Stiffness reduction for flat plate systems due to cracking

Abstract

The purpose of this study is to propose a stiffness reduction factor for flat plate systems under lateral loads. According to current design provisions, slab stiffness under lateral loads should account for stiffness reduction due to the effects of cracks. Several researchers have conducted for evaluating the stiffness reduction in flat plate slab systems under lateral loads. However, no research is found for establishing strength reduction factor with respect to the level of applied moment. This study attempted to propose equations for calculating stiffness reduction factor with respect to the level of applied moment (Ma) represented by the ratio of Ma to the cracking moment of the slab (Mcr). For this purpose, test results of 20 interior slab-column connections were collected. For each specimen, stiffness reduction was measured with respect to Ma/Mcr. To verify the proposed factor, this study conducted the experimental test of interior connection under quasi-static cyclic loading, from which load-deformation curve was obtained. The curve was compared with that obtained from the effective beam width method with the proposed stiffness reduction factor. It shows that the proposed factor accurately predicts stiffness reduction in flat plate systems.