Nonlinear Finite Element Analysis of Reinforced Concrete Flat Slabs Subjected to Reversed-Cyclic Loading

Abstract

Flat slabs are only permitted to be used as gravity-load carrying systems in regions of high seismicity because of poor resistance to lateral deformation and punching shear under reversed cyclic loading. This paper considers the influence of reverse cyclic loading on the punching resistance of internal slab column connections without shear reinforcement. Currently, ACI 318-14 determines the deformation capacity of slab-column connections using a best-fit line based on test data from relatively thin slabs, with average thickness of 110 mm, and flexural reinforcement ratios of around 1%. Consequently, the ACI 318-14 (2014) design recommendations require further validation for slab thicknesses and reinforcement ratios outside this range. A possible tool for doing this is the mechanically-based critical shear crack theory (CSCT) of Muttoni (2008). The model is based on considerations of equilibrium and kinematics for an isolated axis-symmetrical slab. The model gives good predictions of punching resistance under concentric loading but its applicability to the design of flat slabs subject to reversed-cyclic loading requires further consideration. The paper presents the results of a parametric study which was carried out with the finite element program ATENA (Cervenka et al. 2007) in order to obtain an improved understanding of the influence of cyclic degradation on punching resistance. Maximum slab rotations are shown to increase under cyclic loading with a consequent degradation in unbalanced moment resistance and ultimate slab rotation. This finding is consistent with the predictions of the CSCT.