Study On Hysteretic Behavior Of External Spiral Rib Stiffened Thin-walled Concrete Filled Steel Tube Columns

The thin-walled concrete filled steel tubular column is the section form of the section diameter thickness ratio of 1.5 times more than the gauge limit value.The thin-walled concrete filled steel tube is widely used in the building structures such as the middle and low level buildings and the elevated bridge pier.The local buckling is easy to occur during the use of thin-walled concrete filled steel tubular columns,which leads to the rapid degradation of bearing capacity and stiffness,especially when the seismic action is encountered,which is not conducive to the safety of the structure.In order to improve the flexion resistance of the thin-walled concrete filled steel tube and increase its seismic performance and ductility,the test proposed that the aseismic performance of the concrete is improved by the external spiral stiffening constraint.In this paper,the hysteretic behavior of concrete filled steel tubular columns and outer helical rib thin-walled concrete-filled steel tubular columns is tested.The failure modes and failure mechanisms of two kinds of columns were obtained through observation during the test.The hysteretic curves,skeleton curves,energy dissipation coefficients and ductility properties of these two kinds of columns are obtained by analyzing the test data.The test shows that the external spiral rib can increase the force range of the column from the bottom of the column to the middle of the column,and the external concrete of the external spiral thin-walled concrete filled steel tube column does not participate in the force.From the test data,it is found that the ductility and energy dissipation factor of the outer spiral rib thin walled concrete filled steel tube column are higher than that of the ordinary concrete filled steel tube.The results show that the external spiral rib improves the ductility of the column and the energy dissipation performance,and improves the aseismic capacity of the column.The numerical simulation of external helical concrete filled steel tubular columns is carried out,mainly for the number of helical ribs,width thickness ratio,pitch and other parameters.The simulation results show that the peak load of the column will increase slightly with the increase of the number of spiral ribs when the number of the spiral ribs gradually increases,but the increase of the strength will no longer be obvious when the number of the spiral ribs is more than four.In the process of increasing the width of the spiral rib,the column strength also increases,and increases obviously.It can be seen that the strength of the column is proportional to the increase of the width and thickness ratio of the spiral ribs by two.In the process of numerical simulation,when the pitch of the helical rib is changed,there is no obvious regularity with the increase of the strength of the cylinder with the increase of the pitch,but the optimal pitch makes the performance of the column aseismic performance best.It is found that the optimum spiral rib and the vertical angle of the tube wall are about 45℃～60℃.Through the study,the hysteretic behavior and seismic performance of the external spiral stiffened thin-walled concrete filled steel tubular column have some understanding,and the performance of the thin-walled concrete filled steel tube with external spiral ribs is verified by the test,and some suggestions are provided for the structure design.It lays a solid foundation for the engineering application of the new steel pipe concrete composite column..