| This study investigates the in-plane seismic characteristics of reinforced concrete floor slabs which function as diaphragms placed between lateral load resisting systems. The paper focuses on the floor slab system with edge beams, referred to as the beam-supported floor system. The investigation consists of four phases: (1)experimental study, (2) analytical study, (3)parametric study, and (4)dynamic response analysis.; In the experimental study, scaled models (a scale ratio of 1:4.5) representing a portion of the floor system in a building structure were tested under various loading and support conditons. The experimental findings indicate that the development of a crack extending along the boundary between the column and middle strips controls the ultimate in-plane strength of the test panels, while the opening and closing of the crack primarily controls the behavior of the panels in post-ultimate load regions. It was found that cyclic loading or the application of the vertical load can reduce the ultimate in-plane strength by as much as 20 to 25 percent.; A non-linear finite element model was developed for the purpose of the analytical study. The model successfully predicts the ultimate strength of the test slab panels subjected to monotonic in-plane loading and duplicates the experimental load-deflection curves. The model also reproduces the unloading stiffness of the test slab panels.; The effects of geometry, reinforcement, loading, and support conditions on the in-plane characteristics of floor slabs were investigated in the parametric study. General and practical procedures were developed to evaluate the in-plane strength and stiffness of floor slabs. The in-plane flexural strength of floor slabs can be computed by treating them as deep beams considering both flexural and shear deformations. A reduction factor is incorporated into the deep beam calculation in order to represent the stiffness degradation in the post-elastic range.; In the dynamic response analysis, a seven story and six bay symmetrical building model was selected in order to examine the influence of in-plane characteristics of floor slabs on the building response. Compared with the analysis based on the usual rigid slab assumption, the incorporation of elastic in-plane deformation of the floor slabs resulted in a 300 percent increase in the base shear applied to flexible vertical members. The base shear resisted by the flexible vertical members was increased further by 100 percent when the non-linear behavior of floor slabs and vertical members were considered. |
