Behavior and Modeling of Reinforced Concrete Slab-Column Connections

Experimental results of five large-scale isolated slab-column connections subjected to three types of loading histories are presented. The subassemblies represented typical flat-plate construction designed prior to the 1980’s that had low slab reinforcement ratios and discontinuous bottom reinforcement at the column. The specimens failed in punching after extensive slab flexural yielding occurred. The damage induced by simulated seismic loading to a prescribed drift level (1.25%) did not reduce the connection punching capacity under gravity loading. The post-earthquake connection stiffness was significantly reduced. The flexural reinforcement ratio had a significant effect on connection strength and stiffness.

Test data for interior flat-plate slab-column connections subjected to concentric gravity load and combined gravity and lateral loads were collected. The connection strength was evaluated using ACI code design equations. From test data, equations for connection gravity load capacity as a function of concrete strength, slab reinforcement ratio and yield strength, and the ratio of column size to slab effective depth were developed.

Based on a beam analogy concept, a 2D nonlinear model for interior slab-column connections was developed for use in pushover analyses of flat-plate structures. The slab lateral resistance from flexure and shear acting on the connection was modeled by an equivalent beam element and the resistance from torsion by a rotational spring element. The parameters defining connection lateral stiffness were calibrated from the tests presented in this study and were validated using experimental data reported in other studies.