Lateral stiffness of reinforced concrete interior flat plate connections

•The use of grillage analysis to predict the nonlinear seismic behaviour of flat plates was validated.•The effective slab width required to calculate the lateral stiffness of a flat plate system was examined.•Expressions to estimate the nominal and factored effective slab width were proposed.•The effective slab width was found to increase with the increase of flat plate span.•The ratio of Beff to B was found to decrease with the increase of bay width.

Flat plates are widely used in reinforced concrete structures. To evaluate the lateral stiffness of a flat plate system, the contributing slab width needs to be defined. In this paper, a model that utilizes grillage analysis is proposed to predict the nonlinear lateral behaviour of flat plate structures. The model is then utilized to conduct a parametric study to evaluate the effective slab width contributing to the lateral stiffness of residential interior flat plate connections. The studied parameters are span length, bay width, column dimensions, and level of column axial load. Both gravity load designed frames and moment resisting frames are analysed. The effect of the material safety factors is assessed by conducting two sets of analyses using nominal material properties and factored material properties. Equations for estimating the effective slab width contributing to the lateral stiffness of the system are proposed.

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