Study On The Bearing Capability Of Prestressed Concrete Box Girders Exposed To Fire

In the past few years, with the traffic volume increases gradually,the number of vehicles which loading inflammable and explosive materials increases too, The fire disaster will come along if traffic accidents occur. Bridge is an important part of the transportation network, if bridges are on fire, it will bring some serious consequences, such as casualties, property losses, traffic gridlock and rescue difficulty. Prestressed concrete box girder bridge simply supported is often used, at high temperature fire, the material properties and mechanical properties of concrete and steel will degenerate with the increasing temperature, then, the bearing capability of bridge changes.The research was supported by National Natural Science Foundation of China--stduy on analysis method of bearing capacity and decaying mechanism of effective prestress for concrete bridge subjected to fire(Grant No. 51308056). This article uses the finite element program ANSYS to analyze the temperature and bearing capacity of prestressed concrete box girder bridge which is on fire, reveale the relationship between the bearing capacity and fire time. The main contents are as follows:(1)The thermal parameters and mechanical properties of concrete and steel are selected by comparing the research results in domestic and foreign, such as thermal conductivity, specific heat capacity and thermal expansion coefficient, elastic modulus, strength and constitutive relation. The ANSYS software is used to build finite element model of prestressed concrete box girder, set different fire conditions, analyze the temperature distribution discipline of box girder which is on fire.(2)Based on the strength loss of virtualization layer section of the equivalence principle,calculate the accumulative burning depth of concrete, according to the relationship between the strength of prestressing steel and ordinary steel and temperature, calculate the strength of prestressing steel and ordinary steel after fire. Calculate the flexural bearing carrying capability of L/8、L/4、L/2 section, reveale the relationship between the flexural bearing capacity and fire time. Different failure criterias are defined and the failure time of bridge structure that is on fire is obtained based on the failure criterias;(3)Apply the calculation results of the temperature field as a load to the structure field by the thermo-mechanics coupled method. Analyze the P-S curve at different fire time of the middle section of the prestressed concrete box girder, determine the shear bearing capacity, analyze the crack of the prestressed concrete box girder in case of high temperature fire, reveale the relationship between the shear bearing capacity and fire time. Different failure criterias are defined and the failure time of bridge structure that is on fire is obtained based on the failure criterias;...