Multi-objective optimization for probabilistic performance-based design of buildings using FEMA P-58 methodology

Abstract

This research presents an automated performance-based optimal design process by integrating a multi-objective optimization algorithm and a comprehensive probabilistic performance assessment method. This process is used to provide a set of design options that comply with the minimum code requirements and are optimal in terms of both initial cost and mean annual repair cost. The FEMA P-58 methodology is utilized as a modern performance-based methodology to determine the various performance measures such as repair costs, repair time, casualty rates, environmental impacts, and unsafe placarding for the design alternatives. To account for uncertainties in the magnitude and intensity of future earthquakes, the time-based assessment, and to account for inherent uncertainties affecting seismic performance, the Monte Carlo procedure is performed in accordance with FEMA P-58 guideline. The optimization process is carried out using a well-known multi-objective optimization algorithm called NSGA-II for three example office buildings with 3-, 6- and 9-story steel moment frame structures. For each building, a detailed performance model including a set of fragility functions for the structural and non-structural components as well as contents typically present in the building is considered. Three optimal design options are selected from the Pareto front set obtained for each building based on different optimization objectives. They are compared with each other and with the other design alternatives in terms of various performance metrics under different ground motion intensities. The contribution of structural components as well as drift-, acceleration- and velocity-sensitive non-structural components to the repair costs of these optimal designs is investigated. It is shown that drift-sensitive nonstructural components have the largest contribution to the repair costs of optimal structures. The contribution of these components in earthquake events with a 29% probability of exceedance in 50 years (29%/50 yrs) is on average about 71%, which decreases to 55% with increasing seismic intensity to 3%/50 yrs.