Behavior Of Hexagonal CFST Columns Under Eccentricial Compression

Recently,hexagonal CFST members are used in some hige-rise buildings for their high strength,good ductility,excellent workability and aesthetic performance.Up to now,CFST members have done a great deal of research,but the study of hexagonal CFST members performance is rather limited.The behaviors of hexagonal CFST members under the axial compression and eccentricial compression are investigated in this study,and the finite element(FE)soft ABAQUS was used for mechanism analysis and parameter analysis,simplified models were proposed to calculate the load-bearing capacities of the long columns and the members under eccentricial compression.The following research works were carried out:(1)For laying the foundation of the necessity and feasibility of the research,the relevant references and research were first presented.(2)The parameter of experimental work is slenderness ratio and eccentricity ratio.Tests includes 13 members are carried out on the specimens under eccentricial compression.Similar to the normal CFST column,with the increase of the slenderness ratio and eccentricity ratio,the bearing capacity of the hexagonal CFST column decreases obviously.The failure modes of hexagonal CFST columns include excessive deflection development,the steel tubular buckling,concrete crushing in the compression zone,concrete cracks in the tension zone.(3)The numerical simulation were carried out using finite element(FE)analysis software ABAQUS,the predicted results agree well with the test results.(4)The FE model is then used to conduct the mechanism analysis of these members and which includes the failure modes,the load-deformation curves and stress distributions of steel and concrete.Analysis shows that similar to normal CFST column,the load of the steel tube has reached the peak before the bearing capacity of the member reaches the peak.The constraining force of steel tube to concrete mainly focused on the corner of the cross-section.(5)Meanwhile,based on the FE model the parametric analysis for the load-deformation curve and N/Nu-M/Mu interaction curve was performed,the main parametric includes the steel ratio,steel yield strength,concrete strength,eccentricity ratio and slenderness ratio.Analysis shows,for CFST long column under axial compression,with the increasing of the steel ratio and the decreasing of the strength of concrete,the stability factor of the hexagonal CFST long columns also increases.For the beam-columns under the eccentricial compression,with the increasing of the slenderness ratio and eccentricity ratio,the bearing capacity of the beam-column is significantly reduced.For the beam-column under the eccentricial compression,with the increase of the steel ratio of the cross section and steel yield strength,the equilibrium point of the N/Nu-M/Mu interaction curve moves inward.With the increase of concrete strength,the equilibrium point of the N/Nu-M/Mu interaction curve moves outward.(6)Based on the database of the parameter analysis,the simplified model for the load-bearing capacity of hexagonal CFST long column under axial compression and the beam-columns under the eccentricial compression were proposed.The result of the simplified model agree well with the result of parameter analysis.