| Concrete-filled steel tubularcolumns with reinforcing lattice angle,is a composite component,which is formed by embedding steel skeletons(angle steel)and stiffeners in concrete-filled steel tube components,and connecting the steel skeletons with gusset plates.Compared with steel reinforced concrete components,the outer steel tube of this composite component can effectively restrain the radial deformation of the core concrete,putting concrete in a complex stress state under triaxial compression,greatly improving the compression bearing capacity of the component,and improving the ductility of the test piece.Due to the existence of the reinforcing lattice angle,the restraint effect on the core concrete is enhanced,and the crack development of the core concrete is effectively delayed and suppressed,thereby improving the compression load capacity of the component,which is different from the concrete-filled steel tubular members.On the basis of experimental research,combined with finite element numerical simulation and theoretical analysis,this paper studies the mechanical properties of concrete-filled steel tubularcolumns with reinforcing lattice angle under axial compression,and proposes a method for calculating the axial bearing capacity and stiffness of concrete-filled steel tubularcolumns with reinforcing lattice angle.The main contents are listed as follows:(1)Axial compression tests were performed on 4 groups of 8 concrete-filled steel tubular members with different internal structural forms.The load-bearing capacity,force mechanism and damage mechanism of concrete-filled steel tubularcolumns with reinforcing lattice angle and ordinary concrete filled steel tube under axial pressure was compared and analyzed.The results show that the deformation mechanism and failure mechanism of concrete-filled steel tube members with different internal structural forms are largely consistent.Each group of specimens has different degrees of bending deformation,the middle and lower portions of the outer steel tube have different degrees of bulging deformation.Changing the internal structure of concrete-filled steel tube specimens can significantly improve its ultimate bearing capacity under axial compression.Compared with the test piece without any internal stiffening measures,the bearing capacity of the test piece with internal longitudinal stiffeners was increased by4.65%;the bearing capacity of the test piece with internal steel lattice reinforcement was increased by 10.53%;the bearing capacity of the test piece with internal steel lattice reinforcement and longitudinal stiffeners was increased by 21.12%.(2)The test specimens were simulated by ABAQUS 6.14.By comparing the failure morphology and load-displacement curve obtained from the test and finite element analysis,the finite element results are in good agreement with the test,the rationality and accuracy of finite element simulation are verified.On this basis,the stress development process of concrete-filled steel tubularcolumns with reinforcing lattice angle was analyzed,and the stress mechanism and the failure mechanism are were clarified.(3)The influences of the concrete strength,steel tube strength,length to diameter ratio,steel tube diameter-thickness ratio,lattice steel size,lattice steel strength,spacing between lattice steel limbs and other parameters on the axial compression performance of concrete-filled steel tubularcolumns with reinforcing lattice angle were studied.The results show that with the increase of the core concrete strength grade,the bearing capacity of the component increases significantly,but the overall ductility of the specimen is relatively poor when the concrete is high-strength concrete;with the increase of the strength grade of the outer steel pipe,the initial stiffness of the members is basically unchanged,and the ultimate bearing capacity is increasing,but its growth rate is slowing down;with the length-diameter ratio of the member increases,the member gradually changes from strength failure to stable failure,its ultimate bearing capacity decreases significantly,and its ductility deteriorates;when the diameter-to-thickness ratio of steel pipes is 57 ～ 80,as the diameter-to-thickness ratio of steel pipes increases,the decrease in ultimate bearing capacity is smaller and the ductility is relatively worse;when the diameter-to-thickness ratio is 80 ～ 100,as the diameter-to-thickness ratio of steel pipes increases,the decrease of the ultimate bearing capacity of the component is large;the increase in the size of the internally-matched lattice steel can increase the bearing capacity and improve the ductility of the component;the increase of the strength grade of the lattice steel frame has less influence on the bearing capacity and ductility of the component;when the ratio between the spacing of steel limbs and the diameter of the members is0.438～0.563,the ultimate bearing capacity of the component increases slightly with the increase of the ratio,and the component has good ductility.(4)Based on the calculation methods of concrete-filled steel tubular members in current domestic and foreign codes,and combined with the experimental research and finite element analysis,the calculation of the axial bearing capacity and combined stiffness of the concrete-filled steel tubularcolumns with reinforcing lattice angle is proposed,the calculated results are in good agreement with the experimental results. |
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