Evolving toward Project-Specific Reliability: Are We Sure It's a Good Idea?

Abstract

The writers of current standards and specifications for load and resistance factor design (LRFD) envisioned that those documents would be used by designers in a manner similar to that used in prior (allowable stress design) formats. They presumed that designs would be accomplished by satisfying a series of checking equations in which the structural resistance exceeds the demand on the structure. While these early developers used reliability analysis tools to derive the load and resistance factors, they did not envision that reliability analysis would evolve into a tool to be directly used by designers. In spite of those early presumptions, the evolving reality is that reliability analysis procedures are now available to an increasing number of individual designers. Sooner or later, these designers will attempt to use reliability analysis to assist them in their project-specific or, more likely, product-specific designs. This paper discusses limitations and potential pitfalls of reliability analysis when used in routine structural design. Specific examples focus on wood design. The conclusion reiterates the premise that LRFD, not theoretical reliability analysis, is the proper tool for use in daily design.