Study On Fire Resistance Of Prestressed Concrete Box Girder

Because of the rapid development of highways and bridges and the multiple means of conveyances as well as the increasing pipeline transportation vehicles in China,the fire hazards became increasingly frequent on the bridges.Different from the housing construction,the fire protection system is not generally taken into serious considerations in the bridge design.Since the bridges are commonly located in the open environment and the air circulates unhindered,the security and durability would be seriously influenced and carrying capacity may be decreases once the fire occurred.The simply-supported box girder of prestressed concrete is featured with simple structure and easy construction as the common structures in bridge engineering,which is of significance for the studies of fireproofing.This paper is supported by the natural science fund of Study on Effective Prestress Decay Mechanism and Load Carrying Capacity Analysis of Concrete Bridge under Fire.Based on the simply-supported box girder of prestressed concrete with size of 20 meter,the numerical simulation model of ANSYS was employed to analyze the temperature distribution of the prestressed concrete under fire with high temperature.Besides,the variation of flexural capacity on the normal section and the middle span deflection with time were also studied and the main research contents are listed as follows:(1)Based on reviewing the achievements and relevant standards of domestic and international scholars,the necessary thermal parameters of the prestressed concrete and mechanical behavior under high temperature were confirmed.Furthermore,the model of transient heat transfer was established by using the computation procedure of ANSYS.It is also analyzed that temperature distribution in prestressed concrete under fire with high temperature.(2)On the basis of the equivalence principle of the strength loss,the depth of the burning for the concrete was calculated,According to the mechanical behavior under high temperature,The strength of Steel-bar and prestressed reinforcement after fire was also computed.The calculation of the flexural capacity of the normal section of the prestressed concrete box girder under high temperature fire is carried out.,the variation of the flexural capacity with time was investigated and the equation of attenuation of flexural capacity for the normal section of box girder under high temperature.Finally the fire destroying principle based on the resistance was drawn.(3)The method of coupling thermal and mechanical was adopted to analyze the prestressed concrete in fire process.It is analyzed that the variation of the middle span deflectionin in the prestressed concrete and the development feature of fissure.Besides,the effect of the degree of prestress on the prestressed concrete box girder fire resistance was studied and the deflection failure criteria under different prestressing degree was given out.The comparative study of the temporal and spatial variation of the deflection of the box girder was conducted.