The Regulation Investigation Of The Effect Of The End Stiffener On The Seismic Performance Of The Ultra-high Performance Concrete Filled High Strength Steel Tube Column

With the excellent mechanical performance,UHPC filled high strength steel tube structures is gradually being used in engineering.In addition,installing a stiffener inside the end of the concrete filled steel tube(CFST)is an effective way to improve the seismic performance of CFST.In order to investigate the seismic performance of UHPC filled high strength steel tube structure and optimize the installation of end stiffener,12 circular UHPC filled high strength steel tube columns with end stiffener and 2non-ribbed circular UHPC filled high strength steel tube columns are designed in this research,and the effects of axial compression ratio,the height of column,the diameter of column,the height,width and number of stiffener on the seismic performance of circular UHPC filled high strength steel tube columns are analyzed through static tests and finite element numerical simulations.Based on the existing research and the calculation method of the bearing capacity in the relevant code,the bending bearing capacity of circular UHPC filled high strength steel tube column with end stiffener is modified,and the horizontal bearing capacity calculation method of circular UHPC filled high strength steel tube columns with end stiffener is proposed.The main conclusions and relevant results are as follows:(1)When the non-ribbed specimen is damaged,it shows a compression bending damage with bulging at the end of the column;when the ribbed specimen is damaged,there is only a slight bulging at the end of the column,or even no significant change.(2)As the axial compression ratio increases,the horizontal ultimate bearing capacity and the ductility of the specimen decreases significantly.When the axial compression ratio exceeds 0.3,the failure modes of the specimen changes from buckling at the end of column to buckling at the end of column and above the stiffeners.(3)The results show that setting stiffeners inside the end of column can improve the stress distribution at the end of column,transforming the stress distribution from being concentrated at the end of column to being concentrated near the stiffeners and gradually moving upward along the stiffeners,effectively delaying and avoiding local buckling of the steel tubes at the end of column,significantly enhancing the restraint effect of the steel tubes on the core concrete,and fully utilizing the strength of the steel tubes and core concrete,the seismic performance of UHPC filled circular high strength steel tube columns has been significantly improved.Increasing the height,width,and number of stiffeners can further improve the stress distribution at the end of the column,make the stress distribution more uniform in the longitudinal direction of the specimen,effectively delay the local buckling of the steel tube,enhance the constraint of the steel tube on the core concrete,and significantly improve the seismic performance of the specimen.The height of the stiffening ribs is preferably set at 2 times the column diameter,the width of the stiffening ribs is preferably set at 1/4 the column diameter and the number of stiffening ribs is set in relation to the column diameter.(4)Based on the results of tests and finite element numerical analysis,the effects of axial compression ratio,the height,width,and number of stiffeners on the seismic performance of specimens are summarized.In combination with existing research and relevant specifications,a formula for calculating the horizontal bearing capacity of UHPC filled circular high strength steel tube columns with end stiffeners is proposed,and the calculation results are in good agreement with experimental data and finite element numerical analysis data,achieving the goal of quantitative control the seismic performance of UHPC filled circular high strength steel tube columns with end stiffeners.