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

In 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 during bridge erection because of 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 was conducted for the simply supported case and the cantilever case under self-weight only. Through extensive finite element analyses, the formulas developed by Yura and colleagues on the overall lateral torsional buckling capacity of double-girder systems were first verified for the simply supported case and modified for the cantilever case. A stability index L/S was developed for estimating the stability of double-girder systems during erection, which equals the ratio between the girder span L and the girder spacing S. Formulas 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 during erection by using the L/S ratio.