Influence of design procedures on the seismic response of bi-eccentric plan-asymmetric systems

This paper investigates, by means of idealized one-storey models, the seismic behaviour of bi-eccentric planasymmetric structures and the influence of different design practices on it. All the examined design procedures are based on the use of modal analysis, in order to grant, in any case, a reliable estimate of the elastic response. The first procedure requires the standard application of modal analysis (nominal positions of mass and stiffness centres), while the others employ a double application of the same analysis to reduce the ductility demand in occurrence of strong ground motions. Furthermore, within the aforementioned procedures, the importance and effectiveness of the combination of design internal forces induced by two orthogonal seismic components are discussed. In order to obtain statistically representative information on the structural response to seismic loads the models are subjected to a set of 30 bidirectional accelerograms. A wide parametric analysis allows observations and conclusions, which may be considered reliable for asymmetric models characterized by a wide range of values of the structural parameters.