Mechanical Behavior Of The Special-shaped Column Composed Of Concrete-filled Square Steel Tube Braced Frame System

Special-shaped column composed of concrete-filled square steel tubes(SCFST),with good seismic performance,can be hidden inside the wall,and the columns are not exposed in the room.The steel structure residential buildings using SCFST column technology have the advantages of excellent appearance,convenient construction,environmental protection and good application prospect.The SCFST column braced frame system presented in this paper is applied in high-rise residential building,which has great engineering application value and significant social economic benefit.In this paper,the seismic performance of the system,the design and calculation method of SCFST column structure and the fire resistance of SCFST column were studied.The main researches of this paper are as follows:In order to study the seismic performance of the braced frame,the pseudo-static tests were accomplished.The brace and beam destroyed successively,the structure showed reasonable damage mechanism.The hysteretic curve showed spindle.The skeleton curves declined gradually.The degradation of the strength was not apparent.With the increase of the axial compression ratio,the ductility and energy dissipation capacity decreased,and the stiffness and lateral force increased.After the cross sections of the SCFRT column were strengthened,ductility,energy dissipation capacity and lateral force increased.The deformation of the SCFRT column braced frame was consistent with the frame–shear wall structure.Under the action of earthquakes,weak rotation constraint between the columns in the SCFRT columns could be controlled within a reasonable range.The seismic performance of the structure was good.The finite element parametric analysis was performed to study the influence of the axial compression ratio,the column cross section and the stiffness of brace on the seismic behavior of the SCFST column braced frame.The phenomen and the result of the finite element analysis were in accord with the tests.Generally speaking,the seismic performance was not sensitive to the change of axial compression ratio.To strengthen the SCFRT column was beneficial to improve seismic performance and consolidate the second lines of Defense.To strengthen the brace could improve the stiffness of the structure,but we should avoid brittle damage.On the basis of experimental and numerical analysis,restoring force model was established,and it had certain guiding significance to the actual engineering design.Based on the existing structural design software,three methods were proposed to design the SCFST column structure,which had great significance on the popularization and application of this system.In the aspect of calculating the macroscopical indexs of the whole structure,the three methods were feasible and had a certain safety reserve.In the aspect of checking the column component,only the method of building section was feasible.The project of Fukang Home was the first high-rise residential buildings using SCFST technology in China.In this paper,the wind load analysis,the elastic analysis of the earthquake and the static elastic-plastic analysis under rare earthquake of the project were carried out.The results showed that the failure mechanism of the structure was reasonable,and the structure had high bearing capacity and good ductility.The fire resistance is an important subject in the steel structure engineering.The research of fire resistance performance of the SCFST column is still in the primary stage.The paper put forward the fire protection measures for SCFST column with autoclaved lightweight concrete slab of 50 mm thick,the fire resistance tests were conducted.The results satisfied the requirements of specifications.In the fire resistance tests,the axial compression deformation was small.With the increase of axial compression ratio,the compression deformation became larger and the fire resistance limit became shorter.Although the cross section of the steel tube column of the SCFST column was small,the concrete filled in it still showed certain heat absorption ability.After the column was wrapped by fireproof plates,cavities were formed between the mono columns in the SCFST column.The cavity had the function of heat insulation protection to the inner plates.The tests obtained the temperature field distribution of the SCFST column.By the end of the experiment,the temperature of the column was below 310℃.With the increasing of distance between the measured point and the fire surface,the temperature reduced.During the whole experiments,the column structure had been in a low temperature state,showing good fire resistance.Combined with related research,the paper summarized the key technologies of SCFST column braced frame engineering including column,joint,fire prevention and antiseptic properties.This paper made a statistical analysis of the construction cost of relevant projects,and put forward some suggestions for the structural optimization.The research results of this paper have direct significance to practical engineering.