Equivalent SDOF systems for the estimation of seismic response of multistory frame structures

Abstract

In this research an approximate investigation has been carried out on the seismic response of multistory frame structures. The simplifying hypothesis on which the adopted methodology is based is the assumption of an assigned time-independent global deflection shape for the lateral displacements of the frame. This hypothesis corresponds to consider the dynamic response of the frame limited to the first vibration mode only, both in elastic and in inelastic behavior. The above mentioned simplification firstly allows the reduction of the response of MDOF systems to the response of an equivalent simple system (ESDOF), defined by means of appropriate values for mass, stiffness and viscous damping; on the other hand, it allows an approximate extension of the calculation of parameters characterizing the seismic response, easily obtainable for SDOF systems, to multistory frame systems. The analyses have been concerned different aspects of seismic response: strength, displacement, input energy and dissipated energy demands have been evaluated. The study has been extended to some damage indexes: although these parameters still do not have an exact and complete definition. The simplifying choice of using an assigned modal shape also for the inelastic response, although affected by the approximations implicitly present in this formulation, offers the possibility to investigate the influence of the adopted global deflection shape on response parameters; the importance of this aspect is in the fact that the shapes can correspond to different stiffness and strength distribution along the height of the building.