EVALUATION OF CYCLIC DEMAND IN DUCTILE RC STRUCTURES

The emergence of performance-based seismic engineering principles, which are largely based on deformation-controlled design, has brought renewed focus on nonlinear structural analysis and the effects of cyclic demand and deterioration on seismic performance of structures. This paper explores the relevance of cumulative damage, arising from considerations of low-cycle fatigue, in establishing performance criteria for seismic design and evaluation of structures. A comprehensive evaluation of single-degree-of-freedom (SDOF) systems, representing ductile reinforced concrete structures, subjected to a large database of earthquake ground motions is carried out to establish the role of critical system and ground motion parameters on cyclic demand. Cyclic demand relationships are developed for numerous system variables to aid in the understanding of low-cycle fatigue effects on seismic response of generic RC structures. It is demonstrated that the characteristics of the system such as fundamental period and energy dissipation capacity and ground motion characteristics such as input energy play a significant role in the cyclic demand imposed on a structure during severe earthquakes.