Checking Steel Girder Stability during Erection—Rules of Thumb Modified by AASHTO LRFD

Until recently, (sub)contractors have been relied on rules of thumb on L/b ratios to check girder stability under erection, where "L" is the unbraced length and "b" is the compressive flange width. Certain limits on L/b ratios were developed, which dictate if a specific girder will remain stable, needs stability check, or requires temporary support during erection. Although the rules of thumb are very convenient to use on site, it is necessary to check these rules through the latest AASHTO LRFD code. Parametric studies were conducted to (1) determine the effects of girder cross-sectional configuration and material strength on stability during erection; and (2) check the rules of thumb on L/b ratios. From the study, it was concluded that (1) flange width and web depth have the most effects on girder stability during erection; (2) the combined effects of gravity and wind load control in most cases; (3) rules of thumb on L/b ratios were too conservative for cantilevers and unsafe for simply supported girders, and were therefore modified.