Seismic response of irregular multi-storey building structures with flexible inelastic diaphragms

The effectiveness of rigid floor modelling in the seismic design of multi-storey building structures as well as the influence of some structural parameters are deeply investigated through an extensive parametric study. The nonlinear behaviour of 216 structures has been simulated. The basic structural model consists of a symmetrical two-storey system which is supported by seven lateral load-resisting vertical elements with degrading stiffness properties. Different stiffness and strength distributions in the lateral load resisting system and in the floors are considered. The elastic design analysis is carried out by modelling floors as rigid diaphragms or, alternatively, as flexible beams, while the seismic inelastic analyses take into account the real in-plane stiffness and strength of floors. Diagrams show the behaviour of the most important structural element in detail, while statistical techniques are used to identify the most important structural parameters. The results of this study show that the rigid floor hypothesis generally leads to a conservative design for multi-storey buildings, thus confirming the findings of some previous studies on single-storey building structures. Moreover floors need to be adequately designed for strength when they have re-entrances and the stiffness distributions of the lateral-force resisting system is markedly non-uniform