Effect of High-Strength Reinforcement Steel on Shear Friction Behavior

Current bridge provisions limit the contribution of the reinforcing steel in concrete shear interface design to a yield strength of 420 MPa (60 ksi). Because of this, the higher yield strength of high-strength steel (HSS) reinforcing bars cannot currently be used in design. Only a limited number of tests have been performed to characterize the shear friction resistance of members containing HSS, and results from these tests indicate that using the full HSS reinforcing bar yield stress capacity could overestimate the shear interface capacity of the specimens. However, shear friction design using HSS reinforcement at its yield strength, if shown viable, could provide constructability benefits. In this work, the effect of HSS reinforcement on concrete–concrete shear interface capacity is investigated. The specimens had varying reinforcing steel ratios (0.42 and 0.64%), bar sizes [#13M (#4) and #16M (#5)], and steel grades [Grade 420 (60 ksi) and Grade 550 (80 ksi)]. Four sets of five push-off test specimen types were tested for a total of 20 specimens. All push-off specimens were designed to have similar interface shear resistance using current design equations. Testing results indicate that although the peak strength capacity of the specimens reinforced with Grade 550 #16M (#5) bars was greater than that of the Grade 420 #16M (#5) bars, a similar increase was not observed in the #13M (#4) specimens in which negligible differences were observed in the peak strength. However, the use of HSS reinforcement increased the postpeak sustained loads.