Mass eccentricity effects on the torsional response of inelastic buildings – a case study

In this paper, the effects of accidental mass eccentricities on the inelastic rotational behaviour of multi-storey buildings subjected to unidirectional seismic excitations are studied. Design codes require the specification of structural detailing to preserve the post-elastic deformation capacity of building structures. Most of these code provisions are based on studies of planar structures, and it is recommended that any mass eccentricity be taken into account by performing three-dimensional static or dynamic analyses, which involve shifting the centres of the floor masses from their nominal positions to what is called an accidental eccentricity. This paper addresses the issue of accidental mass eccentricities on the torsional response of asymmetric multi-storey buildings, which are displaced beyond their elastic limit. It complements a recent study which investigates this issue in the linear phase of deformation and demonstrates that the effects of any height-wise variation of accidental eccentricities are not significantly different in the elastic and inelastic state of deformation, provided that (a) the structural configuration is designed to provide a predominantly translational response in the elastic state, and (b) the strength assigned to each lateral load-resisting element has been derived from a planar static analysis under a lateral loading simulating a translational mode of vibration.