Study On Mechanical Working Performance Of PC Hollow-core Slab Girder Under Tanker Fire

As a extremely destructive accident,the fire disaster causes the losses up to ten billion yuan in China every year,which harms the people's lives and property extremely.Recently,the development on Chinese transportation industry and bridge construction all are rapidly,therefore,the bridge conflagrations frequently occur on plenty of constructed bridges.Accordingly,the bridge conflagration should be seriously considered in bridge design and construction.From relative documents and data,the frequency of bridge conflagration increases year by year after the end of 20 th Century.Actually,most of bridge conflagrations are caused by sudden accidents of tanker trucks.As we know,once the ruthless conflagrations occurred,the structure of bridges should be destroyed critically,which not only leads to the expensive maintenance and temporary bridges traffic,but also damages the economy of individual or social immeasurably.In China,the proportion of bridge transportation is high in total national transportation,which makes more and more scholars and experts focus on the bridge conflagrations.In recent years,foreign researchers have obtained lots of results on bridge conflagrations.Studies on mechanical properties of composed materials as concrete and steel bars in high-temperature are fairly rich,however,studies that take the mechanical behavior of the whole structure in conflagration scene as study object are less,especially studies on conflagration resistance of prestressed-concrete hollow slab beams.According to the study on analysis method of concrete-bridge effective prestressing decay mechanism and bearing capacity in conflagration by National Natural Science Foundation of China(51878057),this paper takes generally-used hollow-core slab girder as the study object to study on mechanical behavior of prestressed concrete hollow-core slab girder in conflagration scene by applying the finite element computing program in calculation and setting up the analysis model by using thermo-mechanical coupling method.The main content are as follows:(1)The 20 mPC hollow-core slab girder is taken as the research object,andestablishes a analysis model of finite element heat transmission and analysis model of coupling of thermal and mechanics.Meanwhile,it obtains thermodynamics parameter values,establishing process and details of analysis of accurate finite element model.(2)Setting the different fire accident situation for PC hollow beam girder as FC1,FC2,FC3 performance condition,reasonably selected the temperature measuring point of concrete,prestress steel bundle and plain steel bar in different measuring fields.Analyzing the concrete temperature field,prestress steel bundle temperature and plain steel bear temperature according to this.(3)According to equivalent principle on strength loss of virtual-layer section,post-burn strength of common steel bars and prestressed steel tendons is calculated based on high temperature mechanical properties of steel bar,after the burning depth conversion on the concrete.Normal-section flexural capacity of prestressed-concrete hollow slab beams is calculated,calculation formula on flexural-capacity attenuation of prestressed-concrete hollow-core slab girder normal section is fitted and flexural-capacity failure time of prestressed-concrete hollow-core slab girder normal section is give,in three conflagration conditions.(4)Based on the analysis of temperature field,this paper discusses the influence on hollow-core slab girder deflection,which is effected by thermal-mechanical coupling of prestressed-concrete hollow-core slab girder and caused by the factors as load level,fire location as well as prestressing degree.Finally,fire endurances of prestressed-concrete hollow-core slab girder are given.As the prestress increases,the fire resistance of prestressed-concrete hollow-core slab girder increases significantly;As the load level or fire sections increases,the fire resistance reduces correspondingly.