Study On Decay Mechanism Of Effective Prestress Of Concrete Bridges Exposed To Fire

In recent years with the rapid increase of traffic and the diversity of transportation, fire hazard as one of accidental has become one of the worst disasters of bridges. Bridge fire damages to a bridge, not only seriously affects the quality of traffic, leads to significant economic loss, even leads to the collapse of the bridge. Therefore, it is necessary to research the anti-fire properties of bridge.The body of prestress is a key fact for prestressed concrete bridge of fire resistance behavior subjected to fire.Based on study on "Analysis Method of Prestressed Concrete Bridges effective decay mechanism and bearing capacity in fire(51308056)", the main research contents are as follows:(1)Based on the research of scholars,give thermal parameters and mechanical parameters of the material suitable for the analysis of prestressed concrete girder bridge structure of fire temperature field and high temperature mechanical properties.Clear temperature curve of box girder temperature field analysis, heat conduction equations, boundary conditions,use ANSYS of the finite element program to solve box girder temperature field, obtain the temperature distribution of box girder when exposed to fire on one side and on three sides by fire.(2)Select three-span continuous prestressed concrete beam bridge as the research background,Based on the fire surface and the fire across of bridge, 12 kinds of fire conditions are designed.Basing on the terms of theoretica calculates the burning of the accumulated depth of concrete and the reduction in terms of area of steel. Holding the original configuration of the prestressed concrete box girder of not part of the fire on behalf of the special program midas civil calculate prestressed loss after burning, analysis the impact of the fire surface and the fire across on prestressing of steel beam, reveal the variation of the prestress loss of prestressed concrete beam under fire,establish formula of time on the prestress loss of concrete box girder under fire.(3)Based on the "highway reinforced concrete and prestressed concrete bridge design specifications"(JTG D62-2004), by section analysis method,research on the evaluation method of prestressed concrete girder bridge sectional effective prestressing attenuation under fire. Based on the evaluation criteria sectional effective prestressing reserve degrees, select a three-span prestressed concrete continuous beam bridge of the pier top section and the middle section of the across as key sections, calculated on three sides fire conditions across the second floor, the web and flange plate at the same time by the fire, when the fire extended 0min, 60 min, 120 min and 180 min the reserve value of sectional effective prestressing, conduct the overall rating of effective prestressing reserve of real bridge, determine the operating state of the bridge structure exposed to fire.