Modification of KDS 14 Design Model for Punching Shear Strength of Slab-Column Connections Reinforced with Various Types of FRP Rebars

The current Korean Standard KDS 14 has adopted a strain-based shear strength model for evaluating the punching shear strength of slab-column connections reinforced with steel rebars. Thus, this study evaluated the applicability of the KDS 14 design model for slab-column connections reinforced with FRP rebars. The KDS 14 model was improved by modifying the equation for determining the depth of the compression zone, taking into account the material characteristics of FRP reinforcement. The modified KDS 14 model was evaluated by conducting a comparative analysis with existing design codes over a comprehensive database of 150 interior FRP-reinforced interior slab-column specimens with and without shear reinforcement. The results indicated that the modified KDS 14 model provided promising performance over various design parameters by exhibiting a similar scatter and conservatism compared to the JSCE 2007 and CSA codes with a COV of approximately 15%, while showing better correlation with the dataset than most existing design codes. In addition, a parametric analysis was conducted to investigate the primary design parameters that affected the punching shear stress capacity at the critical section of FRP-reinforced slab-column connections using both the modified KDS 14 model and existing design codes. Overall, all prediction models exhibited similar trends. Further, they were consistent with the experimental results according to variations in design parameters, including concrete compressive strength, slab effective depth, FRP axial stiffness, and column dimension.