Non-linear finite element analysis of reinforced concrete flat plates with opening adjacent to column under eccentric punching loads

Abstract

Nonlinear finite element analyses were performed on interior slab-column connections to investigate the effects on the punching strength of flat slabs. A total of twenty-seven three-dimensional finite element models were constructed to represent large-scale flat plate slabs (2000 × 2000 × 155 mm) subjected to concentric and eccentric punching loads. The main parameters in this study were the eccentricity of the load, the opening size, the location of the opening relative to the direction of the transfer moment, and the configuration of the reinforcement adjacent to the opening that is used to compensate the cutting bars. The dimensions and reinforcement of the slab and column were kept constant. Predictions of the numerical models were in good agreement with experimental results published in the literature for slab column connections subjected to concentric loading. The numerical investigation showed that the presence of an opening adjacent to a column in a specimen subject to concentric loads could cause a significant reduction in the ultimate shear capacity which increases with the increase in the size of the opening. Specimens with 250 × 250-mm size openings indicated a reduction of 35% in their ultimate shear strength capacity while specimens with 250 × 450-mm size openings indicated a reduction of 45%. Specimens without openings subjected to load eccentricities of 112.5 and 225 mm resulted in a reduction in the load capacity of 18 and 28%, respectively. It was found that providing continuous bars adjacent to the opening to compensate the cutting areas of reinforcement could result in a considerable improvement in the serviceability of the slab represented by an increase the stiffness of the slab-column connection and no significant effect on the punching capacity for the case of concentric loads. Finite element analyses performed are in good agreement with provisions in the building code (e.g., ACI-318) for the case when the opening is located parallel to the direction of the principal moment and provide conservative values when the opening is in the upward side of the bending moment. Keywords: Reinforced concrete plats, Punching shear resistance, Opening, Nonlinear finite element, Eccentric load