Analysis Of Temperature Effect And Bearing Capacity Of Prestressed Box Girder Subjected To Fire

For the frequent occurrence of fire and the huge economic loss caused by fire,and the research of bridge fire has become a hot spot.The study of the temperature field distribution and the mechanical properties of the bridge after fire are of great significance for the safe operation of the bridge.This paper is based on the engineering example,and the ABAQUS finite element method is used to study the temperature field and stress analysis of the fire of the prestressed concrete box girder,and the bearing capacity of the fire is studied.The thermal performance and high temperature mechanical properties of concrete and reinforced materials are summarized.Research on prestressed box Girder in fire,the temperature field of box girder was analyzed by using HCM heating curve and ISO-834 temperature rising curve,and the temperature stress analysis is chosen as the temperature load.Temperature field analysis shows that: The temperature distribution of the bottom plate and the bridge deck is different under the condition of multi surface fire and single fire.The temperature of the edges of the bottom plate and the bridge deck is higher than that of the middle surface when the surface is under fire,and the temperature of both sides of the bottom plate and the bridge deck is lower than the intermediate temperature in the case of single fire.The temperature curve of the reference point on the fire surface and the reference point on the non direct fire surface is similar.The temperature of the same reference point increases with the increase of heating time.In the process of rapid temperature rise,the temperature of the reference point on the surface of the fire,in the vicinity of 700 degrees near the emergence of a gentle warming?a significant inflection point?,and the reason is that when the fire occurs,the external concrete will be damaged,which will lead to the loss of concrete.For different temperature curves,the influence of temperature field is not great,and the temperature rise curve of HCM is faster than that of ISO-834 standard heating curve,and the maximum temperature is slightly higher,but there is not much difference in the distribution of temperature field of box girder.The results of temperature field stress analysis show: When the ignition time is 10 min,the maximum Miss stress and the space deformation of the box girder structure are relatively small,and the deformation of the structure is increasing slowly.When the ignition time reaches 15 min,the maximum stress and the spatial deformation of Miss increased slowly,and tend to be gentle.And the maximum Miss stress of box girder is 5.76 MPa when the ignition time is 35 min,and it is more than the tensile stress strength of concrete(f_tk=2.65 MPa),and the maximum Miss stress is mainly distributed on the bottom of box girder,at the bottom of the outer table light beam concrete has come off,the maximum deformation is 2.58 mm,the deformation of the bridge deck is large.Research on prestressed box girder after fire,and the static load test of prestressed box girder is carried out,according to car-15,class II highway and class I highway were gradually loading.Finally,the experimental values of the strain and deflection of bridge structures are compared with the theoretical values.The main conclusions are as follows:Under the test load,the measured values of the stress and deflection points of each control section are less than the theoretical value,and the coefficient of stress and deflection can meet the specification requirements???1.0?,structural bearing capacity and stiffness meet the design strength requirements.After unloading,the displacement relative to the residual displacement and deflection relative to the residual displacement meet the specification requirements?S_p^'?20%?,In the static load test,according to the data analysis,the stress distribution of the box girder section satisfies the assumption of plane section,which indicates that the structure has good elastic working state.During the whole loading process,it is found that both the crack expansion and the new cracks appear,which indicates that the structure has good crack resistance.