ESTIMATION OF SEISMIC ENERGY DEMAND FOR USE IN EARTHQUAKE RESISTANT DESIGN

Abstract

Recent developments in the seismic design philosophy in past few years based on the energy absorption capacity in various forms is an attempt to shift from the current strength-based design approach. Different performance criteria for earthquakes of different probabilities of occurrence are currently prescribed in terms of different range of maximum drift ratios and plastic rotation capacity as a simplified representation of different demands. The limits on drift ratios and plastic rotations do not ensure satisfactory performance of the structure in case of a strong and long duration earthquake. Alternatively, energy demand is thought to be a more suitable design parameter. Being a more appropriate parameter than drift ratio and plastic rotation capacity, hysteresis energy can be used as a basis for seismic design of structures. The current seismic design philosophy in codes is based on elastic force which is reduced by a response reduction factor. The strength demand is applied to the structure by a suitable combination of different load types (gravity, imposed, seismic, snow, etc.). The demand is reduced using response reduction parameter which takes into account the ductility of the structure. The structures are designed to remain elastic for this reduced demand and are expected to go into inelastic range during extreme events. Performance of the structure depends upon its capacity to absorb inelastic deformations. Many researchers have advocated the use of hysteresis energy demand as a more stable parameter for structural damage. Our objective is to characterize performance levels (e.g. 10-Immediate occupancy, LS-Life safety, CP-Collapse prevention) in terms of energy dissipation. The nonlinear dynamic analyses for 3D building models of different structural configurations, designed according to current Indian Standards, are carried out for a suite of different earthquake ground motions. Hysteresis energy is normalized with respect to total p input energy to use it as a limit state