End-warping bracings during the construction of steel bridges

Slight bracing of steel bridges to control end-warping of their compression flanges near the end-supports can be very effective in enhancing the load-carrying capacity of the main girders that are involved. Relatively little information is available, however, regarding the stiffness and strength requirements of end-warping bracings. The results of seven large-scale laboratory tests of different configurations of bracings, including plan bracing and corrugated metal sheets, used in a twin I-girder bridge to resist end-warping at support points are presented here. Bracing forces generated in the plan bracings of the test bridge were also compared with those obtained through an approximate analysis suggested by Eurocode 3 for the preliminary analysis of such bracings. Moreover, the bracing forces present in the cross-beam of the test bridge were obtained for different end-warping brace configurations that were employed. The bracings, both of the plan bracing type and of corrugated metal sheets, were found to effectively enhance the load-carrying capacity of the test bridge. Only relatively small forces were generated in the bracing bars to achieve such a substantial increase (by a factor of greater than 2.0) in the load-carrying capacity of the studied bridges.