Safety of Structures in Strong Winds and Earthquakes: Multihazard Considerations

In accordance with the ASCE Standard 7-05, in regions subjected to wind and earthquakes, structures are designed for loads induced by wind and, separately, by earthquakes, and the final design is based on the more demanding of these two loading conditions. Implicit in this approach is the belief that the standard assures risks of exceedance of the specified limit states that are essentially identical to the risks inherent in the provisions for regions where only wind or earthquakes occur. We draw the attention of designers, code writers, and insurers to the fact that this belief is, in general, unwarranted, and that ASCE 7 provisions are not risk consistent, i.e., in regions with significant wind and seismic hazards, risks of exceedance of limit states can be up to twice as high as those for regions where one hazard dominates. This conclusion is valid even if the limit states due to wind and earthquake are defined differently, as is the case in ASCE 7. We propose an approach to modifying ASCE 7 provisions which guarantees that risks implicit in minimum ASCE 7 requirements for regions where one hazard dominates are not exceeded for structures in regions with strong wind and seismic hazards.