| With the continuous advancement of urbanization in China,the number and scale of infrastructure construction are increasing.Multi-storey buildings can’t meet the development needs of cities,so high-rise buildings have gradually become the mainstream architectural form.Because the traditional cast-in-place concrete(RC)shear wall has some disadvantages,such as long construction period,heavy pollution,self-weight of the structure and poor seismic performance,which can’t meet the current building requirements,the steel-concrete composite shear wall has been widely studied and applied.As one of the main vertical load-bearing components of building structure,the steel-concrete composite shear wall has been studied by domestic and foreign researchers.However,there are some unsolved problems in the current steel-concrete composite shear wall structure.For the steel-concrete composite shear wall,the structural measures are complicated and the degree of industrialization is low.For the single steel plate-concrete composite shear wall,the constraint effect of steel plate on concrete is weak and the construction is complicated.For the double steel plate-concrete composite shear wall,the exposed double steel plates are prone to local buckling,and the cost of fire prevention and corrosion protection is high.In view of this,the assembled steel-reinforced concrete composite tube shear wall(SRCCT shear wall)proposed by the research group is referred to as the assembled SRCCT shear wall for short.The assembled SRCCT shear wall is composed of SRCCT prefabricated in the factory and concrete poured on site.Prefabricated SRCCT consists of U-shaped steel,steel plates,bolts and tendons,and concrete outside the tube,which has the advantages of good seismic performance,light weight,convenient transportation and installation,etc.The research group has conducted relevant research on the axial compression performance of assembled SRCCT shear walls.However,the bearing capacity of SRCCT shear wall under axial compression has not been fully revealed,and the relevant comparative analysis between assembled SRCCT shear wall and cast-in-place RC shear wall has not indicated that the proposed numerical analysis method of assembled SRCCT shear wall has not been parameterized by the distance-thickness ratio,the arrangement of tie bars and the height-thickness ratio,and the design suggested value range of key parameters has not been put forward.At present,the theoretical calculation method of SRCCT shear wall axial compression performance has not considered the constraint effect of concrete outside the tube on steel tube and the buckling effect of double steel plates,so it can not be well applied to the design of SRCCT shear wall.Based on this,the main research contents and results of this paper are as follows:(1)Completed the axial compression performance test of assembled SRCCT shear wall,and revealed the stress mechanism and failure mode of SRCCT shear wall.The axial compression performance of 16 fabricated SRCCT shear walls and 2 cast-in-place reinforced concrete(RC)shear walls were tested and studied.The mechanical properties of SRCCT shear walls and RC shear walls under axial load were compared and analyzed.The experimental phenomena and failure modes of each specimen were observed and analyzed,and the influence of key parameters on the axial compression performance of fabricated SRCCT shear walls was studied.The results show that when the assembled SRCCT shear wall is subjected to vertical force,the welded rectangular steel tube and the concrete inside and outside the tube are stressed and deformed together,and the buckling of the double steel plates is restrained by bolting tendons and the concrete inside and outside the tube.The initial stiffness and bearing capacity of SRCCT shear wall are higher than those of cast-in-place RC shear wall,and the ductility is increased by about 30%.Distance-thickness ratio(the ratio of the distance between bolts and tendons to the thickness of steel plates)is the key factor affecting the axial compression performance of SRCCT shear walls.The smaller the distance-thickness ratio,the greater the initial crack load and peak bearing capacity,and the less buckling of double steel plates,the better the bearing capacity.The bearing capacity and stiffness of SRCCT shear wall are inversely proportional to the height-thickness ratio,and the axial compression bearing capacity and stiffness of the specimens can be improved by arranging the bolts in staggered rows and strengthening the side anchors.(2)Based on the axial compression performance test,the finite element model of assembled SRCCT shear wall is established and the parametric analysis is carried out,which further reveals the stress mechanism of SRCCT shear wall.The finite element simulation method is used for numerical analysis of SRCCT shear wall,and the simulation results are in good agreement with the experimental results.At the initial stage of loading,the slope of the stress-strain curve of steel and concrete is basically unchanged,the axial compression stiffness of steel and concrete is relatively stable,the bearing capacity of the specimen rises steadily,and the synergistic effect is good.Before the steel reaches the yield strain,the slope of the stress-strain curve of steel and concrete begins to decrease,the stiffness of the model begins to decrease,and the growth rate of bearing capacity slows down.Before the concrete reaches the ultimate compressive strain,the steel yields first.When the steel is in the plastic stage,the concrete reaches the ultimate stress,and the bearing capacity reaches the peak value.Both steel and concrete give full play to the expected role.The buckling shape of double steel plates can be simulated by the buckling analysis method.The thickness of steel plate,pitch-thickness ratio,pitch and height-thickness ratio have great influence on the bearing capacity of SRCCT shear wall under axial compression.Based on the consideration of peak bearing capacity and ductility,it is suggested that the thickness of steel plate should be 1-5mm,the pitch and thickness ratio should be 80-200 mm,and the pitch-thickness ratio should be 30-140.The arrangement form of bolts can be selected according to the design requirements.With the increase of height-thickness ratio of SRCCT shear wall,its peak bearing capacity will decrease.When the height-thickness ratio is less than or equal to 8,the ductility of SRCCT shear wall is directly proportional to the height-thickness ratio;When the height ratio is greater than 8,the ductility of SRCCT shear wall decreases.By analyzing the influence of different components on the axial compression performance of SRCCT shear wall,it is found that the bolt and brace can improve the peak bearing capacity of rectangular steel composite pipe and slow down the out-of-plane deformation of double steel plates.The concrete outside the tube can be stressed together with the rectangular steel tube,which constrains the rectangular steel composite tube and improves the bearing capacity.In SRCCT shear wall,the combination effect of bolt and tie bars,rectangular steel composite pipe and concrete inside and outside the pipe is better.(3)Based on the "superposition method",the theoretical calculation method of SRCCT shear wall considering the constraint effect of concrete outside the tube on steel tube,the buckling effect of double steel plates and the comprehensive constraint effect of steel tube and tie bars on concrete inside the tube is put forward.Based on the "stiffness superposition method",a method for calculating the initial stiffness of assembled SRCCT shear walls under axial compression is proposed,and the error between the calculated results and the experimental values is less than 9%.Based on the "thin-walled cylinder theory" and the "superposition method",a calculation method of SRCCT shear wall bearing capacity under axial compression is proposed,which takes into account the constraint effect of concrete outside the tube on steel tubes,the buckling effect of double steel plates and the comprehensive constraint effect of steel tubes and tied tendons on concrete inside the tube.The error is less than 10%,and the calculation result is safe.Compared with the calculation methods of axial bearing capacity suggested by mainstream codes at home and abroad,the average calculation error is 7.44% and 11.95% lower than that of Chinese standard and European standard,and the standard deviation of theoretical calculation is 28.21% and 34.59%lower than that of Chinese standard and European standard,respectively.The coefficient of variation is small and the calculation results are relatively stable,so it can be well applied to the calculation of axial bearing capacity of SRCCT shear walls.Through the axial compression test,numerical simulation analysis and theoretical calculation method analysis of assembled SRCCT shear wall specimens,this paper reveals the mechanism of axial compression and failure mode of SRCCT shear wall structure,and expounds the superiority of SRCCT shear wall over RC shear wall.The influence of key parameters on the axial compression performance of SRCCT shear wall is analyzed,and the recommended value range of key parameters is put forward through experiment and numerical analysis.Based on the "superposition method",the theoretical calculation method of axial compression stiffness and axial compression bearing capacity of assembled SRCCT shear walls is put forward,which can provide reference for the follow-up research of assembled SRCCT shear walls,and provide basis for the popularization and application of structures. |
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