Mechanical Performance Analysis Of Fire Process And Post-disaster Evaluation Method Of Prestressed Concrete Girder Bridge

The basic construction of road and bridge has been developed rapidly at present in ourcountry. Most bridges, with high proportion in highway, are pre-stressed concrete box sectionbeam bridge. As various bridge disasters taking place frequently, fire cause serious threat tostructural security of bridge, even the risk of bridge collapse existed. It is necessary to studythe fire resistance of pre-stressed concrete box girder bridge on the condition of hightemperature fire. Due to the high cost of fire experiment, scaled ratio of scaled model andnon-simulation of complex boundary conditions, the bridge structure mechanical property inhigh temperature by finite element method is analyzed in this paper, aiming at pre-stressedconcrete box girder bridge. Main content as follow:With the study of the law on thermal parameter of concrete and pre-stressed iron varywith temperature at home and abroad, the indexes of thermal function suitable for the analysisto pre-stressed box girder temperature field are settled. Besides, the indexes of thermalparameters applicable to the analysis of pre-stressed box girder displacement field isdetermined by the domestic and overseas research on various mechanical properties ofconcrete and pre-stressed iron under and after hyperthermia changing with temperature.Basic method and steps of solving temperature field are finite element deduced, based onfundamental thermodynamics theories. With transient analysis method, the temperaturedistribution law of box girder fire disasters under standard fire curve is obtained by nonlinearanalysis towards fire temperature field of box girder mid-span section. Moreover, temperaturefield calculating software is made through secondary development of ANSYS to provideevidence for establishing temperature field distribution of hyperthermia bridge section.Theoretical derivation is made by the process of solving cohesive prestress structuredisplacement field with finite element method. On this basis with thermal structure method,hyperthermia displacement field of pre-stressed concrete girder box bridges is nonlinearlyanalyzed and solved. Factors such as fire duration, fire position, length of flange plate, size ofexternal load, prestress degree, steel beam, thickness of protective layer, section size, lengthspan and concrete strength are calculated and analyzed in order to find the their influence law on deflection of girder box span. Main factors of influencing structure stress of pre-stressedgirder box bridge under high temperature are determined through the analysis of abovesensitivity parameters computation to provide evidence for the design of pre-stress girder boxfire-resistance.The procedure of damage diagnosis is provided for pre-stress concrete bridge after hightemperature and fire, base on multilevel fuzzy comprehensive evaluation method to determineevaluation factors and weights of concrete bridge. Evaluation model of pre-stress loss andconcrete strength reduction and girder body burning depth is built, adopted verticallyincrement method to test effective prestress after-fire.