Two alternatives for implementing performance-based seismic design of buildings: Life -cycle cost and seismic energy demand.

Abstract

The inability of current seismic design codes to reliably predict building performance during earthquakes, and to satisfy secondary goals of controlling property damage and maintenance of building function in moderate and frequent earthquakes, prompted the earthquake engineering community to set its future target at performance-based seismic design. Of various methods proposed for the development of design methodologies for future design codes, two reliability-based methods are considered in this study. The first part of this research focuses on a design approach based on the optimization of life cycle cost, which is the sum of the initial building cost and the estimated damage cost due to seismic events during the lifetime of the building. Two moment resisting steel frame buildings are considered for this study. Seismic damage costs are computed for a large set of simulated ground motion records using the concepts of HAZUS<super>RTM</super>99 loss estimation methodology. Expected seismic damage costs for selected design lives of the buildings are obtained through Monte Carlo simulation. Optimum design strength of each building is selected by comparing life cycle costs of alternative designs. The results show that current codes should be made more stringent in order to achieve life cycle cost-optimum designs. Results of the optimization procedure are found to be sensitive to the selected design life and to two key parameters: cost sensitivity factor to weight change and discount rate. The second part of this research proposes a design checking methodology based on a probabilistic hysteretic energy demand criterion. Hysteretic energy demand is considered to be the best means for quantifying structural damage. Probabilistic seismic hazard analysis is performed by constructing uniform hazard spectra for hysteretic energy demand at a specific site using simulated ground motions. An equivalent single degree of freedom system-based methodology is adopted for using the uniform hazard spectra information in demand assessment of multi-degree of freedom structures. Finally, a deterministic equation is developed for checking the target probabilistic performance criterion for the building. The proposed procedure allows a designer to check a design for a target probabilistic criterion without performing any nonlinear time-history analysis or any uncertainty analysis.