Simplified Erection Guidelines for Double I-Girder Systems during Bridge Construction

In the current design specifications, only the individual girder inside the double girder system is checked for lateral torsional buckling between the intermediate cross-frames. However, the overall lateral torsional buckling of double girder systems may be critical under bridge erection, due to the limited lateral bracing present at this stage. Therefore, close attention should be paid to the overall stability of double I-girders during construction, and research has been conducted for the simply supported case and the cantilever case under self-weight only. The results are presented in this paper. Through extensive finite element analyses, established formulas on the overall lateral torsional buckling capacity of simply-supported double girder systems were verified and then modified for the cantilever case. A stability index L/S was developed for estimating the stability of double girder systems under erection, which equals to the ratio between the girder span L and the girder spacing S. Formulae were then derived for the maximum span L_max and the maximum stability index (L/S)_max, beyond which the double girder system would lose stability under its self-weight. Parametric studies were conducted to determine the dominant parameters for L_max and (L/S)_max for various girder sections with different spacing. A quick and reliable method was also established to check the stability of double girder systems under erection using the L/S ratio.