Effects of External Cross-Frames on the Ultimate Behavior of a Twin Steel Trapezoidal Box-Girder Bridge

In the construction of a twin-steel box-girder bridge, external cross-frames are temporarily used to increase torsional resistance. These members are regarded as secondary and are removed after a composite action in the bridge is achieved. Recently, attention has been paid to the possibility that external cross-frames can be a redundant source in bridges with girder fractures. In this study, the effects of external cross-frames on a damaged bridge were investigated using finite-element bridge models. Therefore, full-scale bridge models of a twin-steel trapezoidal box-girder bridge were constructed using K-type external cross-frames. Various failure modes, including the buckling and yielding of the cross-frames, were incorporated into the bridge models to account for realistic behaviors in the damaged bridge. The analysis results showed that the external cross-frames increased the load-carrying capacity of the bridge with one-girder fracture damage by transversely redistributing the live loads.