Minimum lifecycle cost design under multiple hazards

Design of structures against multiple hazards has become an important consi deration for many important engineering facilities such as major structures and bridges. A central issue is proper consideration of the uncertainty in the demand and capacity and the balance of reliability against costs. In t his study this problem is investigated based on minimization of expected li fecycle cost. The uncertainties in the loads and resistance are modeled by random processes and random variables. Costs of construction, consequences of structural limit states including damage, revenue loss, death and injury as well as discounting cost over time are considered. The importance of va rious design parameters is first examined by a parametric study. The method is then applied to design of a multistory office building against winds an d earthquakes in Los Angeles, Seattle, and Charleston. The sensitivity of o ptimal design to important but uncertain design parameters such as structur al life, discount rate and death and injury cost is investigated. The quest ion of uniform reliability against different hazard is also examined. It is found that an optimization-based design is a viable approach to design aga inst multiple hazards. The design is highly dependent on failure consequenc e and moderately sensitive to assumption of structural life span and discou nt rate. It may or may not be sensitive to death and injury cost assumption dependent on location and hazard risk characteristics. Uniform reliability against different hazards is not required. The design is often dominated, but not controlled, by the hazard that has large uncertainty and causes lar ge consequences. (C) 2001 Elsevier Science Ltd. All rights reserved.