Study On The Axial Compression Behavior Of UHPC Columns With Circular Hollow Sandwich Steel Tubes

As a new form of concrete filled steel tube,hollow sandwich concrete filled steel tube not only has the advantages of the traditional concrete-filled steel tube,but also surpasses the ordinary concrete-filled steel tube in the aspects of earthquake resistance,fire resistance and so on.It affords broad prospects for development.In order to meet the needs of high bearing capacity and light weight of engineering structure high bearing capacity and light weight.The structural form of UHPC with circular hollow interlayer was put forward.Improving the ultimate bearing capacity of circular hollow sandwich concrete filled steel tube by enhancing the strength of core concrete.Through experiment and finite element simulation,the performance and applicability of circular hollow sandwich ultra-high performance concrete filled steel tube were studied and discussed,which provided an theoretical basis for its application.The experiments are as follows:(1)Replacing ordinary concrete with self-developed ultra-high performance concrete in hollow sandwich concrete filled steel tube.With void ratio and cross-section size as parameters,Eight ultra-high performance concrete specimens(CCFST-UHPC)and one solid circular steel tube ultra-high performance concrete specimen were prepared to conduct experimental research.The failure mode and ultimate bearing capacity of CCFST-UHPC under axial pressure were obtained by loading test,and the stress mechanism of CCFST-UHPC under axial pressure was analyzed.(2)The axial compression test results show that the axial compression bearing capacity of CCFST-UHPC with the same cross-sectional size is generally lower than that of solid steel tube ultra-high performance concrete specimens.As the void ratio increases,the bearing capacity decreases more.When the void ratio was between 0.5 and 0.7,the ultimate bearing capacity of CCFST-UHPC would be greatly improved with the increasing of cross-section area.When the void ratio is greater than 0.7,the ultimate bearing capacity of CCFST-UHPC with the same void ratio also increases with the increase of the cross-sectional size.However,its growth rate is low.It shows that when the void ratio is greater than 0.7,CCFST-UHPC cannot fully exert the strength of the core ultra-high performance concrete.(3)Selecting the constitutive model suitable for concrete-filled circular hollow sandwich steel tube.Among them,the constitutive relation model of core UHPC was compared with that of You-Ming,Wu and Lin-Hai,Han.Based on the test results and the simulation results of CCFST-UHPC finite element model,the constitutive model of UHPC which is suitable for this test was determined.(4)Referring to the finite element analysis method used by domestic and foreign scholars to analyze circular hollow sandwich concrete-filled steel tubular column under axial compression,the finite element analysis model used in this experiment was established to simulate the CCFST-UHPC under axial compression.At the same time,the load distribution between steel tubes and concrete was investigated,The results showed that For the specimens with small cross-section size,the advantage of high bearing capacity of UHPC can not be into fully play.For the specimens with large cross-section size(outer diameter reached 273mm),the proportion of axial compression of UHPC with interlayer was obviously increased.Therefore,UHPC has an edge in the concrete-filled hollow sandwich steel tubular members,and has great and wide application prospects.(5)Based on the experiment and finite element simulation analysis,the applicability of the calculation formulas of the ultimate bearing capacity of three circular hollow sandwich concrete filled steel tubular columns as the CCFST-UHPC column axial compression ultimate bearing capacity is compared and analyzed.It shows that the calculation formula of the bearing capacity of the concrete filled circular hollow steel tube proposed by our research group is more in line with the calculation of the ultimate bearing capacity of the CCFST-UHPC column in the experiment in this paper.