Maximum seismic rotational response of multi-storey structures

Asymmetric structures develop a lateral-torsional response if subjected to seismic excitation. A careful examination of the equations of motion of linear-elastic single-storey structures has led to the development of a synthetic method (ALPHA method), that, through the use of the so-called ALPHA parameter, allows to estimate the maximum rotational response of the eccentric system as a function of the structural characteristics and the maximum longitudinal displacement of the equivalent non-eccentric system. This method has been effectively applied just to single-storey structures. The objective of this paper is to analyze the torsional behaviour of multistorey structures as subjected to earthquake ground motions and try to extend the validity of theALPHA method to such structures. The results of a wide numerical analysis for the evaluation, for each story of a multi-story structure, of the physical characteristics of a one-story structure, which best estimates the torsional behavior of such structures, is here presented.