Effects of Geometric Imperfections on the Bracing Performance of Cross Beams during Construction of Composite Bridges

Abstract

Steel girders require stability controls for different construction stages before the lateral-torsional support from the concrete deck occurs. The load-carrying capacity of bridge girders and bracing forces generated in their bracings are very sensitive to the girders' initial imperfections in terms of both the magnitude and distribution along the span. Relatively little knowledge is available in this matter; however, decisions on the worst shape of imperfections that gives a conservative resistance and/or maximizes the bracings forces is often not an easy task in practice. The present paper reports the test results (in terms of the load-carrying capacities and bracing forces) of a large-scale bridge of twin I-girder type in which the location of the intermediate cross beam was varied across the depth of the main girders. Moreover, extensive numerical investigations were performed to study the effects of some relevant shape of imperfections on both the load-carrying capacities of the studied bridges and the magnitude of bracing forces generated in the cross beams that were involved. The test results showed that the load-carrying capacity of steel girders can exceed their lowest theoretical eigenvalue because of the presence of initial imperfections. In the finite-element analyses of the studied bridge cases, in some cases, the girders followed their shape of geometric imperfections and reached a load value that was greater than the lowest eigenvalue of the systems.