Vertical Punching Capacity of Reinforced Concrete Flat Plates without Shear Reinforcement

Reinforced concrete flat-plate systems are widely adopted in buildings owing to ease of construction and facilitating larger clear story heights. Flat plates are routinely designed for two-way shear to preclude brittle punching failures. Accurate assessment of concrete contribution to shear strength is particularly important for flat plates in carrying out a reliable and economical design. To address this, an efficient analytical method based on the softened strut-and-tie model to estimate punching capacity of flat plates without shear reinforcement under gravity loading is presented. The proposed method can account for the influence of various key parameters such as concrete strength, plate thickness, column geometry, longitudinal reinforcement area, and arrangement of tension reinforcement. The proposed method, when verified against data from 224 specimens reported in the literature, showed reasonably good accuracy with a mean test-to-estimated capacity ratio of 1.20 and a coefficient of variation (CoV) of 0.19. In comparison, average capacity ratios using ACI 318-19 and Eurocode 2 provisions were 1.60 and 1.27 (CoV of 0.34 and 0.29), respectively. A comprehensive discussion on the effects of key parameters on punching behavior of flat plates without shear reinforcement is presented, and suggestions to improve existing design provisions are provided.