Evaluation of the inelastic demand of structures subjected to multiple ground motions

Abstract

In the current seismic design format, the key issue in establishing realistic seismic loads is the behavior factor. It accounts for all the dissipative mechanisms that a structural system may develop under a strong ground motion, however not clearly enough stated yet. It corresponds to the performance level associated to the ultimate limit state (i.e. life safety), related to a 100 years mean return interval of earthquake ground motion with a prescribed peak acceleration of ground.
The paper investigates the effect of repeated Vrancea strong ground motions on the behavior factors and the related parameters that accounts for cyclic structural deterioration due to inelastic response. A large number of integrated analyses, nonlinear response analyses and energy balance-based analyses were carried out and estimates were made on the behavior factors for inelastic SDOF systems controlled by flexure with stiffness degradation. The correlation between behavior
factors and damage level are investigated, using the Bozorgnia and Bertero (2001), improved damage index. It is shown that multiple ground motion of Vrancea type for Bucharest, may lead to an important increase of force and drift demand of structures that usually is not taken into account.