Shear friction capacity of monolithic construction joints reinforced with self-prestressing reinforcing steel bars

This study examined the shear friction capacity of a monolithic concrete interface reinforced with newly developed self-prestressed reinforcing steel bars (SPRBs). Twelve push-off specimens with SPRBs were prepared according to the different compressive strengths of concrete (f′_c) by applying compressive stresses (σ_x) on a monolithic concrete interface. To compare the shear friction capacities of monolithic concrete interfaces reinforced with conventional reinforcing bars, four companion specimens were prepared. The test results showed that the shear cracking and shear friction capacities were high for specimens with high f′_c and σ_x values, resulting in the highest values for specimens with f′_c = 40 MPa and σ_x = 0.5f_y, where f_y is the yield strength of the reinforcing steel bar. The test results confirmed that at a similar (ρ_vff_y+σ_x)/f′_c, a σ_x of more than 0.35f_y is required for the SPRBs to achieve a λ_n value comparable to that of the specimens reinforced with conventional reinforcing bars, where ρ_vf is the transverse reinforcement ratio and λ_n is the shear friction capacity. The prediction models ACI 318-19 and AASHTO significantly underestimated the shear friction capacity with low accuracies. In particular, the difference between the experimental and underpredicted values became large as the (ρ_vff_y+σ_x)/f′_c value increased. However, the Mattock's model well-estimated the measured shear friction capacities of all the specimens tested in this study, irrespective of ρ_vff_y and σ_x. Thus, the mean and standard deviation values of the measured-to-predicted shear friction capacity ratio were 1.07 and 0.13, respectively.