Experimental study on residual bearing capacity of full-size fire-damaged prestressed concrete girders

Abstract

With the increasing development of three-dimensional transportation network, the probability of bridge fire accidents is increasing year by year, which leads to reduced bearing capacity of the bridge exposed to fire. Existing bridge detection and evaluation methods are not suitable for bearing capacity evaluations of fire-damaged bridge, since material degradation or localized damage of structural members caused by elevated temperature are not considered. This paper took actual fire-damaged bridge as a case study to analyze the influence of fire on residual bearing capacity as well as bending test on two 20 m span hollow slab girders with different degrees of damage. The prestress loss, failure mode, load–displacement curve, and residual bearing capacity were tested. A method integrated the FDS (Fire Dynamics Simulator) and the FEA (Finite Element Analysis) was proposed to calculate the actual process of bridge fire and mechanical property of fire-damaged girders. The dimensional temperature fields around the bridge and internal temperature field in a concrete hollow slab girder during the fire were obtained. Based on the research results of mechanical properties of concrete and prestressed tendon under elevated temperature, the mechanical numerical model considering internal temperature field was established; The failure mode and residual bearing capacity of fire-damaged girders were simulated. The results show that the post-fire residual bearing capacity mainly depends on the maximum temperature of prestressed tendons. The higher the temperature of prestressed tendons is, the lower the residual bearing capacity is. In the case bridge, compared to the girders at ambient temperature, bearing capacity of the two test girders decreased by 17.6 % and 15.1 %, respectively. The method proposed in this paper can be used to evaluate the post-fire bearing capacity of fire-damaged concrete girder bridges.