Reliability-Based Design (RBD) For Everyone: (No Monte Carlo Simulation Required!)

by Richard J. Bathurst, P.ENG., Ph.D., (M.ASCE), Professor at the Royal Military College of Canada and a research director at the GeoEngineering Centre at Queen’s – RMC, located in Kingston, Ontario, Canada,,

Serial Information: Geo-Strata —Geo Institute of ASCE, 2019, Vol. 23, Issue 1, Pg. 52-57

Document Type: Feature article

Abstract: In North America, the design of earth structures for transportation applications is most often carried out using load and resistance factor design (LRFD). In the U.S., the AASHTO LRFD Bridge Design Specifications are followed. In Canada, the primary code is the Canadian Highway Bridge Design Code. The premise behind LRFD is that when a limit state design equation is used with prescribed load and resistance factors, a minimum margin of safety, expressed as a reliability index b, or probability of failure, is assumed to be assured. Unless the design is at the point where the limit-state equation is satisfied, the true margin of safety in probabilistic terms is unknown. Furthermore, designers may have a choice of load and resistance models to use in a limit-state design equation. Because these models will have different accuracies, using different design models with the same load and resistance factors will result in different true margins of safety in probabilistic terms.

Subject Headings: Load and resistance factor design | Bridge design | Limit states | Probability | Model accuracy | Monte Carlo method | Safety | Standards and codes | North America | Canada


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