Loss-based formulation for multiple hazards with application to residential buildings

Abstract

Most areas of the world are subjected to one or more natural hazards, such as earthquakes, tsunamis, hurricanes (cyclones), snow storms, wildfires, costal inundation or river flooding. In the United States, economic losses average about $5.4 billion annually from hurricanes and about $4.4 billion dollars for buildings a year from earthquakes. In addition, greater than 75% of declared Federal disasters are a result of flooding. This paper summarizes a loss-based formulation to evaluate the risk to buildings from multiple hazards, taking into account the different nature of the hazards, frequency of occurrence and associated return period for current codified design, hazard-resistant design philosophy and consequences. Structural reliability-based methods that describe natural hazard and structural system responses probabilistically are essential for quantifying expected losses from natural disasters and for developing appropriate strategies to manage risk. The formulation permits the main sources of uncertainty that affect building performance to be identified, and provides insight on strategies for effective multi-hazard mitigation efforts. Fragilities, defined as the conditional probability of various levels of losses as a function of hazard demand (i.e. wind speed, spectral acceleration, ground snow load, or flood depth), of typical residential buildings with two levels of hazard resistance standards are generated. Probabilistic descriptions of the various hazards at four representative sites are used to combine with the appropriate fragility to determine the annual probability of different levels of losses as well as the combination of all hazards and the resulting loss at each site. The comparative assessment of risks due to multiple hazards is desirable for public policy and disaster planning purposes, as well as for insurance underwriting.