Research On Fire Resistence Limit Of Concrete Filled Square Steel Tubular Column Protected By Ultrathin Fireproofcoating

The concrete-filled square steel tubular column has the advantages of convenient joint treatment,excellent fire resistance and convenient construction,and the material properties of steel and concrete in it can be fully utilized,so it is applied to high-rise buildings.The strength of steel declines so dramatically at high temperature due to its exposure,thus the research about the fire resistance of concrete filled steel tubular column is very important.Present domestic researches of concrete filled steel tubular column fire resistance revealed that,the fire resistance of concrete filled steel tubular column is not up to the standard requirements with plain concrete in core and without any protective measure for steel tube.Most researches so far used thick fireproof coating when fireproof coating is needed as protective layer of steel tube;but thick fireproof coating demands cumbersome construction procedures,occupies much space and badly affects the appearance.So this paper uses ultra-thin indoor steel fireproof coating.Therefore,in this paper,concrete filled square steel tubular columns and steel columns fire-resistant tests including parameters such as steel ratio,fire mode and coating type,were carried out.Parameters which influence the temperature field,such as fire mode,steel ratio,heating time,section side length,were calculated respectively;and the main influential parameters were summed up.Parameters which influence the fire resistance limit,such as steel ratio,axial compression ratio,section side length,strength of steel and concrete,were also calculated respectively;and the main influential parameters were summed up.The paper mainly includes the following parts.(1)Parameters in the tests include the fire mode(one side or two opposite sides fire),steel ratio(0.1 or 0.15)and coating type(two domestic coatings).The failure modes and the deformation development processes of the concrete filled square steel tube columns protected by ultra-thin fireproof coating subjected to one side and two opposite sides were obtained by carrying out eight full-scale plain concrete filled square steel tubular columns fire-resistant tests.Meanwhile,by carrying out four full-scale steel columns fire-resistant tests,whose parameters also include the fire mode(one side or two opposite sides fire),coating type(two domestic coatings)and steel ratio(0.1 or 0.15),the fire resistance of concrete filled steel tubular column and steel column was compared.Data of the temperature field and deformation wererecorded during the tests.(2)Selecting suitable material thermal parameters,through ABAQUS finite element analysis software,the temperature field analysis model of the experiment was established,then compared with the experimental results to verify its correctness.Meanwhile,parameters' effects on the temperature field were analyzed,including steel ratio,section side length,heating time and fire mode.(3)By collating parameters of steel and concrete under high temperature,such as thermal expansion coefficient,strength,elasticity modulus and stress-strain model,material thermodynamic parameters suited to this paper were determined.(4)On the basis of temperature field calculation,the fire resistance model was established through ABAQUS.Theoretical calculation results were compared with the experimental results.And parameters which influence the fire resistance limit were calculated,including fire mode,load ratio,section side length,steel ratio,steel and concrete strength.Main factors which influence the fire resistance limit were summed up by using the experiment results and calculation results.