Seismic Analysis Of The Ultra-high Performance Concrete-filled High Strength Square Steel Tubular Column With End Longitudinal Stiffener

Ultra-high performance concrete-filled high strength square steel tubular column with end longitudinal stiffener possess good mechanical properties due to the combination of high strength steel and UHPC.Longitudinal stiffener is placed inside the steel tube to improve the local buckling of the column base.As a new type of structural member,the researches on such columns mainly focus on static performance,with limited study on seismic performance.Therefore,this paper investigates the seismic performance of ultra-high performance concrete-filled high strength square steel tubular column with end longitudinal stiffener:(1)To systematically and comprehensively study their seismic performance,twelve test specimens were designed and fabricated,and analyzed by comparing with two ultra-high performance concrete-filled high strength square steel tubular column without end longitudinal stiffener under different stiffener heights,numbers and axial ratios.The effects of stiffener height,number and axial ratio on the failure modes,hysteresis curves,skeleton curves,strength degradation,stiffness degradation,energy dissipation and ductility of columns were investigated.the results indicate that setting reasonable stiffener inside the steel tube can not only improve the failure mode and delay the local buckling but also significantly enhance the bearing capacity and energy dissipation,thereby effectively improving seismic performance.(2)Based on experimental research,numerical simulation analysis was performed using the finite element software ABAQUS,and the simulation results were found to be in good agreement with the experimental results,which verifies the reliability of the finite element numerical models.Finite element analysis was conducted on parameters such as axial ratio and thickness with steel tube,and it was found that the bearing capacity gradually increases when the axial ratio is between 0.1and 0.2,while the bearing capacity and ductility drop when it exceeds 0.3.The thickness with steel tube significantly affects the bearing capacity.Finally,based on finite element extension analysis of parameters such as stiffener height,length,thickness and quantity,specific construction measures for ultra-high performance concrete-filled high strength square steel tubular column with end longitudinal stiffener are proposed.(3)The installation of stiffener can improve the section partial failure caused by local buckling of the steel tube.By introducing the buckling coefficient k and selecting the appropriate stiffener size,the local buckling performance can be improved.Finally,based on the experimental and finite element analysis results,and considering the influence of stiffener on bearing capacity,a calculation formula for the ultra-high performance concrete-filled high strength square steel tubular column was fitted,referencing previous research results.The calculated results were found to be in good agreement with the experimental results,providing reference and assistance for the seismic bearing capacity of this type of new composite column.