The assumption of rigid floor diaphragm is valid in most cases of simplified analyses of building structures. However, there are situations where the floor diaphragms can not be considered as rigid. The in-plane floor flexibility is particularly significant for buildings with a high aspect ratio of floors, with stiff end walls and with plans in the shape of the letters L, T, V, etc. Thus, the flexibility of floors is significant in the analysis of this type of building structures.
An efficient model for three-dimensional analysis of multistory building structures with flexible floor diaphragms is proposed in this paper. Three-dimensional analysis of a building structure using a finite element model requires tedious input data preparation, longer computation time, and larger computer memory. The model proposed in this study is developed by assembling a series of two-dimensional resisting systems and is considered to overcome the shortcomings of a three-dimensional finite element model without deteriorating the accuracy of analysis results. Static and dynamic analysis results obtained using the proposed model are in excellent agreement to those obtained using three-dimensional finite element models in terms of displacements, frequencies, and mode shapes. Effects of flexibility of floor diaphragm on seismic response of multistory building structures are investigated.