How Strong Is Strong Enough?

When a structural element fails, it is often necessary to determine whether the element was properly designed, fabricated, constructed, and maintained. Among the many things that such a determination requires is an appropriate benchmark strength; i.e., a capacity that can be compared with the loading that caused the failure in order to determine whether the element met the appropriate expectations. Establishing a rational benchmark is complicated by the fact that common industry design, fabrication, and construction methods can result in substantial and highly variable deviations from the actual strengths of structural elements relative to the corresponding nominal values. This paper uses first-order reliability methods—similar to those used to develop the current AISC LRFD steel design provisions—and other methods to arrive at a rational definition of how strong a particular element needs to be in order for it to be considered strong enough.