Research On The Mechanical Performance Of Concrete-Filled Thin-Walled Square Steel Tube With Spiral Stiffener Under Eccentric Compression Load

Concrete-filled steel tube is widely used in various fields of civil engineering due to its own advantages.However,the ordinary CFST pipe wall is so thick that the economic benefit is poor.A thin-walled concrete-filled steel tube is proposed in order to decrease the consumption of steel and reduce the construction cost.The thin-walled steel tube is prone to local buckling under load,which degrades the performance of the component.In this paper,the restraining form of spiral stiffeners is proposed in combination with rib stiffeners and spiral stirrups,in order to improve the deformability of concrete-filled square steel tubular columns and delay the degradation of mechanical properties in the plastic phase.In this paper,the eccentric compression test of 4 specimens was carried out,and on the basis of the test,ABAQUS finite element software was used to analyze the parameters of the concrete-filled thin-walled square steel tube columns with spiral and vertical reinforcement.The specific research contents and results are as follows:Firstly,the eccentric compression test of ordinary concrete-filled thin-walled square steel tube columns,concrete-filled thin-walled square steel tube columns with spiral ribs,concrete-filled thin-walled square steel tube columns with spiral ribs and vertical steel bars and concrete-filled thin-walled square steel tube columns with spiral ribs and vertical plate were carried out.Observe the test phenomenon,analyze the load-displacement relationship curve,load-deflection curve,and stress variation of each part.The results show that the local buckling of the thin-walled square steel pipe with the spiral stiffener is significantly reduced.Compared with ordinary thin-walled concrete-filled steel tubular columns,the bearing capacity of the concrete-filled thin-walled square steel column with spiral ribs and steel bars increased by 17.9%due to the fact that the addition of steel reinforcement enhances the restraint of the core concrete and enhances the bond between the outer concrete and the steel tube.And compared with the concrete-filled thin-walled square steel tube column with spiral,the deflection under the ultimate load increased by 33.3%,and the deformation capacity was greatly improved.On the basis of the experiment,the nonlinear finite element method was used to simulatethe concrete-filled thin-walled square steel tube columns with spiral ribs and vertical steel bars.and the test results were compared with the finite element calculation results.The research shows that the results of finite element analysis agree well with the test results,the error of load value is within 10%,and the trend of stiffness degradation is similar,which verify the reliability of finite element calculation and can be used as a basis for multi-parameter extension analysis.By changing the eccentricity of the test piece,the width-to-thickness ratio of the steel tube,the width-thickness ratio of the stiffener and diameter of vertical reinforcement bar,the concrete-filled thin-walled square steel tube columns with spiral ribs and vertical steel bars were analyzed.The results show that when the eccentricity of the test piece increases,the bearing capacity of the test piece decreases,and the ductility is improved.When the width-thickness ratio of the steel tube decreases,the bearing capacity is obviously improved,and the ductility is also improved.Reducing the width-to-thickness ratio of the stiffener has little effect on the bearing capacity of the test piece.When the diameter of the vertical reinforcing bars increases,the bearing capacity of the test piece is slightly increased and the ductility is increased.