| In this paper,the seismic performance of Steel-FRP Composite Bar(SFCB)-Ultra High Performance Concrete(UHPC)composite columns is investigated.UHPC has ultra-high compressive strength and toughness,which improves the load-bearing capacity and seismic performance of concrete columns;High strength and stable secondary stiffness of SFCB,which reduces the residual deformation of members after an earthquake and improves the repairability of the structure;The steel tube allows the UHPC to be pressurised in three directions,further improving the performance associated with the UHPC in the core.This paper investigates the effect of each factor on the seismic performance of steel tube-SFCBUHPC composite columns in terms of concrete strength,longitudinal bar type,reinforcement ratio,steel tube strength,axial compression ratio,volume-stirrup ratio and slenderness ratio.The method of combining experimental research with finite element numerical simulation is used to carry out the research analysis.The main research elements of this paper are as follows:(1)The single-factor controlled variable method was used to carry out low circumferential repeated loading tests on seven composite columns.The experimental study showed that:the hysteresis curves of SFCB and BFRP columns were full and bowed,with good energy dissipation capacity;the specimens all had good load bearing capacity and ductility performance;except for the steel combination column,the steel tube at the foot of each specimen buckled,and the buckling phenomenon was more obvious in the specimens with large axial pressure ratio and low steel tube strength;the strain of each material in the plastic hinge area was larger,the steel tube had a better concrete The restraint effect of the hoop reinforcement appeared to be weak,and the hoop reinforcement did not reach the yield strain,while the longitudinal reinforcement had a significant strengthening effect on the specimens in the test and produced larger strains;the coefficient of load degradation of each specimen was not lower than 0.93,and the improvement of the steel tube strength and the reinforcement rate of the longitudinal reinforcement could effectively improve the load degradation phenomenon of the same level;in addition to the low strength steel tube specimens and the specimens with high axial pressure ratio,the overall strength degradation coefficients of the remaining specimens were The initial stiffness of SFCB and BFRP composite columns is larger than that of steel composite columns;the larger the axial pressure ratio of the specimen,the larger the initial stiffness and the more obvious the image of stiffness degradation at a later stage;the higher the reinforcement ratio,the higher the initial stiffness of the specimen and the speed of stiffness degradation is not accelerated.(2)Numerical simulations of the seismic performance of the combined steel tube-SFCBUHPC composite column were carried out using ABAQUS and compared with the experimental results.It was found that the simulation results were in good agreement with the experimental results,verifying the feasibility of the finite element simulation.Using ABAQUS to simulate and analyse the seismic performance of the combined columns under the variation of each parameter,it was found through comparative analysis that the load bearing capacity of the specimens would increase with the increase in concrete strength,but the increase was not significant;the higher the concrete strength,the greater the initial stiffness and energy dissipation capacity of the specimen,but the ductility performance will be reduced;when the axial pressure ratio increases from 0.15 to 0.25,the energy dissipation capacity and initial stiffness of the specimen increases;when the axial pressure ratio reaches 0.25 or above,the ductility,load bearing capacity,stiffness and energy dissipation capacity of the specimen and other seismic performance indicators decrease with the increase of the axial pressure ratio;the higher the reinforcement ratio of SFCB,the stronger the load carrying capacity,stiffness and energy dissipation capacity of the specimen;when the reinforcement ratio is small,the ductility performance of the specimen is enhanced with the increase of the reinforcement ratio,and when the reinforcement ratio is large,increasing the reinforcement ratio has little effect on the ductility performance of the specimen;the hysteresis curve and skeleton curve of each specimen did not show any visual change when changing the volumetric hoop ratio of the specimen;with the decrease of the length to slenderness ratio,the seismic performance indexes such as load bearing capacity,ductility,stiffness and energy dissipation capacity of the specimens were increased substantially;as the strength of the tube grows,the load carrying capacity and stiffness of each specimen increases and the overall strength degradation trend changes less,but the energy dissipation capacity of the specimen decreases.(3)The data were processed using the dimensionless method by combining the experimental and numerical simulation data,and a recovery force model for the combined steel tube-SFCB-UHPC column was developed by fitting.The hysteresis curves of the five tested steel tube-SFCB-UHPC columns were calculated using the restoring force model and compared with the hysteresis curves obtained from the tests to verify the feasibility of the restoring force model. |
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