Using Metal Deck Forms for Construction Bracing in Steel Bridges

Abstract

Metal deck forms are frequently used in the steel building and bridge industries as formwork for the wet concrete slab. Although the forms are often relied on for stability bracing during construction in buildings, conventional connection details between the forms and girder top flanges in the bridge industry possess an eccentricity that limits the bracing performance of the forms. A research study to assess and improve the bracing potential of permanent metal deck forms (PMDFs) used in bridge applications was conducted. Recommendations from the research study were implemented on two steel I-girder bridges located on the IH-610 north loop in Houston. The use of the PMDF bracing resulted in the elimination of 680 intermediate diaphragms from the bridges. Before the implementation project, laboratory buckling tests were conducted on a twin-girder system with members and bracing that were identical to those used in the implementation project. To the authors' knowledge, this project represents the first time that metal deck forms were relied on for stability bracing of steel I girders in the bridge industry. This paper documents laboratory testing, design, and construction of the two bridges in which PMDFs were used as construction bracing for the steel I girders in the bridge superstructure. Laboratory test results showed that the forming system, which was at the lower span limit of PMDF systems frequently used in steel bridge systems, could provide suitable bracing for the two implementation bridges. Using metal deck forms for bracing, the bridges were designed with no intermediate diaphragms/cross frames. A total of 680 intermediate diaphragms that would have been required in a bridge with conventional bracing were eliminated. The implementation of the research recommendations in the design of steel bridges can result in substantial improvements on the efficiency and economics of bracing systems for steel bridge superstructures.