Lateral bracing of steel bridge girders by permanent metal deck forms

Lateral torsional buckling is a failure mode that often controls the design of steel bridge girders during construction. Bracing in the form of cross-frames and diaphragms are often provided at locations along the bridge length to reduce the unbraced length and increase the buckling capacity. Although they are not currently relied upon for bracing, permanent metal deck forms (PMDF) are frequently used to support the wet concrete for the bridge deck during construction. Similar forms used in the building industry are commonly relied upon for beam bracing. The main difference between the forms used in the building and bridge industries are the method of connection. In the building industry, the forms are typically fastened directly to the top girder flange. In the bridge industry, the forms are supported on a cold-formed angle that provides convenience with some constructability issues but leads to eccentric connections that substantially reduce the stiffness of the PMDF systems.; The objective of the research study outlined in this report is to improve the understanding of the bracing behavior of PMDF systems used in the bridge industry as well as to develop improved connection details between the support angles and the girder flanges. The research included laboratory tests and finite element analytical (FEA) modeling. The laboratory studies included shear tests and full scale testing of a twin girder system with a 50 ft span. Both lateral load tests and buckling tests were conducted on the twin girder system with PMDF for bracing. In addition to demonstrating the behavior of the bracing systems, laboratory studies where also used to validate the computer models of the bracing systems so that parametric FEA studies could be conducted.; Modified details for the connection angles consisted of stiffening angles that span between adjacent girders at intermediate locations along the girder length. Stiffening angles substantially increased the stiffness of the PMDF system. The modified details make PMDF systems a viable bracing alternative in steel bridges that can significantly reduce the number of cross-frames and diaphragms required for stability bracing.