Study On Mechanical Properties Of PC Box Girder Considering High Temperature Spalling Of Concrete Under Fuel Tanker Fire

With the rapid development of the “the Belt and Road” and the “Thirteenth Five-Year Plan”,the development of the transportation system has shown a great prosperity in the east and a great development in the central and western regions.The use of hydrocarbon fuels such as gasoline is related to the overall development of the national economy,and bridge fires caused by traffic accidents on tanker trucks have become increasingly frequent.The bridge fires have gradually become one of the key research directions in the industry because of their abundant oxygen supply,rapid heating up and inconvenient fire rescue.Fire reduce the performance of concrete and tensile bar.Once the concrete explosive spalling at high temperature,ordinary steel and prestressed steel will be exposed to fire,and mechanical properties will rapidly degrade or even fail directly,it even led to the collapse of the bridge.seriously threatening the people's life and property security.Therefore,we should pay attention to the impact of high temperature spalling of concrete on the mechanical properties of prestressed concrete box girder.Based on the National Natural Science Foundation of China-Research on the analysis of effective prestressing force decay mechanism and bearing capacity of concrete bridges under fire(51308056).ANSYS was employed to analyze the temperature distribution characteristics of prestressed concrete box girder bridges under high temperature and the sudden change of temperature field caused by high temperature spalling of concrete,the decay laws of the effective prestress of the box girder and the change characteristics of the flexural capacity of the box girder after different spalling of concrete were studied.Reveals the development of PC box girder deflection at different spalling of concrete.The main research content is as follows:(1)The research results of domestic and foreign scholars were investigated.The research hotspots in the current field of fire resistance in bridges were tracked,the research content of this article was determined,the relevant characteristics of high-temperature spalling of concrete were summarized,and the spall characteristics of concrete structures were statistically analyzed,and the three-degree index of the box girder spalling of concrete were proposed and established,based on the three-degree index establish a high-temperature spall model for PC box girder.(2)The 35 m PC box girder was selected as the research object.The transient heattransfer analysis model was established by the large-scale general-purpose finite element program ANSYS.The high temperature spalling of concrete was controlled by using the life-and-death element technology.The temperature field of the box girder and the sudden change of temperature field after spalling the concrete were analyzed.The analysis results show that the high-temperature spalling of concrete leads to rapid expansion of the high temperature region of the box girder.The overall temperature of the box girder suddenly rises,which exacerbates the deterioration of the concrete depth and causes the mechanical properties of the stressed steel bar to suddenly decrease.(3)Based on the results of temperature field analysis,the burning depth of concrete and the degradation of prestressed steel strands under different spalling the concrete were obtained.The loss of prestress after the burning of concrete was obtained and the loss of prestress caused by high temperature creep of the strands was calculated.The prestress loss of the PC box girder affected by the high temperature spalling of the concrete under the fuel tanker fire was analyzed.The decay characteristics of the effective prestress of the PC box girder considering the high temperature spalling of the concrete under the fuel tanker fire were investigated.An evaluation model for prestress loss of PC box girder considering the effect of high temperature spalling of concrete was established.(4)The bending load capacity of PC box girder under different high temperature spalling of concrete was calculated,and the decay law of PC box girder under different high temperature spalling of concrete was revealed.A three-stage calculation formula for bending load capacity of PC box girder considering the influence of high temperature spalling of concrete is presented.Thermal-force coupling method was used to obtain the change path of the deflection of PC box girder considering the effect of high temperature spalling of concrete.The variation of deflection of different high temperature spalling of concrete was compared and analyzed.