Effect of gravity shear ratio on governing failure mode of reinforced concrete slab-column connections

Abstract

Abstract Reinforced concrete (RC) flat slabs are widely being applied to almost every building structure due to their distinct advantages. Nevertheless, there has not yet been a definitive method to precisely foresee the governing slab failure modes. This research was targeted at predicting the main failure mode of RC slab-column connections subjected to unbalanced moment and various vertical shear forces, for the first time. Thus, the failure modes of the connections were deviated by comparing the unbalanced moment capacity at punching shear failure controlled by the codes and unbalanced moment strength at the flexural mechanism checked by the yield line theory (YLT). The procedure was validated by the results of experimental tests carried out at authentic research in the literature. Afterward, 200 case studies were done on the connections under moment transfer at 20%, 40%, and 60% of gravity shear ratios (GSRs), regarding the alteration of flexural reinforcement ratio from zero to 3.0%. Openings and shear strengthening were looked into in the case studies as two highly effective parameters for the governing failure mode. The intersection of unbalanced moment capacities owing to punching shear and flexural collapses with respect to the longitudinal reinforcement ratio indicated the coordinate of boundary point (BP) between possible failure modes. It was proved that the GSR rise and the existence of opening, lead to a decline in the coordinate of BP notwithstanding, the effect of shear strengthening was in reverse.