Automated Risk-Based Seismic Design Method for Optimal Structural and Non-Structural System Performance

The current research effort is geared towards development of an automated performance-based design environment to optimize structural and non-structural system performance and gaining better understanding of system design for minimum life-cycle costs. The automated design methodology starts with the definition of a performance-based optimization statement which can be formulated as: (1) Minimize the initial capital investment in the structural system; (2) Minimize the expected annual losses (EAL). A time-based performance assessment methodology, according to the next-generation of performance-based earthquake engineering, is used to compute the EAL of a given design. The approach considers three seismic hazard levels (2%, 10% and 50% probability of exceedence in 50 years). Inelastic time history analysis is used to evaluate structural response and to obtain engineering demand parameters (inter-story drift, and floor acceleration). Damage to the structural system, non-structural displacement-sensitive components, and non-structural acceleration-sensitive components is characterized using HAZUS fragility functions. From damage measures an estimation of the direct economic expected loss (in percentage of the building replacement cost) is obtained. The approach could be modified to consider other performance measures as casualties or downtime. A genetic algorithm (GA) is used to find optimum designs that solve the formulated optimization problem where EAL is incorporated into a GA fitness function along with initial construction cost for an example building. Sample results provide optimum designs on the Pareto-front that can be used as decision-making tool for guidance as to how a design should be adjusted to either reduce the potential for damage, or to avoid excessively costly construction practices, while maintaining desired earthquake protection.