Calibration of Current Factors in LRFD for Steel

An independent review of the bases for the development of resistance factors found in the American Institute of Steel Construction's (AISC) 1986 Load and Resistance Factor Design (LRFD) Specification is provided. The objectives of this paper are to critically evaluate claims found in a recent paper regarding the validity of these factors, to review and investigate the probabilistic approach taken in the development of these factors, and to examine the implications for design. Consideration is given to the reliability levels associated with established φ factors, as well as the implications for design of using a larger dead‐load factor than is currently used. It is shown that, while an analysis of allowable stress design (ASD) criteria indicates little consistency with respect to relative safety for different load combinations, a relatively consistent reliability (about β=2.6) was assumed in the development of resistance factors for steel beams in flexure. Finally, while improved methods for estimating dead load may be warranted, an arbitrary increase in the dead‐load factor may be overly simplistic and result in excessively conservative designs.