Studies On Hysteretic Behavior Of Variable Section CFST Lattice Columns With Flat Lacing Tube

The variable section concrete-filled steel tubular laced column are made up of concrete-filled steel tube columns and hollow steel tubes.The size of the sections increases gradually from top to bottom.The structure has the advantages of good overall stability,high pressure-bearing capacity and structural rigidity,high ductility,attractive appearance and it can save material.Meanwhile,it can lighten the weight of building.This structure has been used in some bridges in the western mountains.Some scholars have studied the static performance of this kind of structure,but the study in the field of aseismicity is not enough.Therefore,in this paper,variable-section concrete filled steel tubular laced columns with flat lacing tube is the object of the research.Quasi-static test and finite element numerical analysis are carried out.The main work and main conclusions are as follows:(1)Quasi static test of concrete-filled steel tubular laced column with variable cross section was carried out with experimental parameters including column slope,the spacing of the tubes and axial compression ratio.The failure mechanism and failure modes of this kind of structure are studied by experiments.The influence of column slope,he spacing of the tubes and axial compression ratio on the hysteretic behavior of the structure is also analyzed.The following conclusions can be obtained through experiments:Under horizontal repeated load,the local buckling of the steel of plastic hinge region at the bottom of column limb of variable section concrete filled steel tubular laced columns with flat lacing tube occurred.The connecting area between the tube and the column limb in the middle part of the specimen are weak parts.A certain number of lacing tube were broken.The hysteretic curves of variable-section concrete filled steel tubular laced columns with flat lacing tube are plump.This structure has adequate ductility and the seismic behavior of this kind of frame is good.Increasing the column slope and reducing the vertical spacing of the tube can improve the bearing capacity of the specimen,but the structural ductility decreased.The increase of axial compression ratio will decrease the bearing capacity and ductility.(2)The finite element model of variable section concrete filled steel tubular laced columns with flat lacing tube is established by using OpenSEES software.After comparison with the test results,the influence of column slope,axial compression ratio,span of pipe and the length of specimen on the hysteretic behavior of variable section concrete filled steel tubular laced columns with flat lacing tube is analyzed.The results show that the slope of CFST limb,the length of specimen,the spacing of the tube is an important parameter affecting the stiffness of the laced columns.The peak load and ultimate displacement of this kind of structure are affected by axial compression ratio,the length of specimen and the spacing of the tubes.(3)The skeleton curves of variable cross-section concrete-filled steel tubular columns are simulated by using the three fold line model,and simplified formulas for calculating the eigenvalues of skeleton curves of these structures are derived.The main contents include four parts:The elastic stiffness of the structure is calculated by using the equivalent cross-section lattice column.Based on the structural failure mode,the virtual load displacement principle is used to calculate the peak load.According to the statistical analysis of the data we obtain the peak displacement and the limit displacement of the formula.By comparing with the results of quasi-static test data,finite element analysis and finite element analysis of the existing laced columns.It can be seen that the accuracy of the skeleton curve obtained by the simplified calculation formula meets the engineering requirements.The simplified formula of skeleton curve proposed in this paper can be used in practical engineering.