Damage Evaluation of Composite Beams Under Fire Conditions

This paper presents a numerical method for damage evaluation of steel structures under fire conditions based on degraded material property values. As the measure of structural damage to fire, a damage index is proposed which indicates how much a structure loses its material strength when exposed to fire. The index is formulated with the ratio of a volume-weighted average of material strength at elevated temperatures to that of the strength at room temperature. To investigate the feasibility of proposed damage index, fire testing and the corresponding structural fire analysis of steel–concrete composite beams are performed using a design fire load. The fire is modeled using a standard fire curve proposed in American Society for Testing and Materials E119. A regular real-scale composite beam and the beam protected by a fire-resistant material layer, the latter of which is typical of structural members used in nuclear power plant buildings in Korea, are considered for the fire damage evaluation. The damage state of the composite beams is evaluated using the fire damage index at each time the fire progresses, and it is compared with the value of the post-fire damage index of the beams. By the use of the proposed damage index, the effect of fire-resistant materials on structural integrity is quantified, and it is investigated whether the damage state of each beam at the end of the fire load satisfies the design performance of composite beams used for nuclear power plant structures.