Effective Energy Criterion for Collapse of Deteriorating Structural Systems

Abstract

The collapse of building structures during earthquakes has drawn much attention to the safety assessment and seismic design of structures to prevent their collapse. From the perspective of the energy flow during a dynamic event, an energy criterion for the dynamic instability of hardening structures under arbitrary excitations was previously developed. In this paper, the criterion is modified for the collapse identification of deteriorating structures, using an effective form of internal and external work applied to the structures. To account for the dynamic stability of a structural system at different damage stages, two time-varying energy indexes are introduced: one for the description of the structural properties, i.e., the effective intrinsic energy; and the other for the measurement of external work, i.e., the valid input energy. The first passage of the structural effective intrinsic energy over the valid input energy is shown to be an important indicator of the system instability that leads to the collapse of the structure. If the effective intrinsic energy is always less than the valid input energy during a dynamic process, the structure will survive. Collapse assessments are carried out with regard to the validity of the criterion as applied to three different deteriorating structures. The results show that the proposed criterion is able to depict the dynamic stability state and to predict the specific time of the collapse occurrence for deteriorating structural systems.