Parametric analysis of reinforced concrete slabs subjected to earthquake excitation
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Reinforced concrete slabs in the building industry can be used as wall panels roof slabs and floor slabs. A slab is subjected to the horizontal component of an earthquake excitation when it is used as a wall panel and to the vertical component, when it is used as a roof or floor slab. In this study, floor slabs are analyzed under vertical earthquake excitation. The purpose of this study is to determine the effects of various parameters such as the aspect and flexural rigidity ratios and the boundary conditions on the linear response of representative concrete floor slabs with rigid boundary members to vertical earthquake excitation. A computer program is developed to analyze the dynamic out-of-plane response. The finite difference method is used for spatial integration and Newmark's-â method is used for time integration. The differential equations of motion of a rectangular orthotropic slab are first derived using thick plate theory. Then the finite difference formulation of the problem is presented for thick slabs subjected to uniformly distributed static loads. Next the corresponding formulations are presented for thin slabs subjected to uniformly distributed static loads and to an earthquake excitation. Flexural rigidities of reinforced concrete slabs are calculated. An earthquake accelerogram is generated using a nonstationary stochastic model. The first six natural frequencies and mode shapes of slabs with simply supported and clamped boundary conditions are examined for different flexural rigidity and aspect ratios. The maximum displacements and internal forces of slabs subjected to a uniformly distributed static load and to the vertical component of an earthquake excitation are studied for different flexural rigidity and aspect ratios, and limiting values of these parameters are discussed for both boundary conditions considered. It is concluded that the aspect ratio of the slab has a stronger influence on all responses than the flexural rigidity ratio. Graphs and tables are presented that should help engineers in the design of reinforced concrete floor slabs for combined static and earthquake loading.