چكيده به لاتين
Bridges are public structures with minimum safety measures built to serve for several decades and various vehicles. Hence, they are exposed to different loads and the most severe hazards. In recent years, bridge fires have become a concern due to the increasing transport of hazardous materials (such as flammable materials, spontaneously combustible and poisonous materials). Over the past few decades, there have been many studies on buildings and tunnels fires, but up to date, there are no regulations for designing bridges in fire condition. Since the standard curves in the codes cannot be used for bridges due to the difference in the nature of the fire of bridges compared with buildings and tunnels, in this study, in addition to studying the steel bridge girders’ function and their failure time under standard fire loads, we used a natural fire curve obtained from an experimental open-air bridge fire study. In this study, first, two bridges with spans of 12 and 20 meters with a two-element beam-slab system and based on the AASHTO standard in CSI Bridge software were designed. One of the internal girders of each bridge was selected. Their thermal and structural response were analyzed under 12 fire scenarios, including three positions of fire (whole span, middle of span, and one corner of span) and four different fire curves (real fire in open air, hydrocarbon fire, ASTM E119 standard curve, ISO 834 standard curve) in ABAQUS finite element software. The results of studying the performance of these girders and estimating their failure time with the criterion of L / 30 of span under fire conditions show that the ISO 834 curve has the longest time compared to the other three curves and it seems that its conditions are far from the natural fire conditions of bridges; While the failure times related to the other three curves is close in most cases, and among them the hydrocarbon curve, due to its rapid heating rate, has the shortest failure time. However, the natural fire curve shows the failure time in the range of two minutes, which could indicate the need to strengthen these girders to withstand the fire.
