Convenient Method for On-Site Check of Single Steel I-Girder Stability during Erection

Abstract

The behavior of a single steel I-girder during erection is quite different from that of a girder under service: the girder during erection usually has limited or no lateral bracing along the span. Elastic lateral torsional buckling of the steel girder may occur if the girder span becomes too large. Rules of thumb have been used to check girder stability during erection by using the ratio of unbraced length L to compression flange width b; this is based on experience. For any longitudinally unstiffened girder section, formulas were developed on the basis of the current AASHTO load and resistance factor design code for the unique maximum L/b ratio. Parametric studies were then conducted to calculate Lmax and the (L/b)max ratio for a variety of girder sections that cover the range of practical design in order to identify dominant section parameters on the (L/b)max ratio as well as girder stability during erection and to develop simplified formulas for the upper and lower bounds of the (L/b)max ratio for all girder sections within the range of practical design. On the basis of the simplified formulas, an on-site check of single steel I-girder stability during erection could be conducted by checking the girder L/b ratio against the (L/b)max ratio for that given section or, even more easily, by checking the girder L/b ratio against the upper and lower bounds of the (L/b)max ratios for all girder sections.