Risk Consistency and Synergy in Multihazard Design

Abstract

Current design procedures in the United States use the envelope of individual hazard demands on a structure to ensure safety against multiple hazards. A difficulty in multihazard design for wind and earthquake is that the load and resistance factor method makes use of different design philosophies developed by different subdisciplines. Seismic design explicitly allows for inelastic behavior. In contrast, wind design assumes that, before application of a resistance factor less than unity, the limit state is defined by the development of the first plastic hinge in a structural member. This paper focuses on the issue of risk consistency in multihazard design, and shows that, in spite of this difficulty, it is possible to quantify the risks of arriving at a particular lateral drift state for structures exposed to multiple nonsimultaneous hazards and to compare them to the risks for the same structures subjected to a single hazard. A second focus is the issue of multihazard design synergy. It has been pointed out that redetailing a building to current seismic codes can increase its resistance to blast and that structural efficiency and life-cycle cost are influenced by multihazard considerations. This paper shows that, for the case study of a 10-story steel-frame building, the use of reduced beam section (RBS) connections, intended to enhance ductility in seismic design, does not reduce the risk of structural damage caused by exposure to wind alone or exposure to wind or earthquakes.