| As one of the factors that affect the safety of bridges,fire has gradually received extensive attention.The continuous high temperature in the fire,fire extinguishing methods,etc.may cause permanent damage to the bridge structure,or even cause the bridge to collapse.It is an important subject to study the change of fire bearing capacity of concrete prestressed box girder during fire.According to relevant literature,this paper collects and adopts C50 concrete,HRB335 rebar and Strand1860 steel strand,its thermal and mechanical properties under variable temperature environment.According to the JTG D62-2004 specification,combined with the calculation method of the composite beam section,a set of methods for calculating the normal section flexural bearing capacity of the concrete prestressed box beam section during the temperature change is derived.The main research contents of this article are as follows:(1)Using the COMSOL Multiphysics finite element software,a time-domain numerical simulation analysis model of the concrete prestressed box girder during fire was established,the temperature gradient of the box girder section heated and analyzed,and a general calculation formula was given.During the heating of the box girder,the non-uniform distribution of the mechanical properties of the section due to the uneven distribution of the temperature field of the section is analyzed by dividing it into a composite beam through the division of the virtual layer of Heating mechanical properties.(2)Using the exhaustive method,the formula for calculating the normal section flexural bearing capacity of the box girder during temperature change is derived,and the validity of the formula is tested.Then,using the calculation method deduced above,the whole process of the full beam normal section flexural bearing capacity check was carried out for the engineering example,and the fire resistance and fire resistance time were given.(3)After the box girder is heated by fire,the effect of cooling mode on the temperature field is studied.Calculate the creep loss of the box girder prestress during the heating stage,and study the prestress loss due to plastic strain after the box girder is cooled by fire.Finally,the change of the flexural bearing capacity of the normal section before and after the box girder is fired and the degree of bearing capacity redundancy are studied. |
