Nonlinear analysis of flat post‐tensioned concrete slab–edge column connections

Abstract This study presents nonlinear finite element analyses to investigate the punching shear behavior of unbonded post‐tensioned concrete flat slabs at slab‐edge column connections. A parametric analysis was conducted to evaluate the influence of four critical parameters on the punching shear resistance: the distribution of prestressing tendons, the presence of unbalanced moments parallel to the free edge, the flexural reinforcement ratio, and the concrete compressive strength. The numerical models were calibrated and validated against experimental data, demonstrating satisfactory accuracy in reproducing load–displacement behavior and failure mechanisms. The analysis revealed that the distribution of prestressing tendons significantly affects punching shear capacity. Configurations with tendons concentrated perpendicular to the free edge exhibited a notable increase in ultimate load and a transition from punching shear to a flexural‐punching failure mode characterized by ductile behavior. The presence of unbalanced moments parallel to the free edge resulted in a reduction of approximately 20% in punching shear resistance, accompanied by non‐symmetric slab rotation, stress concentrations, and increased cracking on one side of the slab. Parametric studies further showed that increasing the reinforcement ratio enhances punching shear capacity by about 30%, while higher concrete compressive strength contributes an increase of approximately 15%. The reinforcement ratio was found to exert a greater influence on punching resistance than concrete strength. Comparative analysis with design codes—NBR 6118:2023, fib Model Code 2020, ACI 318‐19, and the final draft of Eurocode 2—indicated that most codes provide conservative estimates, particularly under unbalanced moment conditions. This conservatism stems from tendon force increments due to slab deflection and the empirical safety factors used to penalize the effects of unbalanced moments. Overall, the study highlights the importance of accurately modeling prestressing tendon distribution and unbalanced moments to predict punching shear behavior, emphasizing the need for improved design provisions to reduce conservative biases in code‐based predictions.