Prestress loss of concrete bridge with box girder based on strength reduction exposed to fire

To study the variation relations between the prestress decay amplitude of concrete bridges and high temperature,based on the virtualization equivalence principle of the concrete strength loss,fire conditions were designed to analyze the temperature field of concrete bridge with box girder under single-side fire and three-side fire,and the thermo-mechanics coupled method was adopted to calculate the prestress distribution along the bridge span of concrete bridges with box girder at various fire time and disclose prestress loss law of concrete bridges with box girder exposed to high temperature based on strength derogation of concrete.The results show that:the temperature generally presents a layered distribution when the floor of concrete bridge with box girder is exposed to fire.When the floor and both sides of the web of concrete bridges with box girder are exposed to fire,the temperature generally presents an U-type distribution,and the temperature peak value at intersection is higher than that of in other parts.With the increase of the fire time,high temperature layer gradually extends inward and distribution width expands.Prestress loss of steel strand located at the bottom of the web is relatively more than it located in the upper position of the web,prestress loss at the quarter of span is more than that of other parts and its value is about 1.1times than that of other parts.The increase amplitude of prestress loss at mid span is more than that of other parts,and the maximum growth rate is about 9.4%.Prestress loss loacated in anchor has a minimum value,and prestress loss along span presents an inverse W-type during various time steps.The research can provide a guideline for fire-resistant design and assessment of prestressed concerte bridge after fire hazard.