 1249ndash1262 2013

[13] L H Han ldquoFlexural behavior of concrete-filled steel tubesrdquoJournal of Constructional Steel Research vol 60 no 2pp 313ndash337 2004

[14] L H Han ldquoFurther study on the flexural behavior ofconcrete-filled steel tubesrdquo Journal of Constructional SteelResearch vol 62 no 6 pp 554ndash565 2006

[15] H Lu L H Han and X L Zhao ldquoAnalytical behavior ofcircular concrete-filled thin-walled steel tubes subjected tobendingrdquoin-Walled Structures vol 47 no 3 pp 346ndash3582009

[16] C W Roeder D E Lehman and E Bishop ldquoStrength andstiffness of circular concrete-filled tubesrdquo Journal of StructuralEngineering vol 136 no 12 pp 1545ndash1553 2010

[17] J Moon C W Roeder D E Lehman and H Lee ldquoAnalyticalmodeling of bending of circular concrete-filled steel tubesrdquoEngineering Structures vol 42 pp 349ndash361 2012

[18] L H Han G H Yao and Z Tao ldquoPerformance of concrete-filled thin-walled steel tubes under pure torsionrdquoin-WalledStructures vol 45 no 1 pp 24ndash36 2007

[19] J Nie Y Wang and J Fan ldquoExperimental study on seismicbehavior of concrete filled steel tube columns under puretorsion and compressionndashtorsion cyclic loadrdquo Journal ofConstructional Steel Research vol 79 no 12 pp 115ndash1262013

[20] Y Wang J Nie and J Fan ldquo+eoretical model and in-vestigation of concrete filled steel tube columns under axial

14 Advances in Materials Science and Engineering

forcendashtorsion combined actionrdquo in-Walled Structuresvol 69 no 1 pp 1ndash9 2013

[21] American Institute of Steel Construction AISCndashLRFD MetricLoad and Resistance Factor Design Specification for StructuralSteel Buildings AISC Chicago IL USA 1994

[22] Europe en Comite de Normalisation ENV 1994ndash1ndash1 Euro-code 4mdashDesign of Composite Steel and Concrete StructuresPart 11 General Rules and Rules for Buildings CEN BrusselsBelgium 1994

[23] Brazilian Society of Standard Codes NBR 8800 Design andConstructional Details of Steel Structures of Buildings Bra-zilian Society of Standard Codes Rio de Janeiro Brazil 1986

[24] Brazilian Society of Standard Codes NBR 8800 BrazilianStandard Code Review Design and Constructional Details ofSteel and Composite Structures of Buildings BSSC BeloHorizonte Brazil 2003

[25] National Standards of the Peoplersquos Republic of China GB50936 Technical Code for Concrete Filled Steel TubularStructures National Standards of the Peoplersquos Republic ofChina Beijing China 2014 in Chinese

[26] Q Liu D Wang R Huang et al ldquoStudy on failure mode ofinland river large water level dock under ship impactrdquo PortEngineering Technology vol 47 no 4 2010 in Chinese

[27] J Xu ldquoStructural design of overhead vertical wharf for inlandriver large water levelrdquo Water Transport Engineeringvol 2006 pp 62ndash67 2006 in Chinese

[28] China Association for Engineering Construction Standardi-zation CECS 2890 Specification for Design and Constructionof Concrete-Filled Steel Tubular Structures China Associationfor Engineering Construction Standardization BeijingChina 2012 in Chinese

Advances in Materials Science and Engineering 15

CorrosionInternational Journal of

Hindawiwwwhindawicom Volume 2018

Advances in

Materials Science and EngineeringHindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Journal of

Chemistry

Analytical ChemistryInternational Journal of

Hindawiwwwhindawicom Volume 2018

ScienticaHindawiwwwhindawicom Volume 2018

Polymer ScienceInternational Journal of

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Advances in Condensed Matter Physics

Hindawiwwwhindawicom Volume 2018

International Journal of

BiomaterialsHindawiwwwhindawicom

Journal ofEngineeringVolume 2018

Applied ChemistryJournal of

Hindawiwwwhindawicom Volume 2018

NanotechnologyHindawiwwwhindawicom Volume 2018

Journal of

Hindawiwwwhindawicom Volume 2018

High Energy PhysicsAdvances in

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom

The Scientific World Journal

Volume 2018

TribologyAdvances in

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

ChemistryAdvances in

Hindawiwwwhindawicom Volume 2018

Advances inPhysical Chemistry

Hindawiwwwhindawicom Volume 2018

BioMed Research InternationalMaterials

Journal of

Hindawiwwwhindawicom Volume 2018

Na

nom

ate

ria

ls

Hindawiwwwhindawicom Volume 2018

Journal ofNanomaterials

Submit your manuscripts atwwwhindawicom

(1) +e reinforced CFST piles exhibit two differentfailure modes When the weld strength of the steelcasing is greater than the axial load limit of thecomposite member the failure mode is the bendingfailure caused by the local buckling deformationwhich is a ductile failure feature When the weldstrength of the steel casing is less than the axial loadlimit of the composite member the failure mode isthe open splitting of the steel casing weld under theexpansion stress of the concrete which is a brittlefailure feature

(2) +e bearing capacity of rock-socketed CFSTcolumnsis lower than that of rock-socketed columns withouta steel tube under the same conditions of a verticalload +e depth of the rock inlay is clearly affectingby the bearing capacity of the two rock-socketedcolumns and the greater the rock-socketed depththe greater the bearing capacity of the rock-socketedpiles In addition the overall sliding of the steel tubeand the core concrete of pile is small and the steeltube-concrete interface is basically in a bonding stateunder the vertical load

(3) A comparison of failure loads between the tests andthe design codes was presented+e results show thatthe provisions in EC4 [22] NBR 8800 [23 24] AISC[21] and GB50396-2014 [25]conservatively estimatethe ultimate capacities of the specimens and it can befound that value of the ultimate load is generallymuch greater than the theoretical calculation resultsSince the diameter-thickness ratio of the specimensstudied in this paper is very large exceeding theallowable range of the specifications the test resultsprovide a reference for design and performance ofthe new structure with large diameter-thicknessratio

Data Availability

+e figures and tables data used to support the findings ofthis study are included within the article

Conflicts of Interest

+e authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

+is study was financially supported by the National NaturalScience Foundation of China (nos 2011550031 and51709026) and the Western Project of China (nos2011660041 and 2011560076)

References

[1] S Jegadesh and S Jayalekshmi ldquoLoad-bearing capacity ofaxially loaded circular concrete-filled steel tubular columnsrdquoProceedings of the Institution of Civil Engineers Structures andBuildings vol 169 no 7 pp 508ndash523 2016

[2] N E Shanmugam and B Lakshmi ldquoState of the art report onsteelndashconcrete composite columnsrdquo Journal of ConstructionalResearch vol 57 no 10 pp 1041ndash1080 2001

[3] S De Nardin ldquoeoretical-experimental study high strengthconcrete-filled steel tubesrdquo MS thesis EESC-USP Sao Carlos-SP 1999 in Portuguese

[4] K Cederwall B Engstrom and M Grauers ldquoHigh-strengthconcrete used in composite columnsrdquo in Proceedings of High-Strength Concretendash2nd International Symposium pp 195ndash214Detroit MI USA 1990

[5] L Han W Li and R Bjorhovde ldquoDevelopments and ad-vanced applications of concrete-filled steel tubular (CFST)structures membersrdquo Journal of Constructional Steel Re-search vol 100 pp 211ndash228 2014

[6] L Han H Shan-Hu and F Liao ldquoPerformance and calcu-lations of concrete filled steel tubes (CFST) under axialtensionrdquo Journal of Constructional Steel Research vol 67no 11 pp 1699ndash1709 2011

[7] M A Bradford ldquoDesign strength of slender concrete filledrectangular steel tubesrdquo ACI Structural Journal vol 93 no 2pp 229ndash235 1996

[8] M D OrsquoShea and R Q Bridge ldquoDesign of thin-walledconcrete filled steel tubesrdquo Journal of Structural Engineer-ing vol 126 no 11 pp 1295ndash1303 2000

[9] B Uy ldquoLocal and postlocal buckling of fabricated steel andcomposite cross sectionsrdquo Journal of Structural Engineeringvol 127 no 6 pp 666ndash677 2001

[10] K K Choi and Y Xiao ldquoAnalytical studies of concrete-filledcircular steel tubes under axial compressionrdquo Journal ofStructural Engineering vol 136 no 5 pp 565ndash573 2010

[11] Z Ou B Chen K H Hsieh M W Halling and P J BarrldquoExperimental and analytical investigation of concrete filledsteel tubular columnsrdquo Journal of Structural Engineeringvol 137 no 6 pp 635ndash645 2011

[12] T Perea R T Leon J F Hajjar and M D Denavit ldquoFull-scale tests of slender concrete-filled tubes axial behaviorrdquoJournal of Structural Engineering vol 139 no 7 pp 1249ndash1262 2013

[13] L H Han ldquoFlexural behavior of concrete-filled steel tubesrdquoJournal of Constructional Steel Research vol 60 no 2pp 313ndash337 2004

[14] L H Han ldquoFurther study on the flexural behavior ofconcrete-filled steel tubesrdquo Journal of Constructional SteelResearch vol 62 no 6 pp 554ndash565 2006

[15] H Lu L H Han and X L Zhao ldquoAnalytical behavior ofcircular concrete-filled thin-walled steel tubes subjected tobendingrdquoin-Walled Structures vol 47 no 3 pp 346ndash3582009

[16] C W Roeder D E Lehman and E Bishop ldquoStrength andstiffness of circular concrete-filled tubesrdquo Journal of StructuralEngineering vol 136 no 12 pp 1545ndash1553 2010

[17] J Moon C W Roeder D E Lehman and H Lee ldquoAnalyticalmodeling of bending of circular concrete-filled steel tubesrdquoEngineering Structures vol 42 pp 349ndash361 2012

[18] L H Han G H Yao and Z Tao ldquoPerformance of concrete-filled thin-walled steel tubes under pure torsionrdquoin-WalledStructures vol 45 no 1 pp 24ndash36 2007

[19] J Nie Y Wang and J Fan ldquoExperimental study on seismicbehavior of concrete filled steel tube columns under puretorsion and compressionndashtorsion cyclic loadrdquo Journal ofConstructional Steel Research vol 79 no 12 pp 115ndash1262013

[20] Y Wang J Nie and J Fan ldquo+eoretical model and in-vestigation of concrete filled steel tube columns under axial

14 Advances in Materials Science and Engineering

forcendashtorsion combined actionrdquo in-Walled Structuresvol 69 no 1 pp 1ndash9 2013

[21] American Institute of Steel Construction AISCndashLRFD MetricLoad and Resistance Factor Design Specification for StructuralSteel Buildings AISC Chicago IL USA 1994

[22] Europe en Comite de Normalisation ENV 1994ndash1ndash1 Euro-code 4mdashDesign of Composite Steel and Concrete StructuresPart 11 General Rules and Rules for Buildings CEN BrusselsBelgium 1994

[23] Brazilian Society of Standard Codes NBR 8800 Design andConstructional Details of Steel Structures of Buildings Bra-zilian Society of Standard Codes Rio de Janeiro Brazil 1986

[24] Brazilian Society of Standard Codes NBR 8800 BrazilianStandard Code Review Design and Constructional Details ofSteel and Composite Structures of Buildings BSSC BeloHorizonte Brazil 2003

[25] National Standards of the Peoplersquos Republic of China GB50936 Technical Code for Concrete Filled Steel TubularStructures National Standards of the Peoplersquos Republic ofChina Beijing China 2014 in Chinese

[26] Q Liu D Wang R Huang et al ldquoStudy on failure mode ofinland river large water level dock under ship impactrdquo PortEngineering Technology vol 47 no 4 2010 in Chinese

[27] J Xu ldquoStructural design of overhead vertical wharf for inlandriver large water levelrdquo Water Transport Engineeringvol 2006 pp 62ndash67 2006 in Chinese

[28] China Association for Engineering Construction Standardi-zation CECS 2890 Specification for Design and Constructionof Concrete-Filled Steel Tubular Structures China Associationfor Engineering Construction Standardization BeijingChina 2012 in Chinese

Advances in Materials Science and Engineering 15

CorrosionInternational Journal of

Hindawiwwwhindawicom Volume 2018

Advances in

Materials Science and EngineeringHindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Journal of

Chemistry

Analytical ChemistryInternational Journal of

Hindawiwwwhindawicom Volume 2018

ScienticaHindawiwwwhindawicom Volume 2018

Polymer ScienceInternational Journal of

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Advances in Condensed Matter Physics

Hindawiwwwhindawicom Volume 2018

International Journal of

BiomaterialsHindawiwwwhindawicom

Journal ofEngineeringVolume 2018

Applied ChemistryJournal of

Hindawiwwwhindawicom Volume 2018

NanotechnologyHindawiwwwhindawicom Volume 2018

Journal of

Hindawiwwwhindawicom Volume 2018

High Energy PhysicsAdvances in

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom

The Scientific World Journal

Volume 2018

TribologyAdvances in

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

ChemistryAdvances in

Hindawiwwwhindawicom Volume 2018

Advances inPhysical Chemistry

Hindawiwwwhindawicom Volume 2018

BioMed Research InternationalMaterials

Journal of

Hindawiwwwhindawicom Volume 2018

Na

nom

ate

ria

ls

Hindawiwwwhindawicom Volume 2018

Journal ofNanomaterials

Submit your manuscripts atwwwhindawicom

forcendashtorsion combined actionrdquo in-Walled Structuresvol 69 no 1 pp 1ndash9 2013

[21] American Institute of Steel Construction AISCndashLRFD MetricLoad and Resistance Factor Design Specification for StructuralSteel Buildings AISC Chicago IL USA 1994

[22] Europe en Comite de Normalisation ENV 1994ndash1ndash1 Euro-code 4mdashDesign of Composite Steel and Concrete StructuresPart 11 General Rules and Rules for Buildings CEN BrusselsBelgium 1994

[23] Brazilian Society of Standard Codes NBR 8800 Design andConstructional Details of Steel Structures of Buildings Bra-zilian Society of Standard Codes Rio de Janeiro Brazil 1986

[24] Brazilian Society of Standard Codes NBR 8800 BrazilianStandard Code Review Design and Constructional Details ofSteel and Composite Structures of Buildings BSSC BeloHorizonte Brazil 2003

[25] National Standards of the Peoplersquos Republic of China GB50936 Technical Code for Concrete Filled Steel TubularStructures National Standards of the Peoplersquos Republic ofChina Beijing China 2014 in Chinese

[26] Q Liu D Wang R Huang et al ldquoStudy on failure mode ofinland river large water level dock under ship impactrdquo PortEngineering Technology vol 47 no 4 2010 in Chinese

[27] J Xu ldquoStructural design of overhead vertical wharf for inlandriver large water levelrdquo Water Transport Engineeringvol 2006 pp 62ndash67 2006 in Chinese

[28] China Association for Engineering Construction Standardi-zation CECS 2890 Specification for Design and Constructionof Concrete-Filled Steel Tubular Structures China Associationfor Engineering Construction Standardization BeijingChina 2012 in Chinese

Advances in Materials Science and Engineering 15

CorrosionInternational Journal of

Hindawiwwwhindawicom Volume 2018

Advances in

Materials Science and EngineeringHindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Journal of

Chemistry

Analytical ChemistryInternational Journal of

Hindawiwwwhindawicom Volume 2018

ScienticaHindawiwwwhindawicom Volume 2018

Polymer ScienceInternational Journal of

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Advances in Condensed Matter Physics

Hindawiwwwhindawicom Volume 2018

International Journal of

BiomaterialsHindawiwwwhindawicom

Journal ofEngineeringVolume 2018

Applied ChemistryJournal of

Hindawiwwwhindawicom Volume 2018

NanotechnologyHindawiwwwhindawicom Volume 2018

Journal of

Hindawiwwwhindawicom Volume 2018

High Energy PhysicsAdvances in

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom

The Scientific World Journal

Volume 2018

TribologyAdvances in

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

ChemistryAdvances in

Hindawiwwwhindawicom Volume 2018

Advances inPhysical Chemistry

Hindawiwwwhindawicom Volume 2018

BioMed Research InternationalMaterials

Journal of

Hindawiwwwhindawicom Volume 2018

Na

nom

ate

ria

ls

Hindawiwwwhindawicom Volume 2018

Journal ofNanomaterials

Submit your manuscripts atwwwhindawicom

CorrosionInternational Journal of

Hindawiwwwhindawicom Volume 2018

Advances in

Materials Science and EngineeringHindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Journal of

Chemistry

Analytical ChemistryInternational Journal of

Hindawiwwwhindawicom Volume 2018

ScienticaHindawiwwwhindawicom Volume 2018

Polymer ScienceInternational Journal of

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Advances in Condensed Matter Physics

Hindawiwwwhindawicom Volume 2018

International Journal of

BiomaterialsHindawiwwwhindawicom

Journal ofEngineeringVolume 2018

Applied ChemistryJournal of

Hindawiwwwhindawicom Volume 2018

NanotechnologyHindawiwwwhindawicom Volume 2018

Journal of

Hindawiwwwhindawicom Volume 2018

High Energy PhysicsAdvances in

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom

The Scientific World Journal

Volume 2018

TribologyAdvances in

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

ChemistryAdvances in

Hindawiwwwhindawicom Volume 2018

Advances inPhysical Chemistry

Hindawiwwwhindawicom Volume 2018

BioMed Research InternationalMaterials

Journal of

Hindawiwwwhindawicom Volume 2018

Na

nom

ate

ria

ls

Hindawiwwwhindawicom Volume 2018

Journal ofNanomaterials

Submit your manuscripts atwwwhindawicom