Simple formulas for the estimation of maximum rotational response of one-storey asymmetric systems under seismic excitation

Structures characterized by non coincident centre of mass CM and centre of stiffness CK (Fig. 1), also referred to as asymmetric (or eccentric) structures, develop a coupled lateral-torsional response when subjected to seismic excitation. This coupled behavior may increase significantly the local peak dynamic response of such a structure, as compared to that of an equivalent system with coincident center of mass and center of stiffness (equivalent non-eccentric system). In this paper, starting from a closed-form formulation identified in previous research works by the authors, an estimation of the maximum rotational response of one-storey asymmetric systems under seismic excitation is obtained and developed with respect to different applications. In detail: (1) a corrective eccentricity for the evaluation of the dynamic response of asymmetric systems through “equivalent” static procedures is identified, (2) a sensitivity analysis is carried out upon the accidental eccentricity, (3) the increase in the peak local displacement due to the eccentricity is evaluated at the corner-point of the side of the system. The results provide useful insight into understanding the torsional behavior of asymmetric systems and may directly used for preliminary design and/or check of results obtained through three-dimensional finite-element modeling of the structural system.