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

The shear friction capacity (SFC) of a monolithic concrete interface reinforced with newly developed self-prestressing reinforcing steel bars (SPRBs) was examined. A total of 12 SPRB-reinforced push-off specimens with different concrete compressive strengths (f′ c ) were prepared and different compressive stresses (σ x ) were applied to the monolithic concrete interface. To compare the SFCs of monolithic concrete interfaces reinforced with conventional reinforcing bars, four companion specimens were prepared. The test results showed that the shear cracking and SFCs were high for specimens with high f′ c and σ x values, with highest values for specimens with f′ c = 40 MPa and σ x = 0.5f y (f y is the yield strength of the reinforcing steel bar). The test results confirmed that, at a similar reinforcement index ((ρ vf f y + σ x )/f′ c ) (ρ vf is the transverse reinforcement ratio), σ x > 0.35f y is required for the SPRBs to achieve a SFC (λ n ) comparable to that of specimens reinforced with conventional reinforcing bars. Code prediction models were found to underestimate the SFC significantly. In addition, the difference between the experimental and predicted values increased with an increase in (ρ vf f y + σ x )/f′ c . However, Mattock's model produced good estimates of the measured SFCs of all the specimens tested in this study, irrespective of the values of ρ vf f y and σ x . The mean and standard deviation of the measured-to-predicted SFC ratio were 1.07 and 0.13, respectively.