RISK BASED MINIMUM LIFE-CYCLE COST DESIGN OF ASEISMIC STRUCTURES

The current reliability-based probabilistic limit state design is based on notional failure probability of structural components, which cannot explicitly consider the consequences of earthquake events in terms of seismic loss, life-cycle cost, or even fatalities rate. Therefore, it is necessary to move from reliability-based design toward risk-based design by using the quantitative risk analysis tools. This paper reviews some existing models of risk-benefit-cost criterion for seismic design of structures, and then put forward a new model of life-cycle cost, which includes the minimum initial cost and the expected seismic loss under the future earthquakes during the design reference period. A two-stage minimum life-cycle cost design procedure is presented, in which the decision of the optimal fortification intensity (OFI) is made during the first stage, while the minimum-cost design under the optimal fortification intensity is undertaken in the second stage. The functional relationship between the minimum initial cost and the fortification intensity is derived through a series of minimum-cost seismic design subjected to the codified provisions by successively adjusting the fortification intensity. The expected seismic loss is the sum of the products of damage state probabilities with the corresponding economic losses. The probabilistic seismic risk analysis is deconstructed into four constituents: probabilistic seismic hazard analysis (PSHA), probabilistic seismic fragility analysis (PSFA), probabilistic seismic safety analysis (PSSA) and probabilistic seismic damage analysis (PSDA). The proposed methodology is applied in seismic design optimization of steel frame buildings subjected to Chinese seismic design codes. A numerical example demonstrates the feasibility and prospect of this new paradigm.