Research On The Fire Resistance Of Concrete-Filled Steel Tubular Column And Steel Beam Composite Frame

It is of great significance to study the structural response of high-rise building in fire because of its complicated structure,high building height and many combustibles.In this paper,a high-rise concrete filled steel tubular(CFST)building is used as the research object.First of all,the fire power software FDS is adopted to simulate the indoor fire temperature field of different fire source positions,and the distribution of the indoor temperature field in different fire scenarios is obtained,and the most unfavorable fire scene is determined.In order to study the mechanical response of high-rise CFST frame structure at different positions,the finite element analysis software ABAQUS is used to verify On the basis of the validity of the finite element model,the thermal-mechanical coupling of the frame under the FDS simulated fire temperature curve and the ISO-834 standard heating curve is compared and analyzed.The deformation of the structure as a whole and the temperature field,joint deformation,stress condition and failure mechanism of each member under two temperature curves are studied,and the influence of the presence or absence of fire protection layer and the thickness of fire protection layer on the temperature field of the structure is also studied.The results show that when the fire source is in the center of the room,it is the most unfavorable fire scene.Under this scene,the maximum indoor temperature is 1019 ?,and the overall indoor temperature is above 300 ? for the longest time,for a total of 20 minutes.For CFST frame beams,the analysis of column temperature field shows that the temperature field of three-face heated CFST column is only uniaxisymmetric in the direction of vertical backfire surface,and the temperature field of four-face heated column is double-asymmetric along the section.The temperature of the upper flange is the lowest,and the temperature of the web and the lower flange is close.The analysis of failure modes of CFST frames under fire in different areas shows that two kinds of fire temperatures are not considered without considering the fire protective layer.Under the action of degree curve,the damage of the structure is the failure of steel beam,in which the damage degree of the bottom area ? is the smallest,and the failure degree of the top area III is the largest.Under the simulated fire temperature curve of FDS,all three regions of the structure do not reach the fire resistance limit,which is caused by the cooling decline stage in the whole process of FDS simulation fire development,and under the action of ISO-834 standard heating curve.The three regions of the structure reach the fire resistance limit,among which the fire resistance limit of the third region is the shortest,which is 13 min,and the fire resistance limit of the ? region is the longest,which is 29 min.Under the two temperature curves,the beam-column node area is guided by the difference of linear stiffness ratio of each member.The difference of vertical displacement in the three fire areas is not significant,but the difference of horizontal displacement is obvious.From the stress analysis,it can be seen that the upper flange of the steel beam is the weakest position of the force,for the three-face heated CFST column,the compression stress on the fire surface,the tensile stress on the back fire surface,and the longitudinal stress of the core concrete are mainly caused by expansion.For the four-face heated CFST column,the expansive tensile stress of the core concrete decreases in the cooling stage.The existence of fire protection layer can make the temperature field of the component more uniform and greatly reduce the cross section temperature of the component.With the increase of the thickness of the fire protection layer,the temperature decreases.