A Simplified Pushover Method for Evaluating the Seismic Demand in Asymmetric-Plan Multi-Storey Buildings

Buildings with in-plan non symmetric mass and stiffness distributions are characterized by a seismic behavior that is commonly defined as irregular. The reason for such classification is twofold. First, when excited by a lateral ground motion, such buildings instead of simply translating also exhibit torsional behavior. This is basically due to the translational-rotational coupling of the modes. The other reason is that the response of asymmetric-plan buildings usually changes when transitioning from elastic to inelastic behavior. In particular, depending on the elastic properties of the system, on the in-plan distribution of the resisting elements strengths and on the level of the seismic action intensity, the torsional effects may either increase or decrease. Consequently, the seismic demand in such buildings cannot be evaluated through simple conventional analysis procedures, commonly adopted for regular structures. The objective of the present paper is to propose a new pushover method that explicitly takes into account the torsional behavior of asymmetric-plan buildings. The effectiveness of the method is evaluated by comparing the seismic demand of selected case studies with that obtained through both nonlinear dynamic analyses and other pushover methods from literature.