Fire hazards represent one of the most important threats to the building environment with significant economic consequences for society and most dangerous threats to life. According to the mortality valuation of the WHO, fire causes the highest death toll of all types of damage to building structures. Fire engineering is the key discipline to improve fire safety in the building environment in a cost-effective manner. In high-rise buildings, bridges, industrial halls etc. primary and secondary structural members can be subjected to fire. The thorough analysis of the structural fire behavior and load bearing capacity of these members at elevated temperatures is essential. Plate girders are structural elements frequently used in constructions to address the challenges of structural design involving heavy loads and/or long spans. This feature makes plate girders the structural members of the first choice for transfer beams to provide column-free floor space for buildings, and primary structural elements in small to medium span bridges. Steel-plate girders are fabricated by connecting narrow flanges and slender web plates with welded joints. These girders are used frequently in combination with a concrete slab that is connected to the girder with shear studs to form and act as a steel-concrete composite section. As a consequence of the slender cross-sectional proportions, the webs of plate girders are highly susceptible to out-of-plane shear buckling.

The structural behavior of steel plate girders is becoming well understood, but only limited research has been conducted to predict the web shear strength of composite girders both at ambient and elevated temperature. The study of the shear strength of composite girders requires special attention in predicting their performance when subjected to a fire hazard. Experiments on steel plate girders have shown a reduction in shear strength of up to 50% even for temperatures below 400°C, while numerical studies have indicated that additional thermal restraint forces may further deteriorate strength of girders and may change a flexural failure mode into a shear dominated mode. Additionally, EN 1994-1-1 neglects the contribution of the concrete slab on the shear bearing capacity of the steel plate girders.

In the context of this project, experiments on suitably sized composite plate girder specimens using a test furnace will be conducted to provide an insight into their fundamental behavior at ambient and elevated temperatures; numerical simulation model will be generated and validated using experimental results to understand the failure mechanisms both qualitatively and quantitatively; an analytical model used to accurately predict the structural fire performance will also be developed.