Effects of inplane floor slab flexibility on the seismic behaviour of building structures

Abstract

The rigid floor diaphragm assumption is widely used for the analysis of multistorey building structures because of the simplicity in the analysis procedure. But the application of this assumption to the seismic analysis of building structures may be not valid in many cases. There have been lively discussions about the validity of this assumption. In this study, an efficient analytical model for multistorey building structures including inplane floor slab flexibility without reducing the accuracy of the analysis results is proposed. In addition, a floor flexibility index is proposed for simplified estimation of the inplane floor slab flexibility. The effects of inplane floor slab flexibility are investigated through parametric studies in terms of floor displacements at the roof, seismic base shear, and the distribution of seismic base shear. The effects of the inplane floor slab flexibility on the seismic response are more significant when the aspect ratio of a floor slab system is high or the number of storeys is not great. The inplane floor slab flexibility may bring about a longer vibration period that results in the reduced seismic base shear. However, part of the structure may be subjected to increased stress due to shear force redistribution caused by the large inplane deformation of floor slabs. Therefore, it is desirable to include the inplane deformation of floor slabs in the seismic analysis of building structures for economical and safe design when the inplane deformation of floor slabs is expected to be large.