Fire-resistance design of ultimate and serviceability limit states for Q690 high-strength steel plate girders under patch loading

This study numerically investigated the serviceability and ultimate limit states of Q690 high-strength steel (HSS) plate girders exposed to fire under patch loading. A shell element numerical model of the Q690 HSS plate girder was created using Abaqus software, and its accuracy was verified through experimental results. A comprehensive parametric analysis involving 512 numerical models was conducted to examine the effects of elevated temperatures, web aspect ratio, loading length, and web depth-to-thickness ratio. Because of the absence of specific design guidance in EN 1993-1-2 for Q690 HSS plate girders exposed to fire, the accuracy of the resistance model specified in EN 1993-1-5 that was applied to steel plate girders at room temperature was verified by employing the material properties of Q690 HSS at elevated temperature. The verification results revealed that the ultimate resistance of the Q690 HSS plate girder obtained from the resistance model in EN 1993-1-5 was considerably lower than that obtained from the numerical analysis. A modified resistance reduction function that applies to the Q690 HSS plate girder at room temperature was proposed based on the resistance model in EN 1993-1-5. Comparisons indicated that the accuracy of the resistance model in EN 1993-1-5 was improved when applied with the proposed resistance reduction function. Additionally, predictive approaches were introduced to determine the ultimate resistance, effective resistance, and effective stiffness of Q690 HSS plate girders in fire. The comparison with numerical results highlighted that the proposed approaches exhibited high accuracy and provided a sound basis for the engineering design of Q690 HSS plate girders.