Strength of Epoxy-Coated Reinforcing Bar Splices Confined With Transverse Reinforcement

8/11/2019 Strength of Epoxy-Coated Reinforcing Bar Splices Confined With Transverse Reinforcement

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ACI STRUCTURAL JOURNAL TECHNICAL PAPER

Title no 90 810

Strength of Epoxy Coated Reinforcing Bar Splices Confined

with Transverse Reinforcement

by B S Hamad and J 0 Jirsa

This paper determines the effect of epoxy-coated transverse reinforcementon the strength of epoxy-coated ba r splices. Existing recommendations fordesign of splices and anchorage o f epoxy-coated reinforcement were reviewed and modifications were suggested.

Twelve beams were tes ted in negative bending with multiple splices in aconstant moment region at the center of the beam. All bars were cast in atop bar position with more than 12 in. 30 em) of concrete below the bars.Companion specimens were identical except for bar coating. The prime variable was the amount of ransverse reinforcement crossing the splitting planein the splice region. Other variables included bar size [No. 6 19 mm) andNo. I I 36mm)] and bar spacing. The nominal coating thickness of all epoxycoated bars was 8 mils 0.2 mm). Failure of all beams was governed by splitting o f he concrete cover in the splice region.

Test results indicated that the presence of ransverse reinforcement in the

splice region increased deformation capacity of he beams an d improved anchorage strength of epoxy-coated bar splices relative to uncoated bar splices.The improvement was independent o f he number o f splices, bar size, or barspacing. Using results o f his study an d results of other tests on epoxy-coatedbar splices in the literature, a comprehensiv e review of he effect of epoxycoating on structural aspects of epoxy-coated bar splices was performed. Design equations were recommended, and modifications to the ACI BuildingCode AC 318-89) development and splice length provisions were suggested.

Keywo rds: anchorage (structural); bonding; detailing; epoxy resin s; lap connections;reinforcing materials; splicing.

Corrosion of reinforcing steel in concrete is the mostcommon cause of premature deterioration of reinforced con

crete structures. The corrosion problem continues to drain resources of owners of reinforced concrete structures in bothpublic and private sectors in the United States and throughoutthe world.

Of the many methods of corrosion protection possible, fusion-bonded epoxy coating often offers one of the best combinations of protection, ease of use, and economy. The purpose of epoxy coating is to prevent chlorides from reachingthe steel surface. A very important consideration in the useof epoxy-coated reinforcing bars is the effect of the coatingon the strength of bond between reinforcing bars and concrete. Most codes prohibit any nonmetallic coatings frombeing applied to reinforcing bars, which may decrease thebond capacity by preventing adhesion between the bar and theconcrete. ACI 318-89 1 Section 7.4.1 states that bars shouldbe free of nonmetallic coatings, mud, or oil which may de-

ACI Structural Journal January February 1993

crease the bond capacity. Epoxy coatings, however, are permitted by Section 7.4.1. Section 3.5.3.7 states that epoxycoated reinforcing bars should comply with Standard Specification for Epoxy-Coated Reinforcing Steel Bars (ASTMA 775). 2

Since the Federal Highway Administration approved theuse of epoxy coating in the early 1970s, epoxy-coated barshave been used in nearly all types of structures where concrete is exposed to a corrosive environment. Epoxy-coatedbars are used in the decks, shafts and foundations, piers, bentcaps, and other bridge-supporting elements. Other applications include sewage and water treatment plants, coolingtowers and other parts of power plants, chemical plants,parking garages, refineries, subways, reinforcement for earthretention, and continuously reinforced concrete pavements.

Before ACI 318-89 1 was issued, epoxy coating was usedwithout much concern about the anchorage characteristics ofepoxy-coated bars. Bond stresses and bond strength will beused in this paper to permit comparisons of test results. Thebond stress developed by an anchored bar is simply the forcedeveloped in the bar divided by the surface area of the bar.Although development lengths are used in design, they donot permit a meaningful comparison of test data when anchorage length is shorter than that needed to develop yield.

Test data available prior to the 1989 ACI Building Codeindicated that reduction in bond strength of epoxy-coated barswas not excessive.3.4 Based on more recent studies of the bondstrength of epoxy-coated bars,s the basic development lengthfctb of a deformed bar (Section 12.2.4.3) was modified to account for epoxy coating. For bars with cover less than 3db orclear spacing between the bars less than 6db the developmentlength is multiplied by a factor of 1.5. The factor is 1.2 for allother conditions. Moreover, Section 12.2.4.3 specifies that inthe case of a top bar, defined as a horizontally cast bar with

ACI Structural Journal, V 90, No. I, January-February 1993. . . .Received Sept. 16, 1991, and r e v i e ~ e dunder Ins titut e publicatiOn j)Ohces. COjJY-

right 1993, American C o ~ c r e t eInstitute. All ngh ts r ~ s e r v e d1 ~ c l u d m gthe makingof copies unless penmsswn IS obtamed from the co pynght propnetor.s. Pertment diS-cussion will be published m the November-December 1993 ACI Structural Journal Ifreceived by July I, 1993.

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Bilal S. Hamad is an assistant professor on the Faculty of Engineering and Architec-ture at the American University of Beirut Lebanon. He received his BE degree fromthat university and his MS and PhD degrees from the University of Texas at Austin. Hisresearch interests include plain concrete and design and behavior of reinforced con-crete structures.James 0 Jirsa FACI is the Janet S Cockrell Centennial Professor of Engineering atthe University of Texas at Austin. He is a member of ACI Committees 3/8 StandardBuilding Code; and 408 Bond and Development of Reinforcement.

more than 12 in. 30 em) of concrete cast below the bar, theproduct of the 1.3 factor for top reinforcement and the factorfor epoxy-coated reinforcement should not be greater than1.7.

It has been well established that the anchorage strength ofuncoated bars is improved substantially by adding transversereinforcement. However, in most previous studies of epoxycoated bar splices, 5-7 the effect of transverse reinforcementwas not investigated. One objective of this study was to assess the effect of transverse reinforcement on the bond characteristics of epoxy-coated bar splices relative to uncoated

bar splices. Another objective was to use the results of thisstudy and results of other tests on epoxy-coated bar splicesin the literature 57 to perform a comprehensive review of theeffect of epoxy coating on the structural aspects of epoxycoated bar splices. A third objective was to develop or revise the existing) design recommendations for splice lengthand development length of straight epoxy-coated bars.

PREVIOUS STUDIES OF EPOXY COATED BARSPLICES

University of Texas exploratory studies

In an exploratory research program conducted at the University of Texas by Treece and Jirsa,s 21 beams were testedin 9 series. The variables were bar size [No.6 19 mm) andNo. 11 36 mm)], concrete strength [4, 8, and 12 ksi 28, 55,and 83 MPa)], casting position, and coating thickness [5 and12 mils 0.13 and 0.3 mm)]. In each series, a different combination of variables was examined, but the only variablewithin a series was the coating thickness on the bars.

The beams were tested in negative bending. Each beam included three bars in tension, all spliced at the center. Thesplice lengths were selected so that the bars would fail in bondbefore reaching yield. All the bars of each size were from the

same heat of Grade 60 414 MPa) steel and had a diamonddeformation pattern. No transverse reinforcement was provided in the splice region.

In each test, the mode of failure was a splitting failure inthe splice region. Test results showed that epoxy-coated barswith an average coating thickness above 5 mils 0.13 mm) developed 67 percent of the bond strength of uncoated bars witha standard deviation of 9 percent. The reduction in bond wasconsistent for the range of variables considered in the study.Therefore, epoxy-coating was the only variable that causedreduction in bond strength.

University of California at Berkeley testsIn 1989, DeVries and Moehle6 reported an experimental

study in which 36 beams were tested in 9 series. The first se-

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ries was a pilot series that did not include epoxy-coated bars,and each of the next eight series included two uncoated barspecimens, one with bottom-cast bars and one with top-castbars, and two similar epoxy-coated bar specimens. Besidescasting position, other variables included bar size [No.6 19mm) and No.9 28 mm)] and the presence of an antibleedingagent in the concrete.

Each beam had two longitudinal bars spliced at the centerwith No. 3 10-mm) stirrups provided along the splice length.The splice length was designed to result in a splitting failurebefore yielding of the bar. All bars of each size came fromthe same heat of Grade 60 414 MPa) steel and had a bambooparallel) deformation pattern except for the pilot series,

which had a chevron pattern. The epoxy coating was nominally 8 mils 0.2 mm) thick. The beams were tested in negative bending, and the mode of failure was a splitting failureat the splice region for all beam tests. .

Test results indicated that epoxy-coated bars developed 84percent of the bond strength of uncoated bars with a standarddeviation of 10 percent. Based on the test results, De Vries

and Moehle indicated that the effectsof

casting position andepoxy coating were not cumulative, and that the modification for top-cast epoxy-coated bars relative to bottom-castepoxy-coated bars, given in Section 12.2.4.3 of the 1989 ACIBuilding Code ACI 318-89), 1 was not needed. Moreover, thetest results showed that the presence of an anti bleeding agentin the concrete did not significantly alter the bond stress ofthe splice for either top or bottom-cast bars.

University of Kansas testsIn 1990, Choi et a1.7 reported a series of 15 beams tested

in negative bending with multiple splices in the middle and

no stirrups in the splice region. The variables were bar size[No. 5, 8, and 11 16, 25, and 36 mm)] and bar deformationpattern. The mode of failure in all tests was splitting of theconcrete cover in the splice region. Test results indicated thatthe ratio of the bond strength of epoxy-coated bar splices tothat of uncoated bar splices bond ratio) varied from 0.54 to0.94 with an average value of 0.83 and a standard deviationofO.l.

EXPERIMENTAL PROGRAMTest specimens

In the research program reported in this paper, 12 beams

3 series) with multiple splices at the center of the beam weretested in negative bending. The variables were bar size, barspacing, and amount of transverse reinforcement in the spliceregion.

The test parameters for each specimen are shown in Table1. A five-part notation system was used to identify the variables of each beam. First, the beam is identified in the sequence in which it was tested. Second, the bar size [No.6 19mm) or No, 11 36 mm)] is noted. Third, the nominal concrete strength 4 ksi) is identified. Fourth, uncoated U) orepoxy-coated C) bars are noted. The digit 3 following theletter U or C refers to the presence of three splices instead of

two splices, as in the first six beams. The fifth portion indicates the presence of transverse reinforcement in the spliceregion, where U represents uncoated ties and C denotesepoxy-coated ties. The number following U or C is the av-

ACI Structural Journal I January February 1993


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Table 1 Details of beam tests

Coating thickness

Series Specimen db Jc e Nominal, Average, Cb, 2 X Cs, Splice regionnumber notation in. ksi in. mils mils in. in. stirrups

B-1-11-4-U 1.41 3.7 30 - - 2 4.00 -B2-II-4-C 1.41 3.7 30 8 8.0 2 4.00 -

Series B3-11-4-U-UIO 1.41 3.7 30 - - 2 4.00 3 3@ lOin.one B4-II-4-C-C 10 1.41 3.7 30 8 8.6 2 4.00 3 3@ lOin.

B-5-11-4-U-05 1.41 4.0 30 - - 2 4.00 6 3@ 5 in.B6-II-4-C-C5 1.41 4.0 30 8 8.8 2 4.00 6 3@ 5 in.

Series B7-11-4-U3-U5 1.41 4.0 30 - - 2 1.41 6 3@ 5 in.two B 8-II-4-C3-C5 1.41 4.0 30 8 8.6 2 1.41 6 3@ 5 in.

B9-6-4-U3 0.75 3.74 18 - - 2 1.25 -

Series BI0-6-4-C3 0.75 3.74 18 8 6.8 2 1.25 -three BII-6-4-U3-U6 0.75 3.74 18 - - 2 1.25 3 3@ 6in.

B 12-6-4-C3-C6 0.75 3.74 18 8 6.7 2 1.25 3 3@ 6in.

I ksi 6.895 MPa; I in.= 25.4 mm; I mil= 0.025; 3 bar= IO-mm diameter.

erage spacing of the ties along the splice length. The absenceof a fifth portion in the notation of a beam indicates that transverse reinforcement was not present in the splice region. Asan example of the notation system, BS-11-4-U-US indicatesthat the fifth beam tested included two No. 11 (36-mm) uncoated bar splices, had a nominal concrete strength of 4 ksi(28 MPa), and included uncoated ties at an average spacingof 10 in. (25 em) in the splice region. A concrete cover of 2in. (5 em) to the reinforcing bar was chosen as a typical sideand top cover for all the beams.

In the six beams of the first series, two No. 11 (36-mm) bar

splices were designed so that the side cover, 2 in. (5 em), wasone-half the clear spacing between splices, 4 in. ( 10 em), andequal to the top cover. This allowed identical confinement forboth splices by concrete and by any ties crossing the splittingplane. With 2-in. cover and 4-in. clear spacing, the beamwidth was 13.5 in. (34 em). The two beams of the second series were designed with three No. 11 (36-mm) bar splices,and the four beams of the third series had three No. 6 ( 19-mm)bar splices. These clear spacings were at or near the minimumvalues allowed in codes. The beam widths were 15.5 in. (39em) and 11 in. (28 em) in the second and third series, respectively. The cross-sectional details of all beams are shown

in Fig. l The depth of all specimens was 16 in. (41 em). Thebars were cast in a top position with more than 12 in. (30 em)of concrete cast below the bars.

The loading system was designed to produce a constantmoment region in the middle of the beam. Reinforcing barswere spliced at midspan. The splice length was determinedto develop a steel stress Is less than yield, using an empiricalequation developed by Orangun, Jirsa, and Breens

db[__ ._ -so].f]Zfs

= ,c1.2 3- Ktrdb

K - arr fyr < 3 0 d < 2 5rr - _ . a n 500sdb db

ACI Structural Journal I January-February 1993

1)

13.534mm)

SERIES ONE:81, 82, 83,84,85,86

2 db db 2 15cm)0 0 0 0 0 0

s3 11 bars 41cm)

15.5 39mm)

SERIES TWO:87,88

Fig. ]-Cross-sectional details o f beam specimens

where arr = he area of transverse steel crossing the plane ofsplitting. The splice length was set at 30 in. for all No. 11 (36-mm) bars and 18 in. ( 46 em) for the No. 6 ( 19-mm) bars. Theoverall lengths of the No.6 (19-mm) and No. 11 (36-mm) barspecimens were 13 and 21 ft (5 and 6.4 m), respectively (seeFig. 2).

Materials

Bars ofeachsize,No. 6 (19mm)andNo. 11 (36mm), werefrom the same heat of steel and had a parallel (bamboo) deformation pattern. This insured that both uncoated and coatedbars in companion specimens had identical rib geometry andmechanical properties. The bars met ASTM A 615-87a9 andwere Grade 60 (414 MPa). The nominal coating thickness ofthe epoxy-coated bars was 8 mils (0.2 mm). The thickness ofthe coating was measured with a dry film thickness gage

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l ' l . . , s ; ' l ' l ~ > - - - 4 ' - _ o _ - t + - - . : . . . . _ - ~ - - - . . , ' f " l ~ - + ~ l ( 1 5 c m )Shear ShearSpan oment Span

p p

i"'-l"l+----+ ot----9-'0_"...:.(2_.7_4_m...:.) - t i + - s - - _ s _ - l . , * l t : l > l 6 ~15cm)onstant Shearoment Span

Fig. 2 Dimensions and test setup of beam specimens

(Type 1, magnetic pulloff). The average coating thickness for

each epoxy-coated bar specimen is shown in Table 1. The average coating thickness for the epoxy-coated transverse reinforcement was approximately 9 mils (0.23 mm).

A non-air-entrained mix was used. Assuming saturated surface dry conditions for the aggregates, the mix proportions (inlb) were as follows: cement (Type I), 360 (1600 N); coarseaggregate, 188 (836 N); sand, 1435 (6380 N); water, 266(1180 N); and water reducer-retarder, 10.5 oz (310 cm3). Before casting, additional water was added until a slump of about3 0 in. (7.5 em) was reached. The concrete compressionstrength for each specimen is listed in Table 1.

Test procedureLoad was applied gradually in 1-kip increments until

failure occurred. At each load stage, deflection readings weretaken, and flexural cracks were marked and measured usinga crack width comparator. Additional details of the test program and results are given in Reference 10.

SPECIMEN BEH VIOR AND N LYSIS OF TESTRESULTS

General behaviorIn all specimens, the mode of failure was splitting of top

concrete cover at the tension face of the splice region, or sideconcrete cover in the plane of the splices (side split failure),or both top and side covers (face-and-side split failure).

First flexural cracks in all beams occurred randomly in theconstant moment region on the tension side of the beams outside the splice. As loading continued, cracks formed alongthe entire length of the constant moment region including thesplice. Most of the flexural cracks on the tension side of thebeam extended into side faces. In beams with no stirrupscrossing the splitting plane, flexural cracks formed randomlyin the splice region. On the other hand, in beams with stirrupsin the splice region, flexural cracks generally formed at stirruplocations.

Failure of beams with no stirrups in the splice region wassudden. Load dropped completely after reaching ultimate. For

8

beams with stirrups in the splice region, failure was gradual.The load dropped slightly after reaching ultimate and continued to drop gradually with increasing deflection. After thetest was halted, the top and side concrete covers were removedto reveal the failure plane in the splice region. In general, itwas more difficult to remove the cover in the uncoated thanin the epoxy-coated beams. After the cover was removed,concrete deposits were left on the sides of the bar deformations of uncoated bars, whereas the epoxy-coated bars werevery clean. While the grooves left in the concrete cover bythe uncoated bars were dull and worn in appearance, the concrete in contact with the epoxy-coated bars had a smoothglassy surface, as if a bond-breaker had been applied.

Crack width and spacingThe results indicated that average flexur_al crack width in

the constant moment region outside the splice length waslarger in epoxy-coated bar specimens than in companion uncoated bar specimens at the same level of stress. As shown

in Table 2, at a given steel stress level, specimens with epoxycoated bars had fewer cracks (wider spacing) but the crackswere wider than in specimens with uncoated bars. The crackwidth ratio is the average crack width of an epoxy-coated barspecimen divided by that of the companion uncoated bar specimen.

Beam stiffnessThe stiffness of beams with epoxy-coated bars was com

pared to that of beams with uncoated bars by plotting steelstress versus end deflection for each beam specimen. Steel

stress-deflection curves for all specimens in the first seriesare shown in Fig. 3. As shown in the curves, there was littledifference in initial stiffness between uncoated and the companion epoxy-coated bar specimens. However, as failure loadis approached and as the amount of transverse reinforcementin the splice region increases, curves separate, with the coatedbar specimen showing a gradual decrease in stiffness relativeto the uncoated bar specimen.

Bond strengthBond strength was based on an average stress along the

length of the splice. To evaluate the bond stress u the totalforce developed in the bar Ab/s was divided by the surfacearea of the bar along the splice length 1tdbfs

2)

Steel stress s was determined using a beam cracked sectionanalysis. The maximum load Pmax the calculated ultimatesteel stress su and the corresponding bond stress Ut and bondratio are listed for each beam in Table 3. The bond ratio is thebond stress of the epoxy-coated bar specimen divided by thatof the companion uncoated bar specimen.

Bond capacity of No 6 (19-mm) and No. 11 (36-mm) barsplices improved as the amount of transverse reinforcementcrossing the splitting plane in the splice region increased.Such reinforcement provides the concrete in the plane of thesplices with more confinement and resistance against split-



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Table 2 Comparison of average crack widths of beam specimens

Series Specimen Number ofnumber notation cracks

81-11-4-U 6

82-11-4-C 4

83-11-4-U-01 0 4Series one84-11-4-C-CJO 4

85-11-4-U-05 8

86-11-4-C-C5 5

87-11-4-U3-U5 4Series two

88-11-4-C3-C5 4

89-6-4-03 4

B10-6-4-C3 2Series three

B11-6-4-U3-U6 3

B 12-6-4-C3-C6 2

I ksi = 6.89 MPa; I mil= 0.025 mm.

ting. The improvement in bond strength was greater forepoxy-coated bar splices than uncoated bar splices. Resultslisted in Table 3 indicate that the bond ratio of coated to uncoated No. 11 (36-mm) bar splices increased from 0.74 in theabsence of ties in the 30-in. (76-cm) splice region to 0.81when three No. 3 (10-mm) ties were provided, and to 0.84when six No. 3 (10-mm) ties were provided. On the otherhand, the bond ratio of coated to uncoated No.6 (19-mm) barsplices improved from 0.67 in the absence of splice region tiesto 0.74 when three No.3 (10-mm) ties were placed in the 18-

in. (46-cm) splice region.The improvement in the bond capacity of epoxy-coated bar

splices relative to uncoated bar splices, with ties in the spliceregion, was independent of the number of splices, bar size,or bar spacing.

Evaluation of bond splice testsBeams with no stirrups in splice region-Four beams with

no ties in the splice region were tested in this study B 1, B2,B3, and B4). All the beams included in Treece and Jirsa'sstudys and in the study reported by Choi et aU had no ties inthe splice region.

Measured bond strength of each beam was compared withthe bond stresses implied by the current ACI Building Code(ACI 318-89) 1 specifications for calculating splice lengths.Taking R s= 1.3 R db according to Section 12.15 of the code, andusing the equation given in Section 12.2.2 with the limit specified in Section 12.2.3.6 gives the following

0.04Abfy db/yR s = 1 .3 f db , fidb = r7 : : 0.03 r- '

-vi -vf{11 100 psi (3)

( - 0.02Abfy > db/y IF'< 0 69 MPt d b {11 _ 8 {11 , JJc _ . a

Combining the preceding equations with undb = Abfy


K,,

0

0

1.021.02

2.04

2.04

1.36

1.36

0

0

2.13

2.13

Crack width comparison

Steel Crackstress Average width ratio,level, crack width, coated/

ksi mils uncoated

23 7.2 -23 10.4 1.44

29 12.0 -29 11.0 0.92

33 11.4 -33 18.4 1.61

27 10.1 -27 24.5 2.43

30 4.0 -

30 7.4 1.85

30 4.7 -

30 7.8 1.70

45300

40 10 20 30 mm)

CJ)30n 200w

MPa:1- 20n. .J 81-11-4-U 100w 10w 82-11-4-C1- n

0

4530040

CJ)30n 200w

MPa:1- 20n.J 100w 10w

1- n

0

4540

CJ)n 30

wa: MPa1-

20n. .Jw 101- n

00 0 0 4 0 8 1.2 1.6

DEFLECTION, Inches

Fig. Variations of steel stress versus end deflection, SeriesOne

u =6.12 fl 6.41{71, {11 100 psidb

( u = 13 fJ 0.5{11, {11 0.69 MPa (4)The modification factor for top-cast bars is 1.3 according to

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Table 3 Te s t results of beam specimens

Series Specimennumber notation cldb

B1 ll 4U 1.42

B2 ll 4 C 1.42

Series B3 ll 4 U Ul0 1.42

one B4-11-4-C-C10 1.42

B5-11-4-U-U5 1.42

B6-11-4-C-C5 1.42

Series B7 ll 4 U3 U5 0.50two B8-11-4-C3-C5 0.50

B9-6-4-U3 0.83

Series B10-6-4-C3 0.83three Bll 6 4 U3 U6 0.83

B 12-6-4-C3-C6 0.83

*Bond rati o= u (coated) I u (uncoated).I ksi = 6.895 MPa; I kip= 4.45 kN.

Table 4 Values for Cm S I units1.0

Bottom casting 6.12 [13]For uncoated bars

Top casting 4.71 [10]

Bottom casting 4.08 [8.7]For epoxy-coated bars

Top casting 3.60 [7.6]

I / b

21.28

21.28

21.28

21.28

21.28

21.28

21.28

21.28

24.00

24.00

24.00

24.00

1.4

4.37 [9.3]

3.36 [7.1]

2.91 [6.2]

2.57 [5.5]

Section 12.2.4.1. Also, the applicable factor for epoxy coatingis 1.5 according to Section 12.2.4.3. However, the product ofthe factors for top reinforcement and epoxy coating is takenas 1.7 according to Section 12.2.4.3. f he modification factorfor bar spacing, cover, and transverse reinforcement from Section 12.2.3 is 1.0 or 1.4, the equation for bond stress is u = CmfJ1Idb and values for Cm are shown in Table 4 The upper

limit on u in any case, is 6.41 fJ1 [0.051 .flllwith Jll::;;100 psi [(0.69 MPa)].

The measured bond strength of each beam was divided bythe predicted value using the values of Cm from Table 4 to obtain the bond efficiencies (the measured bond relative to thatobtained using ACI Building Code provisions) listed in Table5. Mean bond efficiency for the uncoated bars is 2.38 with astandard deviation of 0. 71, and mean bond efficiency for theepoxy-coated bars is 2.41 with a standard deviation of 0.49.Current ACI provisions are conservative for all the beams included in Table 5.

Beams with stirrups in the splice region-Eight beamswere tested with ties in the splice region in this research program. Also, beam tests reported by De Vries and Moehle6 included No.3 ( 10-mm) ties in the splice region.

A summary of test data of beams with ties in the splice region is shown in Table 6. The transverse reinforcement parameter K,, is larger than 1.0 for all the beams. Bond ratios(coated to uncoated) vary from 0.71 to 0.99 with an averagevalue of 0.84 and a standard deviation of 0.10. Wide scatterof bond ratios shows that there is no general trend based on

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Measured bond stress

P""'", ukips

/suksi psi Bond ratio

0 18.0 34.8 409 -

0 13.0 25.6 301 0.74

1.02 19.6 37.7 443 -

1.02 15.6 30.5 358 0.81

2.04 21.7 41.6 470 -

2.04 18.0 34.8 393 0.84

1.36 25.5 33.0 388 -

1.36 21.6 28.2 331 0.85

0 20.2 62.2 648 -

0 13.3 41.7 435 0.67

2.13 22.4 68.8 716 -

2.13 16.5 51.1 532 0 .74

concrete strength, bar size, cldb, f sldb, or K values exceeding1.0. A plot of bond ratios versus Krr for beams listed in Table6 and Treece and Jirsa s beams is shown in Fig. 4. Becauseof the wide scatter of the bond ratios, a value of 0.83 (veryclose to the average) seems reasonable for design purposesfor cases when Krr exceeds 1.0. The anchorage length ofepoxy-coated reinforcing bars relative to uncoated bars wouldbe increased by 20 percent when confinement by transversereinforcement exceeds some limiting value.

In Table 6, bond efficiencies relative to Eq. (2) are listedfor each beam. The mean bond efficiency for the uncoatedbars is 2.74 with a standard deviation of 0.41, and the meanbond efficiency for the coated bars is 3.14 with a standard deviation of 0.50. As was the case with beams with no ties inthe splice region, current ACI Building Code provisions arequite conservative for all the beams included in Table 5

Assessment of 1989 ACI Building Code bond provis ionsIn Section 12.1.2 of ACI 318-89, 1 a limit of 100 psi (0.69MPa) is imposed on the value of f.l1. In the Commentary toSection 12.2.2, the ACI Building Code states that research onanchorage capacity of bars in high-strength concretes is notsufficient to allow using a higher value than 100 psi for Jll(0.69 MPa). However, test results listed in Tables 5 and 6show that, for bars in beams with high-strength concrete(above 10 ksi), ACI provisions are more conservative than forlower strength concrete. This implies that the 100 psi limit onthe value of Jll could be increased.

In Section 12.2.3.l(b) of ACI 318-89, a modification factorof 1.0 is applied to basic development length to account forbar spacing, amount of cover, and enclosing transverse reinforcement. The conditions are that cover must not be less thanminimum cover requirements of Section 7. 7.1, and bars mustbe enclosed with transverse reinforcement along the development length with Arr : :dbsN/40. Most beams tested by DeVries and Moehle and listed in Table 6 satisfied transverse reinforcement requirements, but a value of 1.0 could not beused because the cover was 1.125 in. (30 mm), whereas the



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Table 5 Summary of test data for beams with o stirrups in splice region

Casting f/ u Bond*Beam notation Bar type position ksi Bar size c/db f,/db psi ratio Ur/UAC/

BI-11-4-U u Top 3.7 #II 1.42 21.28 409 - 2.82B2-11-4-C c Top 3.7 #II 1.42 21.28 301 0.74 2.71B9-6-4-U3 u Top 3.7 6 0.83 24.00 648 - 2.36BI0-6-4-C3 c Top 3.7 6 0.83 24.00 435 0.67 2.07

Treece and Jirsas0-11-4 u Top 5.0 #II 1.42 25.53 420 - 2.4912-11-4 c Top 5.0 #II 1.42 25.53 280 0.65 2.175-11-4 c Top 5.0 #II 1.42 25.53 300 0.70 2.32

O-ll-4b u Bot. 4.3 #II 1.42 25.53 450 - 2.2212-11-4b c Bot. 4.3 #II 1.42 25.53 240 0.54 1.780-11-8 u Top 8.3 #II 1.42 12.77 790 - 3.6412-11-8 c Top 8.3 #II 1.42 12.77 500 0.63 3.010-11-12 u Top 10.5 #II 1.42 12.77 920 - 3.8612-11-12 c Top 10.5 #II 1.42 12.77 660 0.72 3.620-11-12b u Bot. 9.6 #II 1.42 12.77 840 - 2.7712-ll-12b c Bot. 9.6 #II 1.42 12.77 540 0.64 2.67

Choi et aJ.7

u Bot. 5.4 5Group SPI

c Bot. 5.4 5u Bot. 6.0 6c Bot. 6.0 6

Group SP2u Bot. 6.0 6c Bot. 6.0 6u Bot. 5.9 8

c Bot. 5.9 8Group SP3u Bot. 5.9 8c Bot. 5.9 8u Bot. 5.9 #IIc Bot. 5.9 #II

Group SP4u Bot. 5.9 #IIc Bot. 5.9 #II

u, (Coated) u (Uncoated)I ksi = 6.895 MPa; #II (36 mm); 8 (25 mm); 6 (19 mm); 5 (16 mm).

minimum cover required (Section 7.7.1) is 1.5 in. (38 mm).Based on available test data, it would be more appropriate tochange the limit set on the cover in Section 12.2.3 .l(b) fromthe requirements of Section 7.7.1 to one bar diameter db

Concerning Section 12.2.4.3 of the ACI Building Code, itwas recommended earlier that the 1.2 modification factor alsobe applied to epoxy-coated bars enclosed by ties satisfying Krr;; 1.0, which results in Arr;; dbsN/120. Computed bond efficiencies of epoxy-coated top-cast bars relative to Eq. (2) listedin Tables 5 and 6 indicate that the 1.7 factor recommendedby ACI 318-89 for the combined effect of top casting and

epoxy coating is very high. Top bars included in this researchprogram, in Treece and Jirsa's studys and in DeVries andMoehle 's study,6 had approximately 12.5 to 14.5 in. (32 to 37em) of fresh concrete cast below the bars. This is close to theminimum amount of fresh concrete below the bar [(12 in. (30


1.60 19.20 797 - 1.70

1.60 19.20 592 0.74 1.74

1.33 16.00 675 - 1.49

1.33 16.00 634 0.94 2.11

1.33 16.00 761 - 1.681.33 16.00 577 0.76 1.92

1.50 16.00 627 - 1.86

1.50 16.00 561 0.90 2.49

1.50 16.00 630 - 1.861.50 16.00 538 0.85 2.39

1.42 17.02 552 - 2.33

1.42 17.02 391 0.67 2.48

1.42 17.04 517 - 2.18

1.42 17.02 420 0.67 2.66

em)] set by the ACI Building Code in the definition of a topcast bar. However, tests done at the University of Texas oneffect of casting position on bond strength of reinforcingbars indicated that bars cast with 1 to 6f t (30 to 180 em) offresh concrete below the bars developed more than 80 percent of the bond strength of bottom-cast bars (110.8 = 1.25

Documents

Strength of Epoxy-Coated Reinforcing Bar Splices Confined With Transverse Reinforcement