Experimental And Theoretical Research On Mechanical Properties Of New Special-shaped Columns Composited With High-strength Grouting Material-filled Square Steel Tube

Compared with traditional frame structures and reinforced concrete shear wall structures,the column limbs of special-shaped concrete-filled steel tube(CFST)columns not only can be hidden in walls,but also provide excellent seismic performance,bearing capacity and ductility.Therefore,special-shaped CFST columns have become the focus of many researchers.However,due to the diversity of the cross-section of special-shaped CFST columns,to a certain extent,the popularization and application of shaped columns are limited.And existing codes have put forward strict requirements for the applicable height of special-shaped CFST columns structure,which restricts the development of high-rise steel structure buildings.In order to promote the standardized production of special-shaped columns and break through the limitation of specialshaped CFST columns in the application of high-rise prefabricated steel structure buildings,high-strength grouting material(HGM)was applied to square steel tube(SST)based on the National Natural Science Foundation of China(52278198)and Enterprise-Commissioned Project(HX2021-01)in this paper.The new L-shaped,T-shaped and cross-shaped specialshaped columns composited with HGM-filled SST was formed for the first time.Through experimental research,numerical simulation and theoretical analysis,the mechanical properties of new special-shaped columns composited with HGM-filled SST were studied comprehensively and thoroughly.The calculation methods of axial compression and eccentric compression bearing capacities of the new special-shaped columns were proposed.The main research contents and results of this paper are as follows:(1)The progresses of research on special-shaped CFST columns and special-shaped columns composited with CFST were reviewed and the shortcomings of existing research were pointed out.And the characteristics,physical and mechanical properties and application of grouting material were reviewed.(2)Experimental studies for the mechanical properties of HGM were conducted,and the conversion relationship between the mechanical indexes of HGM was established.Axial compression tests were conducted on eight HGM-filled SST columns(HGMFSST columns),which proved that the SSTs in members have good synergistic working ability with HGM.The bearing capacity of HGMFSST columns under axial compression was calculated according to the existing codes in China and abroad.The results showed that the bearing capacity calculated by CECS 159: 2004 was closer to the test bearing capacity.(3)The mechanical properties of special-shaped columns composited with HGMFSST,including 8 L-shaped,4 T-shaped and 4 cross-shaped members,were investigated by axial compression tests.The failure pattern,ultimate bearing capacity,axial load-vertical displacement curve,strength,ductility and strain development curve of the composite specialshaped columns were comprehensively analyzed.The test results showed that the specialshaped columns,with steel tube wall thickness of 4 mm and no HGM poured inside,basically exhibited local buckling failure.The increase of steel tube wall thickness,pouring of HGM and change of section form can change the failure pattern of members.Among the members with three cross-section forms,the strength index of the cross-shaped member was relatively the highest.The strain development curves of members showed that the strength of SST was fully utilized,and SST had a good restraining effect on the internal HGM.(4)The mechanical properties of twelve L-shaped and nine T-shaped HGMFSST composite columns under eccentric compression were studied,and the failure patterns were observed.The test results showed that the composite special-shaped columns exhibited damage characteristics of overall bending.The welds between the steel tubes of special-shaped columns did not crack,indicating that the steel tubes had good cooperative working ability.The development curves of overall horizontal deflection of the special-shaped column were basically close to sine half-wave curve.At the initial stage of loading,the composite specialshaped column is in the state of full-section compression.And the variation of longitudinal and transverse strains at the middle section of members along section height was basically in accordance with assumption of flat section.(5)The numerical simulations and analyses of HGMFSST columns under axial compression and special-shaped columns composited with HGMFSST under axial compression and eccentric compression were carried out using the finite element software ABAQUS,respectively.And the simulation results were verified with the experimental results.Based on verified numerical model,the damage mechanism of the special-shaped columns under axial and eccentric compression is revealed,and a large number of parametric analyses of the factors affecting mechanical properties of the special-shaped columns were carried out.(6)The simulation analysis of 110 special-shaped columns composited with HGMFSST with constraint effect coefficients ranging from 0.3 to 5.0 was carried out by ABAQUS.And based on the unified theory and superposition theory of existing codes,the axial compression strength bearing capacity calculation method of composite special-shaped short columns was proposed.Then the axial compression stability bearing capacity calculation method of composite special-shaped columns was obtained by numerical simulation of 644 members with different slenderness ratios.(7)Based on the axial compression bearing capacity calculation method of composite special-shaped columns and further numerical simulation,the calculation methods for eccentric compression bearing capacity of L-shaped and T-shaped columns were proposed.