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78 anchorage at embedment lengths equal to or higher than top and side clear cover to the bar being developed or spliced. AASHTO code development length provision for normal- Details of typical specimens are shown in Table 3.34 and Fig- strength concretes. ure 3.53. In Specimens I-4, I-5, and I-6, transverse reinforce- The effect of admixtures on the transfer and development ment was used in the splice region to confine the concrete as length tests should be studied, with more development shown in Figure 3.54(b). The splice length shown in Column length tests carried out while changing the proportions of 7 of Table 3.34 was selected to provide a direct link with com- different admixtures in the concrete. panion test specimens containing epoxy-coated bars, which were reported on in a separate paper and other tests in the lit- erature. The same splice lengths were used for the specimens 3.8 Experimental Program--Mild with transverse reinforcement so that the confining effect of Steel Anchorage of Uncoated this reinforcement could be evaluated. Rearranging Equation Bars in Tension 12-1 of the 318 Code (ACI 2005) with appropriate modifica- An extensive literature review of test data was conducted, tion factors and with a splice class factor of 1.0, it was possi- and the results were reported in Chapter 2. The findings of ble to estimate a design stress and force in the bars for various the literature review indicated the need to supplement the anchorage conditions, as shown in Equation 3.11. To deter- data with six additional tests of top cast uncoated bar splices mine the calculated stress, fy (specified yield strength of rein- in order to extend the use of the AASHTO LRFD Bridge forcing bars [psi]) is replaced with fs and ld is replaced by the Design Specifications for development and splice length of splice length provided, 16, 24, and 36 in. for specimens with uncoated bars to higher strength concretes. The variables #6 (#19M) bars, specimens with #8 bars, and specimens with considered were bar size (#6, #8, and #11) and amount of #11 bars, respectively. Note that all the specimens had more transverse reinforcement over the splice length. All six speci- than 12 in. of concrete cast below the splice. As shown in mens tested had clear concrete cover of db. Table 3.34, all the bars in the specimens with transverse rein- forcement had a calculated stress over the design stress of 60 ksi. These values are shown in Column 8 of Table 3.34 next to 3.8.1 Specimen Design the yield design value. Six beam splice specimens were tested. The specimen c + K tr dimensions and variables are shown in Table 3.34. The test 40 fc b variables were bar size and the presence of transverse rein- ld db fs = (3.11) forcements in the splice region in higher strength concretes. db 3(1.3) e s The cover value given in Column 3 of Table 3.34 is for both Table 3.34. Specimen dimensions and variables. (1) (2) (3) (4) (5) (6) (7) (8) (9) Specimen Bar Cover Beam Effective Number Splice 318-05 Test Date Size (in.) Size (B x Depth of Spliced Length Cal. Compressive H) (in.) (in.) Bars (in.) Stress Strength (ksi) ( f c , ksi) I-1 #6 0.75 9 x 18 16.88 3 16 52.10 16.2 I-2 #8 1.00 12 x 18 16.50 3 24 44.68 14.6 I-3 #11 1.50 18 x 18 15.75 3 36 49.89 16.2 I-4* #6 0.75 9 x 18 16.88 3 16 60 (66.91) 15.1 I-5* #8 1.00 12 x 18 16.50 3 24 60 (64.54) 14.6 I-6* #11 1.50 18 x 18 15.75 3 36 60 (63.55) 15.1 1 in. = 25.4 mm; 1 ksi = 6.89 MPa. B = specimen width. H= specimen height. (* shows specimens with transverse reinforcement in the splice region)

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79 Splice Region: only I-4, I-5, and I-6 have stirrups in the splice region 18" (12", 9") Ls = 36" (24", 16") 54" 48" 54" #11 Bars: #4@4.5" #4@8" #4@4.5" #8 Bars: #3+#4@8" #4@8" #3+#4@8" #6 Bars: #3@8" #3@8" #3@8" Note. Ls = length of splice. Figure 3.53. Specimen details (1 in. = 25.4 mm). The factor representing the contribution of confining re- ters in both I-5 and I-6. Figure 3.54 shows the specimen rein- inforcement across potential splitting planes is Ktr. The vari- forcing cages. able cb represents the spacing or cover dimension, calculated using either the distance from the center of the bar (or wire) 3.8.2 Test Set-Up to the nearest concrete surface or one-half the distance of the The beam splice setup used in this investigation is shown center-to-center spacing of the bars being developed. e is a in Figure 3.55. In all specimens, the distance between the coating factor of 1.5 for cases with cover less than 3db, or clear loading points and the support was 48 in. The constant mo- spacing less than 6db, and 1.2 for all other cases. The param- ment region was also 48 in. Splices were located within the eter s is a reinforcement size factor: 0.8 for #6 bars and constant moment region. To investigate the characteristics of smaller and 1.0 for all other cases. spliced beams, the applied loads, the resulting deflections at The specimens were checked and reinforced in the over- each beam end and midspan, and strains developed in longi- hang region to prevent premature shear failures outside of the tudinal bars and stirrups were monitored using load cells, lin- test region. To prevent shear failure, a stress of 1.25 times the ear variable differential transducers (LVDTs) anchored to a yield strength of the bar was assumed in the overhang for pur- reference frame, and electrical resistance strain gages attached poses of estimating the required shear reinforcement to resist to the bars, as shown in Figure 3.55 (b) and (c). the maximum shear associated with the moment capacity of the section at the support. The shear reinforcement in the 3.8.3 Materials overhang region consisted of #3 @8 in., #3 + #4 @8 in., and #4 @4.5 in., in Specimens I-1 and I-4, I-2 and I-5, and I-3 and Concrete and reinforcing steel were the materials used. I-6, respectively. The shear reinforcement in the splice region Table 3.35 shows a typical concrete mix for the specimens. consisted of #3 @8 in. on centers in I-4 and #4 @8 in. on cen- This mix was designed for a compressive strength of at least (a) Specimen I-1 (b) Specimens I-4 & I-6 Figure 3.54. Specimen fabrication.

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80 (a) Loading & Supporting (b) Measuring by LVDT G2=15" G1=39" (Plan view for gage location) Ls = 36" 6" 48" 48" 48" 6" (Side view for Supporting) Specimen Bar Size Ls (in.) G1 (in.) G2 (in.) I-1, I-4 #6 (#19M) 16 19 13 I-2, I-5 #8 (#25M) 24 27 9 I-3, I-6 #11 (#35M) 36 39 15 (c) Location of gages and support (Specimen I-3) Note: G1 = Gage 1. G2 = Gage 2. Figure 3.55. Test setup (1 in. 25.4 mm). 15 ksi. The water to cement ratio was 0.20. The average mod- ulus of rupture was 834 psi at 28 days. Typical maximum compressive stress versus age data are shown in Figure 3.56. Table 3.35. Typical concrete mix ratio The concrete strength continued to increase after 28 days and (per 1 cubic yard). achieved a strength of 17 ksi at 56 days. The specimens began to be tested after they reached a 15-ksi uniaxial compressive Contents 15-ksi Mix strength. Cement (lb) 900 The reinforcing bars were ASTM A615 Grade 60 steel and Silica fume (lb) 200 had a yield strength based on tests of samples of the reinforc- Water (lb) 220 ing bars of 78.3 ksi, 70.3 ksi, and 66 ksi for the #6, #8, and #11 Coarse aggregate (lb) 1800 bars, respectively. Stress versus strain curves for #6, #8 and (1/2" crushed limestone) #11 bars are shown in Figure 3.57. Fine aggregate (lb) 1000 High-range water reducer (oz) 520 3.8.4 Cracking and Failure Mode Normal-range water reducer (oz) 38 In nearly all tests, the cracking sequence was similar. First, 1 lb = 0.454 kg; 1 oz = 28.35 gr; 1 yd3 = 0.765 m3; 1 ksi = 6.89 MPa a flexural crack appeared in the constant moment region.

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81 20 18 Compressive Strength (ksi) 16 14 12 10 8 6 4 2 0 0 20 40 60 80 100 Age (days) Figure 3.56. Concrete stress versus age relationship (1 ksi 6.89 MPa). With the increase of beam end loads, a shear crack appeared 3.8.5 Beam End Displacement in the overhang region and was arrested by the presence of the shear reinforcement. Near the peak load, horizontal cracks The applied load versus deflection at the tip of the overhang appeared along the longitudinal bars within the splice region. response for Specimens I-1 to I-6 is shown in Figure 3.59. Finally, the deformations pushed the concrete away from the Load represents the average of the two values from the actua- bar by wedge action. Failure crack patterns of all the speci- tors. Deflections were calculated by averaging displacements mens are shown in Figure 3.58. All the specimens failed in at both ends of the beam. The test results are summarized in splitting mode following yielding of the spliced bars in the Table 3.36. In the specimens without transverse reinforcement constant moment region. in the splice region (Specimens I-1, I-2, and I-3), the end #6 Black Bars 100 90 80 70 Stress (ksi) 60 50 40 30 20 10 0 0 2000 4000 6000 8000 Strain (x10^-6) #8 Black Bars #11 Black Bars 100 100 90 90 80 80 70 70 Stress (ksi) Stress (ksi) 60 60 50 50 40 40 30 30 20 20 10 10 0 0 0 2000 4000 6000 8000 0 2000 4000 6000 8000 Strain (x10^-6) Strain (x10^-6) Figure 3.57. Tensile stress versus strain relationship (1 ksi 6.89 MPa).

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82 (a) Specimen I-1 (b) Specimen I-2 (c) Specimen I-3 (d) Specimen I-4 (e) Specimen I-5 (f) Specimen I-6 Figure 3.58. Failure crack patterns for all the specimens for the #6, #8, and #11 bars.

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83 I-1 I-2 30 50 40 Load (kips) Load (kips) 20 30 20 10 10 0 0 0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 Displ. (in.) Displ. (in.) (a) Specimen I-1 (b) Specimen I-2 I-3 I-4 100 30 90 80 70 20 Load (kips) Load (kips) 60 50 40 10 30 20 10 0 0 0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 Displ. (in.) Displ. (in.) (c) Specimen I-3 (d) Specimen I-4 I-5 I-6 70 100 90 60 80 50 70 Load (kips) Load (kips) 40 60 50 30 40 20 30 20 10 10 0 0 0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 Displ. (in.) Displ. (in.) (e) Specimen I-5 (f) Specimen I-6 Figure 3.59. End load--end displacement curves for Specimens I-1 through I-6 (1 in. 25.4 mm; 1 kip 4.448 kN). displacements at the peak load were 0.5 to 0.7 in. In the spec- constant moment region of Specimen I-6 are shown. Yield imens with transverse reinforcement over the splice region strain in the longitudinal reinforcement was first recorded at (Specimens I-4, I-5, and I-6), the end displacements at the around one-third of the peak load. Table 3.37 shows the peak load were 0.8, 1.6 and 0.8 in., respectively. measured maximum strains on all of the specimens. All the gages on the longitudinal reinforcement showed strains in ex- cess of the bar yield strain before reaching peak load. In the 3.8.6 Bar Strains gages placed on the stirrups in the constant moment region, In Figure 3.60, the typical end concentrated load versus the measured maximum strain was around half of the bar measured longitudinal bar and transverse bar strains in the yield strain in Specimens I-4 and I-5 and almost equal to the

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84 Table 3.36. Summary of test results for uncoated bar specimens. (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) Spec. Max. Displ. 318-05 318-05* AASHTO Test (7)/(4) (7)/(5) (7)/(6) Load at Cal. Cal. Cal. Stress Max. (kips) Peak Stress Stress (ksi) Stress (in) (ksi) (ksi) (ksi) I-1 28.2 0.506 52.10 41.68 38.10 78.55 1.51 1.88 2.06 I-2 39.6 0.429 44.68 44.68 42.86 70.93 1.59 1.59 1.65 I-3 88.6 0.654 49.89 49.89 45.59 67.65 1.36 1.36 1.48 I-4** 29.5 0.805 60 53.54 38.10 81.24 1.21 1.52 2.13 (66.91) I-5** 59.4 1.572 60 60 42.86 91.88 1.42 1.42 2.14 (64.54) (64.54) I-6** 96.4 0.800 60 60 45.59 71.94 1.13 1.13 1.58 (63.55) (63.55) 1 in. = 25.4 mm; 1 kip = 4.448 kN; 1 ksi = 6.89 MPa * Shows stress calculated by removing bar size factor ** Shows specimens with transverse reinforcement in the splice region bar yield strain in Specimen I-6. The use of stirrups in the Jirsa, and Breen study--together with contributions on bond splice region of Specimens I-4, I-5, and I-6 resulted in an in- of reinforcement from ACI Committee 318 and ACI Com- crease in the displacement capacity when compared with mittee 408 that were meant to simplify the provisions for companion specimens I-1, I-2, and I-3, respectively. calculating development length of straight bars in tension-- led to Equation 12-1 in the 318 Code (ACI 2005), which is 3.8.7 U.S. Design Specifications Equation 3.12 herein: 3.8.7.1 318 Code (ACI 2005) 3 f y t e s Orangun, Jirsa, and Breen (1977) evaluated the results of a ld = db (3.12) 40 fc cb + K tr large number of bond and splice tests. The evaluation high- db lighted the importance of parameters such as bar diameter, stress in the bar to be developed ( fc ), cover or bar spacing, In Equation 3.12, fy is the specified yield strength of rein- and the amount of transverse reinforcement. The Orangun, forcing bars (psi), t is the reinforcement location factor of I-6 (longitudinal reinforcement gage) I-6 (transverse reinforcement gage) 100 100 90 90 80 80 70 70 Load (kips) Load (kips) 60 60 50 50 40 40 30 30 20 20 10 10 0 0 0 1000 2000 3000 4000 5000 6000 7000 0 1000 2000 3000 4000 5000 6000 7000 Strain () Strain () (a) Longitudinal gage (b) Transverse gage Figure 3.60. Beam end load versus measured strain relationship in Specimen I-6 (1 kip 4.448 kN).

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85 Table 3.37. Measured maximum strains () in specimens I-1 through I-6. Gage Location I-1 I-2 I-3 I-4 I-5 I-6 Longitudinal Bar 3,405 2,370 3,100 10,300 10,750 5,960 Transverse N/A N/A N/A 1100 875 1,910 Reinforcement 1.3 to reflect the adverse effects on top casting position on the 1963. A brief description of the background of the 1963 ACI bond strength of the reinforcement. The parameter e is a specifications is provided below. coating factor of 1.5 for cases with cover less than 3db, or clear The 1963 edition of the 318 Code provisions for bond and spacing less than 6db, and 1.2 for all other cases. These factors anchorage for ultimate strength design were stated on the are consistent with a ratio of bond strength of coated bars to basis of the ultimate flexural bond stress at the sections of bond strength of uncoated bars observed in the literature of interest (ACI 1963), u 1/1.5 = 0.67 and 1/1.2 = 0.82. However, the product of t and Vu e need not be taken greater than 1.7. The parameter s is a u = (3.13) reinforcement size factor: 0.8 for #6 bars and smaller and 1.0 o jd for all other cases. The factor reflecting the lower tensile Critical sections were stated to occur at the face of support, strength of lightweight concrete is . Bar diameter is db. The at each point of inflection, and at each point where tension factor representing the contribution of confining reinforce- bars were terminated within a span. Vu was the factored shear ment across potential splitting planes is Ktr. The variable cb at the section, o, which represented the sum of bar perime- represents the spacing or cover dimension, calculated using ter(s) at the same section, and jd was the flexural lever arm. either the distance from the center of the bar (or wire) to the To prevent bond failure or splitting, the calculated tension nearest concrete surface or one-half the distance of the cen- or compression force in any bar at any section had to be de- ter-to-center spacing of the bars being developed. The ratio veloped on each side of that section by proper embedment of (cb+ Ktr)/db should not be taken greater than 2.5. length or end anchorage, or, for tension only, by hooks. However, the development length, ld, so calculated, cannot Anchorage, or development bond stress (u), was to be de- be less than 12 in. In addition, when calculating anchorage termined as the bar force, computed from M (moment at the length requirements for tension lap splices, these should be as section due to factored loads) /, divided by the product of required for a Class A or B splice, but not less than 12 in., o times the embedment length. The two values so calcu- where lated--ultimate flexural bond stress and anchorage bond Class A splice..................1.0 ld stress--were not to exceed the limits given below, except that Class B splice..................1.3 ld flexural bond stress did not have to be considered in com- pression or in those cases of tension where anchorage bond It must be noted that this factor is associated with the was less than 0.8 of the permissible stress given below. For potential mode of failure when multiple bars are spliced at tension, there were two equations given for each of the two the same location and does not speak to the actual strength of types of steel included: ASTM A 305 and ASTM A 408. For the spliced bar. instance, for ASTM A 408, the permissible values were the following: 3.8.7.2 2004 AASHTO Specifications (Section 5.11: Development and Splices of Reinforcement) Top bars (more than 12 in. of concrete below the bar)-- 4.2 fc ; The bond provisions for mild reinforcement in the AASHTO LRFD Bridge Design Specifications mirrored the 318 Bars other than top bars--6 f c ; and Code provisions first introduced in the 1963 edition of the For all deformed bars in compression--13 f c or 800 psi. ACI Standard (ACI 1963). At the end of the last decade, the ACI 318 provisions for development and splices of reinforce- In 1971, there was a complete revamping of the bond spec- ment were extensively modified; however, the AASHTO ifications in ACI's 318 Code. In the new format, a basic devel- provisions for development and splices of reinforcement opment length, ldb, was determined and then modified by ap- continued to mirror the ACI provisions first introduced in propriate factors to obtain the required anchorage length, ld.

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86 ld = ldb * f1 * f 2 .... (3.14) which was revised on the basis of a review of available test re- sults on large bars. The revised version for #18 bars was the The development length concept replaced the dual system following: contained in the 1963 ACI Code. It was no longer necessary ldb = 0.125 * f y / fc (3.16) to use the flexural bond concept, which placed an emphasis on the computation of nominal peak bond stresses. The av- with fy and f c in psi. If put in ksi units, erage bond resistance over the full development length of the ldb = 3.95 * f y / fc (3.17) bar is more meaningful in part because of the highly empiri- cal nature of the design provisions and because bond tests in- This is an increase of 12 percent over the values given by volve averaging of bond resistance. The current minimum the current AASHTO LRFD Bridge Design Specifications for development length for bars in tension and in compression is the same size bars. Another important change introduced in based on the attainable average bond stress over this length. the 1989 ACI Code was the limitation that fc cannot be The various ld lengths in the 1971 ACI Code were based di- taken greater than 100 psi. This limitation meant that devel- rectly on the 1963 ACI Code permissible bond stresses. opment lengths would no longer decrease with concrete Slightly modified versions of the 1971 provisions in ACI's 318 strengths greater than 10,000 psi. It was noted that research Code (due to the fact that fy and f c are stated in terms of ksi) on development of bars in high-strength concretes was are the current provisions for these design situations in the not sufficient to substantiate a reduction beyond the limit AASHTO LRFD Bridge Design Specifications. imposed. The basic tension development length, ldb (in.), for #11 bar While these provisions were based on extensive research and smaller bars shall be taken as Equation 3.15: and professional judgment, many found them overly com- plex in application. In 1999, Committee 318 of the ACI re- ldb = 1.25 Abfy/ fc but not less than . . . 0.4 dbfy examined these procedures with the goal of formulating a For #14 bars: ldb = 2.7 fy/ fc more user-friendly format while maintaining general agree- (3.15) For #18 bars: ldb = 3.5 fy/ fc ment with the research results and professional judgment that produced the changed provisions. The revision was and for deformed wire: ldb = 0.95 dbfy/ fc based on the same general equation for development length In Equation 3.15, Ab is the area of bar or wire (in.2), fy is the that served as the basis for the 1989 provisions. This equation specified yield strength of reinforcing bars (ksi), f c is the spec- was Equation 12-1 in the 2005 version of the 318 Code (ACI ified compressive strength at 28 days unless another age is 2005) and Equation 3.11 in this report. specified (ksi), and db is the diameter of bar or wire (in.). In 1977, provisions for tension lap splices of deformed bars The tension development length, ld, shall not be less than and deformed wire encouraged the location of splices away the product of the basic tension development length, ldb, and from regions of high tensile stresses to locations where the modification factor specified in Article 5.11.2.1.2 (for epoxy- area of steel provided at the splice location is at least twice that coated bars with cover less than 3db or with clear spacing be- required by analysis. A lap splice of any portion of the total tween bars less than 6db . . . 1.5, For epoxy-coated bars not area of steel in regions where (As provided/As required) was covered above . . . 1.2 ). The tension development length shall less than 2.0 had to be at least 1.3 times the development not be less than 12.0 in., except for lap splices specified in length of the individual bar in tension (Class B splice) in Article 5.11.5.3.1 (Class A splice . . . 1.0 ld, Class B splice . . . length. If more than one-half of the reinforcement was 1.3 ld, Class C splice . . . 1.7 ld). spliced in such regions, lap splices had to be at least 1.7 times In the 1989 ACI Code, major changes were made in the the development length of the individual bar (Class C splice) procedures for calculating development lengths for deformed in length. Class A splices where the length of bar was equal to bars and deformed wire in tension. This represented a major the development length of the individual bar were only per- departure in approach between the ACI Code and the current mitted in regions where (As provided/As required) was less AASHTO LRFD Bridge Design Specifications. These changes than 2.0 and no more than 25 percent of the total area was resulted in an increase in the development lengths for closely spliced within one lap length. These same provisions are in spaced bars and bars with small covers. The basic develop- the current AASHTO LRFD Bridge Design Specifications. ment length was modified to reflect the influence of cover, When the changes in development in tension that eliminated spacing, transverse reinforcement, casting position, type of many concerns regarding tension splice due to closely spaced aggregate, and epoxy coating. The basic development lengths bars were introduced in the 1989 version of the 318 Code remained essentially the same as in the 1971 edition of the (ACI 1989), Class C splices were eliminated. ACI Code and the current AASHTO LRFD Bridge Design In summary, there are a few major differences between the Specifications with the exception of the equation for #18 bars, ACI Code and the AASHTO LRFD Bridge Design Specifica-

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87 tions with respect to development and splice length of tension specimens with bottom bars (478 specimens) was 0.51 to reinforcement: 3.02, and some specimens had a ratio of less than 1, which means the test bond strength was lower than the strength cal- The AASHTO LRFD Bridge Design Specifications don't culated using the 318 Code (ACI 2005) without bar size have bar size factor for smaller bars. factor. The bond strength of specimens with top bars (111 The AASHTO LRFD Bridge Design Specifications don't specimens) was 1.04 to 3.27. In tests for this study, the ratio consider the role of confining reinforcement over the splice of test result to calculated result was 1.13 to 1.88. The design region; however, in the ACI Code, the Ktr factor represents equation without the bar size factor conservatively estimated the contribution of confining reinforcement across poten- bar stress for the specimens with top bars. However, it over- tial splitting planes in the case of closely spaced bars with estimated the bar stress in many specimens with bottom bars, small covers. especially for specimens with concrete compressive strength The AASHTO LRFD Bridge Design Specifications still con- higher than 10 ksi. These are tests with values greater than 100 tain Class C splices. The second and third differences are, psi along the horizontal axis. Figure 3.61(d) shows the com- of course, related. This parameter is especially important parison of test maximum stress to calculated stress in the bar because bars are being developed in higher strength using Equation 3.15 (AASHTO LRFD Bridge Design Specifi- concretes. cations) on uncoated bars for the specimens reported by ACI Committee 408 (2003). The bond efficiency (the ratio of test stress to calculated stress using AASHTO LRFD Bridge Design 3.8.8 Bond Strength Comparisons Specifications) of specimens with bottom bars (478 speci- Table 3.36 shows the comparison of calculated stress in the mens) was 0.50 to 2.63, and 85 specimens had less than 1, bar using Equations 3.12 and 3.15 and test results. In the spec- which means the test bond strength was lower than the imens with transverse reinforcement (Specimens I-4 through strength calculated by Equation 3.15. I-6), the 318 Code (ACI 2005) calculated stress was higher ACI Committee 408 (ACI 408R-03) proposed a new design than the calculated stress in specimens without transverse re- equation for the bond and development of straight reinforc- inforcement (Specimens I-1 to I-3). Also, the use of transverse ing bars in tension based on research by Zuo and Darwin reinforcement over the splice region increased deflection at (2000). Figure 3.61(e) shows the comparison of stress in the failure. The ratio of test maximum stress to ACI-calculated bar calculated using Equation 3.18 and the previous test stress in the bar ranged from 1.13 to 1.59. The ratio of test results reported by ACI Committee 408 (2003). The result maximum stress to AASHTO-calculated stress in the bar shows that the ratio of bond efficiency of specimens with bot- ranged from 1.48 to 2.14. It should be noted that the second tom bars was 0.79 to 2.26, and only 12 specimens showed a part of Equation 3.15 controlled the basic development length ratio of less than 1. in the entire specimen, and the calculated flexural capacity was fy greater than the moment at failure. The failure moment - 2200 fc1/4 ranged between 60 and 98 percent of the flexural capacity. ld = db (3.18) Column 5 in Table 3.36 shows the calculated stress with the 70 c + K tr db bar size factor removed. Even though the test results of NCHRP Project 12-60 do not result in ratios of test maxi- In Equation 3.18, is a factor reflecting the lower tensile mum stress to calculated stress less than 1.0, on the basis of strength of lightweight concrete, is 1.2 for all epoxy-coated the analysis of the entire database, it is proposed that the 0.8 bars, is a factor reflecting the lower tensile strength of light- bar size factor not be used for smaller bars. In Figure 3.61(a), weight concrete, and c, , and Ktr are defined as follows: the comparison of test maximum stress to the stress calcu- c = cmin + 0.5db (3.19) lated using 318 Code (ACI 2005) for uncoated bottom bars (reported by ACI Committee 408 [2003] and discussed in where Chapter 2) is shown. It can be seen that many of the speci- c = spacing or cover dimension mens had ratios less than 1. = cmin + db/2; Figure 3.61(b) and (c) show the comparison of test maxi- cmin = minimum concrete cover or one-half of the clear mum stress to calculated stress in the bar using Equation 3.11 spacing between bars, whichever is smaller, without bar size factor for test results on uncoated bars = minimum (cb, cs); reported by ACI Committee 408 (2003). In these figures, the cb = bottom concrete cover for reinforcing bar being de- specimens are divided by casting position. The bond veloped or spliced; efficiency (the ratio of test maximum stress to stress calcu- cs = minimum [cso , csi + 0.25 in.]; lated using 318 Code [ACI 2005] without bar size factor) of cso = side concrete cover for reinforcing bar;

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88 3 2.5 Bond Efficiency (Test/ACI-05) 2 1.5 1 0.5 0 0 20 40 60 80 100 120 140 Concrete Strength (fc', psi) (a) Specimens with Bottom Bars (ACI-05) 3.5 3.5 3 3 Bond Efficiency (Test/ACI-05*) Bond Efficiency (Test/ACI-05*) 2.5 2.5 2 2 1.5 1.5 1 1 0.5 0.5 0 0 0 20 40 60 80 100 120 140 0 20 40 60 80 100 120 140 Concrete Strength (fc', psi) Concrete Strength (fc', psi) (b) Specimens with Top Bars (ACI-05*) (c) Specimens with Bottom Bars (ACI-05*) 2.5 3 2.5 2 Bond Efficiency (Test/ACI-408) Bond Efficiency (Test/AASHTO) 2 1.5 1.5 1 1 0.5 0.5 0 0 0 20 40 60 80 100 120 140 0 20 40 60 80 100 120 140 Concrete Strength (fc', psi) Concrete Strength (fc', psi) (d) Specimens with Bottom Bars (AASHTO) (e) Specimens with Bottom Bars (ACI-408) (*shows stress calculated by removing bar size factor, 1 psi = 6.89 kPa) Figure 3.61. Comparison of bond efficiency with concrete strength.