Structural Reliability and Sustainable Resilience

Current structural design methods are generally based on an iterative approach of member sizing after subjecting a system to a suite of load combinations, and then selecting the governing combination for each member. With the recent emphasis on performance-based design, it is important to advance this concept into the next realm, and ask what the consequence is of individual member behavior on the performance of the structural system. In a reliability and multiple performance framework, this is a generalization of the notion of progressive collapse. A major objective of this paper is to define the sensitivities of current code philosophy on the overall design. Structural system reliability concepts are adapted for multiple performance evaluation of systems with multiple levels of interdependent limit states, and some ideas are indicated for new approaches. This concept is further extended from a system composed of members of an individual building to a community scale, where a suite of structures forms the set of basic units, rather than individual structural members. The resilience function for the community served becomes the objective function, in place of the reliability of a single structure. By defining the resilience of a community through the relationship of its building reliabilities, structural design becomes an inherent tradeoff for societal investment in structures in terms of their role for community physical, social and economic well-being.