Seismic Behavior Of Cross-shaped Column Subjected To Compression,flexure,shear And Torsion Loads

The special-shaped column can effectively avoid the pillars protruding from the wall and has great advantages in improving the indoor viewing,reducing the structural weight,expanding the use space and facilitating the placement of furniture.It is favored by developers and users.At present,the promotion and application of the special-shaped column structure mainly adopts reinforced concrete.The application range of the special-shaped column structure is greatly restricted by the properties of the concrete material and the shape of the special-shaped column.To this end,the researchers propose a special-shaped column structure with steel reinforced concrete.Under the premise of making full use of the advantages of the special-shaped column section,the bearing capacity,ductility,stiffness and energy consumption of the special-shaped column structure are effectively improved,which greatly promoted the application of the special-shaped column.Domestic and foreign scholars have carried out extensive experimental research and theoretical analysis on reinforced concrete(RC)special-shaped columns and steel reinforced concrete(SRC)special-shaped columns.The limb of the special-shaped column is slender,and the center of mass and the center of stiffness are often not in the same position,which makes the special-shaped column easily affected by the torque.Especially under the action of earthquake,the special-shaped column is more likely to suffer damage with torsion characteristics.However,the seismic performance of the special-shaped column under the combined torsion is rarely reported.In order to study the seismic behavior of cross-shaped columns under composite torsional,a total of six SRC cross-shaped columns and nine SRC cross-shaped columns are designed to reversed cycle flexure-shear-torsion loading test with the constant compress.The test parameters consider the axial compression ratio,the T/M ratio and the steel distribution form.The failure process and shape,hysteresis curve,skeleton curve,characteristic point parameters,ductility,energy dissipation capacity,stiffness degradation and strength degradation are analysis detailed.The following conclusions can be drawn within the scope of the test parameters:Firstly,with the increase of the T/M ratio,the torsion failure characteristics of the cross-shaped column are more obvious,the failure pattern of specimens are bending,bend-torsion or torsion-shear failure mode.Secondly,with the increase of the T/M ratio from 0.14 to 0.21,the torsional bearing capacity increased by about 10%,the torsional deformation increased by more than 20%,the torsional ductility increased by 8%,the bending deformation decreased by 8%,and the displacement ductility decreased by 10%.Under the composite torsion,increasing the axial pressure is beneficial to improve the torsional behavior of the member,but has little effect on the bending behavior.The seismic performance of the solid-section shaped SRC cross-shaped column is generally superior to that of the hollow-type SRC cross-shaped columnThirdly,the energy dissipation of cross-shaped columns under composite torsion is mainly assumed by torsion in the early stage,and then by bending in the later stage.With the increase of displacement,the torsional energy dissipation increases rapidly at first,then decreases gradually,while the bending energy dissipation increases gradually as a wholeFourthly,the cross-shaped column has high bearing capacity and deformation capacity,and its displacement ductility,elastic angle and anti-collapse side angle meet the requirements of relevant specifications,and it shows good seismic performance in terms of energy consumption,stiffness degradation and strength degradationThe finite element analysis of the cross-shaped column under composite torsional is carried out by ABAQUS.The simulation results meet the requirements in a certain range of accuracy.Based on this,the influence of seismic performance on compression,T/M ratio,stirrup ratio,ratio of height to thickness,shear span ratio,thickness of steel web and flange are analyzedThe test data is normalized,and the calculation formula of corresponding simplified model is fitted to the skeleton curve and hysteresis loop.The bending-displacement restoring force model and the torque-torsion angle restoring force model are proposed by the corresponding hysteresis rules.The restoring force model reflects the bending restoring force characteristics and torsional restoring force characteristics of the cross-shaped column under composite torsion.Based on the theory of variable angle space truss,considered the effects of bending and shear,the design formula of torsional bearing capacity of RC cross-shaped column under composite torsion is proposed.The normalization formula of bearing capacity of RC cross-shaped column under compression-bending-shear-torsion is derived by shear force theory,after that,the normalization formula of torsional bearing capacity of RC cross-shaped column under composite torsion is proposed.On account of the calculation formula of the torsional bearing capacity of RC cross-shaped column,the superposition principle and equivalent replacement method are adopted for the solid-section shaped SRC cross-shaped column and the hollow-type SRC cross-shaped column respectively,and the formulas of torsional bearing capacity of SRC cross-shaped column are proposed.The calculation results are in good agreement with the experimental results,and the formula has reference value.