Web Shear Buckling of Steel Plate Girders Under Fire

Abstract

Despite the fire hazard to highway bridges, their fire and post-fire performance remain poorly understood. Historical evidence has shown that steel plate girder bridges are particularly susceptible to significant damage or collapse during a fire. Typical bridge fires involve a vehicle, such as a tanker truck, crashing beneath, adjacent to, or on top of a bridge, with its onboard fuel and cargo igniting in the process. Previous case studies of fire-damaged steel plate girder bridges indicate that diagonal buckles form in the web, suggesting that web shear buckling may be a significant factor in the fire performance of these bridges. Therefore, the main research objective is to understand the fundamental shear buckling mechanics of deep plate girders at ambient and elevated temperatures such that the safety of these structures may be improved.

The research results can be summarized into four major outcomes and conclusions. First, studies show that the FE results are particularly sensitive to the nonlinear material properties, which also have large variability that need to be considered. Second, a new physical model to represent web shear buckling was developed that is based primarily on the compressive response of the plate (as opposed to the typical tension-field response that is commonly used). This model correlates well to the experimental and FE results at ambient temperature, and also works well at elevated temperatures. Third, it is possible to improve the shear strength of steel plate girders by orienting the transverse stiffeners along the compression diagonal and insulating the stiffener (against elevated temperatures). Research, however, is needed to overcome the practical difficulty of thermally insulating the stiffeners. Finally, weathering steel material properties are similar to those of non-weathering steel at elevated temperatures.

The tools and insights cultivated by this PhD research contribute to developing a better understanding of the fundamental behavior (mechanics) of web shear buckling. This knowledge is necessary for improving the design of bridges to withstand fire loadings. Both academic researchers and practicing engineers may benefit from the work presented in this dissertation as contributions to the literature are offered on both a theoretical and practical front.