Materials and Design 54 (2014) 686–693

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Materials and Design

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Technical Report

Behaviour of hybrid fibre reinforced concrete beam–column joints underreverse cyclic loads

0261-3069/$ - see front matter � 2013 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.matdes.2013.08.076

⇑ Corresponding author. Tel.: +91 0495 2286204.E-mail addresses: ganesan@nitc.ac.in (N. Ganesan), indira@nitc.ac.in (P.V.

Indira), sabeenahari@gmail.com (M.V. Sabeena).

N. Ganesan ⇑, P.V. Indira, M.V. SabeenaDepartment of Civil Engineering, National Institute of Technology Calicut, Kerala State 673601, India

a r t i c l e i n f o

Article history:Received 30 May 2013Accepted 21 August 2013Available online 30 August 2013

a b s t r a c t

An experimental investigation was carried out to study the effect of hybrid fibres on the strength andbehaviour of High performance concrete beam column joints subjected to reverse cyclic loads. A totalof 12 reinforced concrete beams column joints were cast and tested in the present investigation. Highperformance concrete of M60 grade was designed using the modified ACI method suggested by Aïtcin.Crimped steel fibres and polypropylene fibres were used in hybrid form. The main variables consideredwere the volume fraction of (i) crimped steel fibres viz. 0.5% (39.25 kg/m3) and 1.0% (78.5 kg/m3) and (ii)polypropylene fibres viz. 0.1% (0.9 kg/m3), 0.15% (1.35 kg/m3), and 0.2% (1.8 kg/m3). Addition of fibres inhybrid form improved many of the engineering properties such as the first crack load, ultimate load andductility factor of the composite. The combination of 1% (78.5 kg/m3) volume fraction of steel fibres and0.15% (1.35 kg/m3) volume fraction of polypropylene fibres gave better performance with respect toenergy dissipation capacity and stiffness degradation than the other combinations.

� 2013 Elsevier Ltd. All rights reserved.

1. Introduction

Beam column joints are the critical components of a reinforcedconcrete moment resisting frame, especially when the frame issubjected to seismic loading. Under large seismic forces, thebeam–column connections must be capable of carrying shearforces which are accompanied by large deformations. Therefore,for providing adequate ductility of beam–column joints the useof closely spaced hoops as transverse reinforcement was recom-mended in ACI-ASCE Committee 352 [1] and IS 13920 [2]. Thisleads to the congestion of reinforcement and difficulties in placingand consolidating the concrete in the joint regions. These problemshave led to considerable research for developing new methods toimprove the structural performance under seismic loading andone of the major achievements in this area is the use of Fibre Rein-forced Concrete (FRC). Fibres, if randomly dispersed throughoutthe concrete matrix, provide better distribution of both internaland external stresses due to the formation of a three dimensionalreinforcing network [3]. Addition of fibres into concrete have beeneffective in improving structural performance under gravity loads,as well as in increasing shear strength, ductility, energy dissipa-tion, and damage tolerance in members subjected to reverse cyclicloading [4,5]. One of the possible alternative solutions for reducingthe congestion of transverse reinforcement in beam column jointsis the use of steel fibre reinforced concrete in the joints [6,7]. The

characteristics of fibre reinforced concrete depend upon the prop-erties of fibres and volume fraction and each type of fibre can beeffective with regard to some specific function [8]. The mostimportant function of fibres in concrete is to bridge across thecracks and delay the propagation of cracks which provides post-cracking ductility. FRC used in practice usually contain only onetype of fibre. However, it is known that failure in concrete is a grad-ual, multi-scale process. Under an applied load, pre-existing microcracks in concrete grow and join together to form macro cracks. Amacro crack propagates at a stable rate until it attains conditions ofunstable propagation and cause a sudden failure. The gradual andmulti-scale nature of fracture in concrete implies that a given fibrecan provide reinforcement only at one level and within a limitedrange of strains [9]. Attempts have been made in the past to com-bine different types of fibres and addition of the same to cementi-tious composites in order to improve the cracking performance inconcrete at different levels [10,11]. Small and soft fibres controlinitiation and propagation of micro cracks and the large and strongfibres control macro cracks. Such hybrid fibre reinforced compositecan also offer more attractive engineering properties because thepresence of one type of fibre effectively utilizes the properties ofthe other fibre [12,13]. Investigations with different types of hybridfibres also indicate enhancement of durability when hybrid fibresare added to concrete [14]. Sustainability and durability are inter-related and they go together. Sustainability also relates to the lifeof the structure which in turn depends on concrete durability.The lifetime of the structure has a direct impact on sustainability.Enhancing the long term durability is one of the best solutions toimprove sustainability [15]. Modern concretes such as fibrous

N. Ganesan et al. / Materials and Design 54 (2014) 686–693 687

concrete, high performance concrete etc. not only enhance theproperties of concrete but also increase the life of structures builtwith them.

Improvement of strength and durability enhances the servicelife of structure which leads to reduction in the utilization of nat-ural resources such as lime stone (for the production of cement)and fine and coarse aggregates (for the production of concrete).Hence this proves beneficial to the conservation of natural re-sources to a great extent. Hence if one can achieve high durabilitythen automatically sustainability is attained.

Besides the above, the effect of presence of slabs on the behav-iour of joints has also been studied by many researchers. Ductilityof slab column joints depends upon the factors such as confiningeffect offered by the surrounding slab, load intensity on slab, slabreinforcement ratio and column and slab concrete strength[16,17]. The punching shear failure occurs in flat slabs due to highstress concentration in the slab-column connections. The use ofsteel fibre reinforcement improves the punching shear resistanceand controls the cracking of slab column connections [18]. Studieshave also been carried out on fibre reinforced high strength con-crete and it was reported that the addition of steel fibres to highstrength concrete makes it an effective high performance compos-ite and the post-cracking load mainly depends on the fibre content[18,19].

Large number of investigations are available on high strengthconcrete (HSC) [16,17], fibre reinforced HSC [18–20], high perfor-mance concrete(HPC) [21] and fibre reinforced HPC [6,22]. How-ever research on the effect of combination of different type offibres such as hybrid fibres on the strength and behaviour of HPCare limited. ACI [23] defines high performance concrete (HPC) asthe concrete meeting special combinations of performance anduniformity requirements that cannot always be achieved routinelywhen using conventional constituents and normal mixing, placingand curing practices. A high performance concrete is a concrete inwhich certain characteristics are developed for a particular appli-cation and environment. Examples of characteristics that may beconsidered critical for an application are ease of placement, com-paction without segregation, early age strength, long-termmechanical properties, permeability, density, heat of hydration,toughness, volume stability and long life in severe environments[23].

In general, when fibres are added to concrete, tensile strain inthe neighbourhood of fibres improves significantly. HPC has a verydense microstructure since it contains supplementary cementi-tious materials like fly ash and silica fume [21]. Hence in HPC, ten-sile strain carrying capacity would be much higher than that ofconventional concrete and this in turn will improve the crackingbehaviour, ductility and energy absorption capacity of the compos-ite. Considering this, an attempt was made to study the effect ofhigh performance concrete containing high modulus metallic fi-bres and low modulus synthetic fibres in combination with con-ventional reinforcement bars, to enhance the seismicperformance of the beam–column joints. This study focuses onthe hybrid fibre reinforced system containing crimped steel fibresand micro polypropylene fibres. Crimped steel fibres have undula-tions along the fibre length which provide mechanical anchorage ofthe fibres into the concrete, enhancing post first crack strength [8].Polypropylene fibres are effective in controlling the crack initiationat micro level [10].

2. Research significance

Ductile detailing for reinforced concrete framed structures isconsidered to be difficult because of the congestion of the trans-verse reinforcement and the problems in placing and compacting

of concrete in the beam–column joint regions. This study investi-gates the effect of hybrid fibres on the strength and behaviour ofexterior HPC beam column joints. The tests on external beam–col-umn joints showed the possibility of achieving highly ductilebehaviour by using HPC containing hybrid steel-polypropylene fi-bres. Also the use of hybrid fibres in the beam column joint willlead to reduction in the transverse reinforcement and hence thecongestion of steel reinforcement could be prevented in the joint.

3. Experimental programme

3.1. Materials used

Ordinary Portland Cement of (53 grade) conforming toIS:12269-1987 (reaffirmed 2004) [24], river sand passing through4.75 mm IS sieve conforming to grading zone II of IS: 383-1970(reaffirmed 2002) [25] with fineness modulus 2.46 and specificgravity 2.54 and crushed stone with a maximum size 12 mm withspecific gravity 2.77 were used for this investigation. Class F fly ashfrom Neyveli Lignite Corporation and Silica fume supplied by Elk-em Micro Silica were used as mineral admixtures. A naphthalenebased superplasticizer was used to obtain the required workability.Crimped steel fibres and polypropylene fibres used in this studyare shown in Fig. 1 and their properties are given in Table 1.

3.2. Mix proportions for HPC

ACI 211.1-91 [26] guidelines modified by Aïtcin [27] was fol-lowed for designing M60 grade HPC mix. Part of cement was re-placed by micro fillers such as flyash and silica fume. Addition offibres reduced the workability of HPC and hence the dosage ofsuperplasticizer was adjusted to maintain the workability. The de-tails of mix proportions are given in Table 2.

3.3. Details of specimens

The experimental programme consisted of casting and testing12 numbers of exterior beam column joints under reverse cyclicloading. The variables include the volume fractions of crimpedsteel fibres (Vfs), viz. 0.5% (39.25 kg/m3) and 1% (78.5 kg/m3) andvolume fractions of polypropylene fibres (Vfp), viz. 0.10% (0.9 kg/m3), 0.15% (1.35 kg/m3) and 0.20% (1.8 kg/m3). The beam and col-umn have the same cross section of 150 � 200 mm. The columnwas reinforced with four 10 mm diameter high yield strength de-formed (HYSD) bars and the beam was provided with two10 mm diameter HYSD bars at top and bottom. HYSD bars of6 mm diameter were used as transverse ties in columns and stir-rups in beams. The overall dimensions and details of reinforcementare shown in Fig. 2. The mechanical properties of the reinforce-ments are as given in Table 3. Two specimens were tested in eachseries and average of the results was taken for analysis. Details oftested specimens and variables are given in Table 4.

3.4. Testing

The test setup consisted of a steel loading frame with a capacity300 kN. The specimens were tested in an upright position in theloading frame after 28 days of curing. The schematic diagram ofthe test setup is shown in Fig. 3. The bottom end of the columnwas simply supported and the top was a hinged support, whichwas simulated by a steel ball placed between the grooves of twosteel plates. An axial compressive load of 20% of the axial capacityof the column was applied on the column by means of a hydraulicjack so as to make it stable [6]. The beam tip was subjected to re-verse cyclic loading through 500 kN hydraulic jack connected to

Fig. 1. Fibres used.

Table 1Properties of fibres.

Type of fibre Length(mm)

Diameter(mm)

Aspectratio

Ultimate tensilestrength (MPa)

Crimped steelfibres

30 0.45 66 800

Polypropylenefibres

12 0.038 316 550–600

Table 2Mix proportion for M60 grade HPC.

Particulars Quantity (kg/m3)

Cement 403Fly ash 112Silica fume 45Sand 603Coarse aggregate 1043Water 158Superplasticizer 11.76

688 N. Ganesan et al. / Materials and Design 54 (2014) 686–693

the load cell through the plunger of the jack. Fig. 4 shows the testsetup.

The specimens were loaded up to a certain magnitude, then un-loaded in the negative direction and reloaded so that a full cycle ofreverse loading can be obtained. After each cycle the magnitude of

Fig. 2. Details of r

loading was increased. This process was continued till the failure ofthe joint. At each stage of loading, the deflection at the tip of beamwas measured using a dial gauge having least count of 0.01 mmand 50 mm travel. The strain in the beam as well as the columnreinforcements were measured using the six strain gauges in-stalled in each beam–column joint. So as to ensure accuracy inthe measurement of deformations, four LVDTs having a gaugelength of 200 mm were used in addition to the strain gauges tomeasure the beam and joint rotations. The widths of cracks weremeasured at regular intervals using a crack detection microscopeof 25� magnification.

3.5. Behaviour of specimens

Fig. 5 shows the crack pattern of the specimens at failure. In allthe specimens, the first crack was observed at the junction be-tween beam and column. Further increase in loading resulted inadditional cracks on the beam portion and propagation of someof the initial cracks. Finally the cracks widened leading to the fail-ure of the joint. Most of the cracks were concentrated in the beamportion near the column. No cracks were seen on columns duringthe test and joint shear failure did not occur in all the specimens.HPC specimens were observed to have wider cracks when com-pared to the fibre reinforced specimens. In the case of SFRHPCand PFRHPC specimens, more number of finer cracks was formed.For HFRHPC specimens the behaviour was similar to that ofSFRHPC specimens. However, the cracks formed were much finerthan that formed in SFRHPC. This can be attributed to the com-bined effect of polypropylene and steel fibres to control the cracks

einforcement.

Table 3Properties of deformed reinforcement bars.

Nominaldiameter of bar(mm)

Actualdiameter ofbar (mm)

YieldStrength(MPa)

UltimateStrength(MPa)

Modulus ofElasticity(GPa)

10 9.97 432 567 2236 6.16 424 624 230

Table 4Details of specimens.

Sl. No. Designation of specimens Volume fraction of fibres (%)

Steel Polypropylene

1 HPC 0 02 PFRHPC1 0.103 PFRHPC2 0.154 PFRHPC3 0.20

5 SFRHPC1 0.5 06 HFRHPC1 0.107 HFRHPC2 0.158 HFRHPC3 0.20

9 SFRHPC2 1 010 HFRHPC4 0.1011 HFRHPC5 0.1512 HFRHPC6 0.20

Fig. 4. Test setup.

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at both micro and macro level. The polypropylene fibres arrest themicro cracks and hence control the formation of macro cracks,while the steel fibres restrict the widening of macro cracks and in-crease the energy absorption capacity of the composite [28].

4. Results and discussion

4.1. Load deflection behaviour

Fig. 6 shows the typical load deflection plots of HPC, PFRHPC,SFRHPC and HFRHPC specimens tested under reversed cyclic load-ing. The load–deflection hysteresis obtained for the joints was sim-ilar to that obtained in [7] for steel fibre reinforced concrete. Forcomparison and better representation the envelopes of the hyster-esis of all the specimens plotted in a single graph, as shown in

Fig. 3. Schematic diag

Fig. 7. Envelope curves were obtained by joining the peak pointsof all the cycles. Using these envelopes the first crack load, energyabsorption capacity and ductility factor for the specimens were ob-tained and listed in Table 5.

It can be observed from Fig. 7 that in HFRHPC, the ultimateload and the corresponding deflection of specimens were in-creased as the hybrid fibre content increases. This could be attrib-uted to the ability of these fibres in arresting the micro cracks aswell as macro cracks. As and when micro cracks develop in thematrix, the polypropylene fibres in the vicinity of such microcracks will try to arrest these cracks and prevent further propaga-tion. After the formation of cracks steel fibres intercept them andthe bridging action of fibres reduces the widening of cracks. Alsothe cracks have to take a meandering path due to the interceptionof fibres which results in the demand of more energy for furtherpropagation of cracks; this in turn increases the ultimate load.However, at higher percentages of polypropylene fibre content,in fact, a reduction in strength has been found. This may bedue to reduced workability of concrete at higher fibre contentsdue to the balling effect of fibres. Similar observations was alsomade by other researchers when the polypropylene fibre contentwas more than 0.15% [10].

ram of test setup.

Fig. 5. Crack pattern of specimens.

-30

-20

-10

0

10

20

30

-30 -20 -10 0 10 20 30

Loa

d (k

N)

Deflection (mm)

HPC

-30

-20

-10

0

10

20

30

-30 -20 -10 0 10 20 30

Loa

d (k

N)

Deflection (mm)

PFRHPC3

-30

-20

-10

0

10

20

30

-30 -20 -10 0 10 20 30

Loa

d (k

N)

Deflection (mm)

SFRHPC2

-30

-20

-10

0

10

20

30

-30 -20 -10 0 10 20 30

Loa

d (k

N)

Deflection (mm)

HFRHPC5

Fig. 6. Typical load–deflection plots.

690 N. Ganesan et al. / Materials and Design 54 (2014) 686–693

4.2. First crack load and ultimate load

The first crack load and the ultimate load of the specimens aregiven in Table 5. First crack load was determined from the envelopcurve of the load deflection plot corresponding to the point atwhich the curve deviated from linearity. From the table it can be

observed that first crack load increased with increase in fibre con-tent, which may be due to the increase in tensile strain carryingcapacity of concrete in the neighbourhood of fibres. The first crackload increased by 18% for PFRHPC and 31% for SFRHPC specimens.It has been found that addition of hybrid fibres increases first crackload by 37% and ultimate load by 62% for HFRHPC specimen with

Fig. 7. Envelope of Load–deflection plots.

Table 5Test results.

Designation ofspecimen

First crackload(kN)

Ultimate load (kN) Deflection underultimate load (mm)

Forwardcycle

Reversecycle

Forwardcycle

Reversecycle

HPC 8.00 16.00 16.05 15.40 15.87PFRHPC1 8.50 18.00 18.00 19.17 16.80PFRHPC2 9.00 19.20 18.00 20.87 19.53PFRHPC3 9.50 18.00 19.45 16.35 20.48

SFRHPC1 10.00 18.00 19.80 19.20 20.46HFRHPC1 9.50 20.00 18.00 20.68 14.83HFRHPC2 10.00 20.40 18.00 21.01 14.27HFRHPC3 9.50 22.00 20.00 20.81 18.52

SFRHPC2 10.50 20.00 22.00 19.87 21.56HFRHPC4 10.50 24.00 22.00 23.83 22.17HFRHPC5 11.00 26.00 24.00 26.07 23.54HFRHPC6 10.00 21.50 22.00 17.28 20.25

Table 6Energy absorption capacity and displacement ductility.

Designation ofspecimen

Energy absorptioncapacity (kNm)

dy

(mm)du

(mm)Displacementductility factor, w

Forwardcycle

Reversecycle

Absolute Relative

HPC 0.142 0.156 12.50 15.87 1.27 1.00PFRHPC1 0.222 0.199 13.00 19.17 1.47 1.16PFRHPC2 0.263 0.236 12.00 20.87 1.74 1.37PFRHPC3 0.192 0.283 11.50 20.48 1.78 1.40

SFRHPC1 0.241 0.275 11.00 20.46 1.86 1.47HFRHPC1 0.289 0.193 9.50 20.68 2.18 1.71HFRHPC2 0.303 0.184 10.00 21.01 2.10 1.66HFRHPC3 0.323 0.274 7.50 20.81 2.77 2.19

SFRHPC2 0.285 0.353 9.50 21.56 2.27 1.79HFRHPC4 0.424 0.381 8.50 23.83 2.80 2.21HFRHPC5 0.512 0.441 6.50 26.07 4.01 3.16HFRHPC6 0.244 0.324 8.00 20.25 2.53 1.99

N. Ganesan et al. / Materials and Design 54 (2014) 686–693 691

1% (78.5 kg/m3) steel fibres and 0.15% (1.35 kg/m3) polypropylenefibres when compared to specimen without fibres.

4.3. Energy absorption capacity and displacement ductility

The area under the load deflection curve indicates the energyabsorption capacity. Energy absorption capacity was calculatedand the values obtained are given in Table 6. From the Table itcan be seen that energy absorption capacity consistently increasesand it is maximum for HFRHPC specimen with 1% (78.5 kg/m3)steel fibres and 0.15% (1.35 kg/m3) polypropylene fibres, which isapproximately 3.6 times higher than that of HPC joints.

It is required that an earthquake resistant structure should becapable of deforming in a ductile manner when subjected to lateralloads in several cycles in the elastic range. Ductility of a structure isits ability to undergo deformation beyond the initial yield defor-mation, while still sustaining load. The ductility factor which is ameasure of ductility of a structure is defined as the ratio of maxi-mum deflection (du) to the deflection at yield (dy). The ductility fac-tors were calculated and the results obtained are given in Table 6.The details of the procedure adopted are described elsewhere [22].

The values in Table 6 show that the fibres present in the mix-tures influence the energy absorption capacity and ductility. Com-pared to HPC specimen the ductility factor is increased by 3.1 times

4

5

mm

)

HFRHPC6HFRHPC5HFRHPC4SFRHPC2

692 N. Ganesan et al. / Materials and Design 54 (2014) 686–693

for HFRHPC specimen with 1% (78.5 kg/m3) steel fibres and 0.15%(1.35 kg/m3) polypropylene fibres. The deflection at ultimate loadwas also higher for HFRHPC specimens.

0

1

2

3

0 2 4 6 8 10 12 14

Stif

fnes

s (k

N/

Loading Cycle

HFRHPC3HFRHPC2HFRHPC1SFRHPC1PFRHPC3PFRHPC2PFRHPC1HPC

Fig. 9. Stiffness degradation plots.

4.4. Energy dissipation capacity

Energy-dissipation capacity is an important indicator of theseismic properties of a structure. The structures can withstandstrong ground earthquake motions only if they have sufficient abil-ity to dissipate seismic energy. This energy dissipation is providedmainly by inelastic deformations in critical regions of the struc-tural system and requires adequate ductility of the elements andtheir connections [29]. It can be estimated from the area withinthe load–displacement hysteretic loop for every cycle of load.The cumulative energy dissipated by the specimens was calculatedby summing up the energy dissipated in consecutive load displace-ment loops throughout the test. The cumulative energy dissipationof the specimens during each cycle is shown in Fig. 8. Figure clearlyshows that all FRC specimens had higher cumulative energy dissi-pation than the reference HPC specimen without fibres. A similarbehaviour was reported by other researchers [7] in which all steelfibre reinforced specimens showed a consistent increase in energydissipation as the fibre content increases. Around 5 times improve-ment in cumulative energy dissipation was exhibited by theHFRHPC specimens containing 1% (78.5 kg/m3) steel fibres and0.15% (1.35 kg/m3) polypropylene fibres when compared to speci-men without fibres. The improvement in energy dissipation for theHFRHPC specimens was attributed to their enhanced ductilebehaviour.

4.5. Stiffness degradation

Application of cyclic or repeated loading on the RCC beam–col-umn joint causes reduction in the stiffness of the joint. This reduc-tion in stiffness of the specimens can be assessed by computing thesecant stiffness which provides a measure of the stiffness degrada-tion in the specimens [6,30]. The secant stiffness in each cycle wascalculated using a line drawn between the maximum positive dis-placement point in one half of the cycle and the maximum nega-tive displacement point in the other half of the cycle [30]. Fig. 9shows the stiffness degradation trends for the beam column jointspecimens. It may be noted that the HPC specimen has the lowestinitial stiffness and shows a quick reduction in secant stiffness val-ues. In PFRHPC specimens, the stiffness degradation trend was al-most similar to that of HPC. This may be due to the low modulus ofelasticity of polypropylene fibres which could not contribute muchto the stiffness of HPC. However, the addition of steel fibres was

0

100

200

300

400

500

600

700

800

0 5 10 15 20Cum

ulat

ive

Ene

rgy

diss

ipat

ion

(kN

mm

)

Load cycle

HFRHPC6

HFRHPC5

HFRHPC4

SFRHPC2

HFRHPC3

HFRHPC2

HFRHPC1

SFRHPC1

PFRHPC3

PFRHPC2

PFRHPC1

HPC

Fig. 8. Cumulative energy dissipation.

seen to decrease the rate of degradation of stiffness when com-pared to polypropylene fibres. The use of hybrid fibres significantlyincreased the initial secant stiffness value of the specimens andprovided a stable reduction in stiffness up to failure. This can beattributed to the combined effect of hybrid fibres to control thecracks at both micro and macro level. As the number of cycles in-crease, micro-cracks develop, and the large number of tiny poly-propylene fibres bridges the cracks at micro level and the steelfibres intercept the macro cracks and control the widening of thesecracks. This action will control further propagation of cracks andwill result in higher energy demand for debonding and pull-outof fibres in the vicinity of cracks. During this process, stiffness ofspecimens with fibres will not undergo much reduction. These re-sults are consistent with the previous published literature [6],where the joint with steel fibres exhibited decreased rate of stiff-ness degradation when compared to that without fibres. However,addition of hybrid fibres improved the initial stiffness of the joint.

5. Conclusions

The load deflection characteristics, energy dissipation, ductilityand stiffness degradation of hybrid fibre reinforced beam columnjoints subjected to reverse cyclic loading were investigated. The re-sults indicate that the use of hybrid fibres could enhance thestrength and ductility of beam column joints significantly. Theexperimental results lead to the following conclusions:

(1) The HFRHPC beam column joint showed a significantincrease in first-crack strength and ultimate strength, as wellas better ductility and energy-dissipation capacity.

(2) Energy absorption capacity and displacement ductility factorincreased by 3.6 times and 3.1 times respectively forHFRHPC specimen with 1% (78.5 kg/m3) steel and 0.15%(1.35 kg/m3) polypropylene fibres when compared to HPC.

(3) It is possible to reduce the congestion of steel reinforcementin the beam–column joints by using HFRHPC and thisreduces the construction difficulties.

(4) Ductility is one of the basic parameters considered in theseismic design of structures. The development of a high per-formance material like HFRHPC, that possess enhanced duc-tility, energy absorption and strength would allow structuralengineers an alternative for the design of critical regionssuch as beam column joints in earthquake resistant struc-tures. By using this highly ductile material, rigorous seismicreinforcement detailing which leads to congestion of steelcan be avoided in beam column joints. The load displace-ment relationships obtained in this study, would be helpfulfor getting the capacities at deflections corresponding toultimate and serviceability stages of HFRHPC beam columnjoints. The fore mentioned behaviour will be useful in therational design of structures subjected to unforeseenloading.

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