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55 the use of smaller aggregate (see Appendix A) and its effect on mechanical bond. 4. Slip at 125 ksi is unaffected by the development length pro- vided. Hence, there is reserve bond capacity beyond that implicitly assumed by the development length calculation. 5. The specimens having confining steel exhibited marginally (<0.02 in.) greater slip at 125 ksi than those that did not. This observation is counterintuitive although the difference is small and may be attributed to experimental scatter. The hook test series was intended as proof tests of the pres- ent AASHTO hook development requirements given by Equa- tion 14. These tests have shown that the present requirement is (a) Slip at Different Stress Levels adequate to develop up to 125 ksi in 10 ksi concrete in cases where adequate cover and confinement--based on current design requirements--are provided. 2.8.3 Summary and Conclusions The objective of this portion of the study was to evaluate existing AASHTO requirements in reference to the use of high-strength reinforcement (represented by ASTM A1035) with respect to issues of bar splice development and hooked bar anchorages. Spliced beam straight bar development tests and hooked anchorage pullout tests were performed as proof tests of the current AASHTO requirements as expressed by Equations 12 and 14. The small number of splice beam tests conducted augmented the extensive study by Seliem et al. (b) Slip at 125 ksi (2009) and extended the available database to higher strength Figure 36. Slip of embedded hooks. concrete. The results demonstrate that the present AASHTO require- ments for both straight bar tension development and hooked anchorage tension development may be extended to develop Figure 36b shows only the slip values reported at 125 ksi sorted bar stresses of at least 125 ksi for concrete strengths up to 10 ksi against (1) concrete strength (5 or 10 ksi); (2) design bar stress provided adequate cover and confinement are provided. (100 or 125 ksi); and (3) the presence of confining reinforce- In using higher strength steel, greater bar strain and slip ment (N specimens had no confining reinforcement). will occur prior to development of the bar. The associated Conclusions drawn from Figures 35 and 36 include the displacement of the bar lugs drives a longitudinal splitting following: failure beyond that where yield of conventional bars would occur; thus, confining reinforcement is critical in developing 1. Through the proof loads (100 and 125 ksi), slip is limited higher strength bars. The results of this study and previous and rarely exceeds 0.06 in. Indeed, through stresses of work clearly indicate that confining reinforcement, designed 140 ksi, slip rarely exceeds 0.09 in. and is not affected by in a manner consistent with current practice, should always bar size, concrete strength, development length, or the pres- be used when developing, splicing, or anchoring ASTM A1035 ence of confining reinforcement. or other high-strength reinforcing steel. 2. Slip is not significant until near the ultimate load (greater than 140 ksi). It is noted that in some cases, the large values 2.9 Serviceability Considerations of slip include the plastic deformation of the reinforcing bar in the gage length over which slip is measured. A fundamental issue in using A1035 or any other high- 3. Slip at 125 ksi is marginally (<0.01 in.) more pronounced strength reinforcing steel is that the stress at service load ( fs; for the 10 ksi concrete. This slight increase is attributed to assumed to be on the order of 0.6fy) is expected to be greater