Shear Capacity of Cold Joints with Conventional and High-Strength Reinforcement

An experimental program involving 24 reinforced concrete (RC) pushoff specimens was conducted to investigate shear stress transfer across untreated and intentionally roughened cold joints. The variables were the number of bars crossing the joint interface, the reinforcement ratio, the yield strength of the reinforcing steel, and the joint surface roughness. During each experiment, shear and normal stresses across the main crack and joint interface opening and sliding were continuously monitored. The experimental results demonstrate that roughening the joint interface enhances the joint stiffness and peak strength, while the use of Grade 80 steel reinforcement did not result in any strength benefit, although the use of higher-strength steel can improve constructability. The test results were compared with predictions obtained using ACI and AASHTO provisions. Comparison of the measurements and predictions show that both ACI and AASHTO provide generally conservative, yet scattered, estimates of the experimental strengths. Thus, based on the findings of this study, a number of modifications to the current shear friction provisions were proposed to achieve higher strength prediction accuracy.