Structure Condition Study On Fire In Box-girder Of Continuous Rigid Frame Bridge

The probability that the bridge catch fire is low, while there is not a few fire accidents occoured on the bridge annually. After been fired, the characteristic of the material of the bridge would be changed tremendously, which could lead to the growing deformation, cracked, a sharp decline in carrying capacity and so on. Once the bridge disrepaired and then collapsed, the oversight issues in heavy loss.Nowadays, analysis on fire is mostly concentrated on the strength and deformation characteristics of various reinforced concrete structural elements in the building such as beams, columns, slabs, walls etc, but less on pre-stressed concrete contiuous rigid structure, such as the fire in the continuous rigid structure bridge.At the afternoon of Sept.3. 2009, the Gao. Bridge catched fire in the mid-span box-girder, the entrance to bridge had been block up, which lead the whole city get into difficulties. The current "Design of Concrete Structures" (GB50010-2002) can only calculate concrete structures at room temperature, and there is no corresponding high-temperature safety assessment rules of bridge to follow. Therefore, the change of state of rigid frame bridge caused by fire in the box girder need to be studied.Based on the theory and algorithm of Heat Transfer and by use of the Finite Element method,the thesis created the model of box girder with varying section, which is an exploratory research on the fire analysis in bridge. At the beginning, the theory of finite element method on temperature field analyses is explained proceeding from the general format of finite element of calculating the temperature field of the transient state, three-dimensional basic equation of the heat-conduction and the hexahedron isoparametric. And then, according to the case analysis of the bridge box-girder and the thermal performance of steel and concrete material under high temperature, the pre-stressed reinforced concrete fire model is analyzed by using the powerful analysis software on the basis of finite element theory. The main law of the prestressed reinforced concrete construction temperature field distribution and the stress characteristic of the birdge is drew. Finally, based on the box-girder fire of Gao bridge, by use of the ABAQUS Finite Element software the model of box-girder has been created. When the pre-stressed reinforced box-girder was build, the deflection, stress and deformation of cross section of the bridge was analyzed in detail. And then, it can be compared with the monitoring data of the fire bridge which verified the achieved reliability of the method. It is a useful trying of the way of simuliation fire in the box-girder of prestressed reinforced concrete bridge by the Finite Element method.In the thesis, the reasearch on fire in the box-girder of Continuous Rigid Frame Bridge works to promote the investigation on fire in box-girder of reinforced concrete bridge. It has a wider significance in evaluating the safty of the bridge, and then draws up scientific and reasonable repairing, reinforcing and maintenance strategies.