| As a novel type of cross-section of concrete-filled steel tubular short columns,round-ended concrete-filled steel tube stub columns(RRCFST)have excellent mechanical properties such as high bearing capacity,good plasticity and toughness,and have the advantages of aesthetics,practicality and economy.They are widely used in bridge piers.At present,the research on RRCFST is increasingly deep,but they are concentrated on semi-circular members at both ends of the cross-section,and their definitions are narrower.The round-ended concrete-filled steel tubular short column generally includes a semi-arc-shaped central angle ? ? [0°,180°] at both ends,and a concrete-filled steel tube member in the middle of the rectangular section.When the central angle is 180° and the central rectangular cross-sectional area is zero,it is a round steel tube concrete.When the central angle is 0° and the central rectangular crosssectional area is not zero,it is a rectangular steel tube concrete.The round-ended concrete-filled steel tube concrete is incorporated into the circular and rectangular steel tube concrete,communicating the circular and rectangular members,which is beneficial to the deep understanding of the RRCFST.Through the axial compression test of the generalized round-end concrete-filled steel tubular stub column,the force performance is explored.The main work and research results are as follows:1.Eleven round-ended CFST stub columns were carried out under axial compression tests.The parameter variables were steel tube thickness,inner rectangular aspect ratio and central angle.Experimental results show that when the central angle is small,the failure modle is close to the rectangle,but the local buckling degree of the arc segment is smaller than that of the rectangle;when the central angle is large,the failure modle is mainly the outward local buckling of the outer steel in the middle of the straight section.The analysis of the restraint effect shows that when the aspect ratio of the middle rectangle is constant,the angle of the center of the rectangle increases.The constraint effect gradually increases and then weakens.2.The finite element simulations of 11 axial compression test stub columns were carried out,and the appropriate steel tube and concrete constitutive model,material yield criterion,element type and mesh division were selected respectively,and the contact stress between steel tube and concrete was also analyzed.The results show that the calculation results of concrete stress-strain relationship of D's are in good agreement with the experimental results;the contact effect between steel tube and concrete members is mainly reflected in the joint effect of circular arc section and arc section on core concrete.3.Based on the finite element model of the RRCFST,the parameters of the specimens with the central angle of 60° and 120° are analyzed.The ultimate bearing capacity and the restraining effect are considered throught the concrete strength,steel strength,aspect ratio and size effect.The results show that the increase of steel strength and the increase of concrete strength can effectively increase the restraint effect.With the increase of the aspect ratio and the increase of the size,the constrained effect is gradually reduced.The results of the constrained effect analysis of different crosssections under the same area show that the constraint effects of different cross-sections are different,and the overall constraint effect is not only stronger than the constraint effect.Weak correlations are also related to the constrained effect area.4.Based on the axial compression test and parameter analysis,two methods are used to propose a unified formula of ultimate bearing capacity.The results show that compared with the strong and weak constrained partition model,the unified formula of the circular end bearing capacity obtained by the equivalent rectangular model redefined by the constraint effect is more consistent with the experimental results. |
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