Robust Simulation: Why and When Needed and What Should be Qualified

This paper first outlines how and why the authors have in the past defined “robust simulation” to be the employment of alternative credible quantitative evaluations of risks to systemic issues. Next, this paper outlines how structural engineering evaluations for severe winds and earthquakes may be considered as requiring this sense of “robust simulation” with respect to building codes and others issues. Diverse models of seismicity, strong ground motion attenuation, and performance of soils including possible liquefaction displacement analysis show how hazards may have very competitive alternative quantitative procedures. Different levels of evaluations of building responses to earthquakes and severe winds likewise show how there may be diverse but competitive alternative quantitative procedures and how these may on occasion illustrate catastrophic trajectories. After these discussions, there will be a brief discussion of how the ensemble of outcomes from diverse competitive models can assist rather than hinder the decision-making process. BACKGROUND AND INTRODUCTION In 1991 an NSF project ended that used at the time state-of-the-art portfolio risk methods for evaluating seismic design code levels. Results for users included two graphs comparing losses and casualties, respectively, for the City of Los Angeles in contrast to Salt Lake County. As expected, one graph illustrated how total losses were greater in the City of Los Angeles. The second graph, though, showed how for the same level of seismic design, average casualties were roughly the same. For extreme events, casualties per person exposed would be greater in Salt Lake City given the same level of seismic design as for Los Angeles buildings. Professor Larry Reaveley took results of this project to structural engineers very influential in code-making processes(Taylor et al., 1992). Two decades later, we discern projects designed to evaluate collapse potential in diverse regions in the United States (Luco et al., 2007). A similar code issue has arisen that now deserves a risk evaluation to assist decision-makers in deciding whether or not one needs to develop multi-peril design procedures that do not assume

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