In‐Plane Floor Deformations in RC Structures

The assumption of in‐plane floor rigidity, commonly used in the analysis of reinforced concrete multistory buildings subjected to lateral loads, is examined by analytically investigating 37 buildings. These are chosen to cover parameters including: number of stories, story height, slab type, building‐plan aspect ratio, regularity of building plan, openings in the slab, and the sizes and spacing of columns and shear walls. A three‐dimensional finite element model is constructed for each building, and two analyses are conducted. The first incorporates all the in‐plane degrees of freedom, while the second is based on three rigid‐body displacements per floor. Error resulting in the latter solution is assessed as the given parameters are varied. The criteria for comparison are primarily the lateral deflection, column and wall shear, and interstory shear. A simple empirical error bound on the shear is suggested. This error bound is expressed in terms of an in‐plane rigidity factor, which gives a measure of the ratio of in‐plane stiffness of the slab to lateral stiffness of the building.