Study On Response Of Fire Process And Post-fire Residual Capacity Of Steel-concrete Composite Girder Bridge

According to the domestic and foreign building structure fire resistance standard and scientific research,investigation and analysis of the characteristics of bridge structure fire,reference at home and abroad existing research and application of technology,a series of studies have been completed by means of theoretical and numerical analysis based on the correctness of the finite element calculation model which is proved to be correct by fire test,including the basic principle of the steel concrete composite beam bridge structure behavior,structure temperature field distribution,fire resistance effect parameters,the calculation theory of residual flexural capacity,and so on.Main contents are:The calculation method of structure stress and deformation under different constraint conditions were obtained,which provide a very useful method for the finite element analysis.Fire tests were completed.The temperature and deformation of the main measuring points were obtained,and the process and mechanism of the failure of composite beams were further understood by observing the whole process of the experiment.In addition,the mechanical properties of the high temperature materials were tested,which provided the experimental basis for the value of the composite beams.The performance(thermal and mechanical properties)of ordinary steel and concrete materials in high temperature have been summarized.According to the characteristics of the research object,the appropriate material models are chosen for the basis of the research.The parameters analysis have been completed,including heating up curve,the thickness of the concrete slab,material properties of steel and concrete,concrete slab width,thickness of protection layer,the steel girder dimensions,the main factors were obtained for temperature field distribution of composite beam.The main influence parameters are obtained by analysis the influence I-shaped and composite box beam fire resistance(deformation)of factors:external load,concrete thickness,web height,plate thickness.Based on the research results of experiment and finite element analysis,the calculation theory of the residual bearing capacity of steel concrete composite beams in high temperature has been studied,Considering temperature field distribution and higher calculation accuracy,a simple calculation method of bearing capacity of steel-concrete composite beams is proposed.The calculation strength of concrete after high temperature is analyzed,and the reasonable parameter values are obtained.The main conclusions of this paper are as following:the fire resistance performance of steel concrete continuous beams is better than that of simply supported beams,and the fire resistance of composite beams is determined by the deformation of composite beams.The main factors that affect the temperature field distribution of the composite beam are temperature rising curve and concrete slab thickness.The external load and concrete slab thickness have significant influence on the fire resistance of composite beams,and the increase of web height can effectively improve the fire resistance of composite beams.The plastic calculation method of the residual bearing capacity of steel concrete composite beams in high temperature is presented,which has a good calculation accuracy and is simple and convenient.