Study On Axial Compression Behavior Of Cross-shaped And L-shaped Multi-cavity Self-compacting Concrete Filled Steel Tube Shear Walls

The multi-cavity concrete-filled steel tube shear wall is a composite structure formed by filling the core concrete in the multi-cavity steel tube.The core concrete improves the stiffness and local stability of the thin-walled steel tube and prevents the local buckling of the steel tube prematurely.The hoop effect of the outer steel tube on the core concrete improves the compressive strength and elastic properties of the core concrete and transforms it from brittle material to plastic material.The combined effect of multiple steel tubes and base concrete gives the member excellent structural characteristics such as high capacity,high conductivity and high dispersion capacity.As a new type of member,scholars mainly carry out experimental research on the mechanical properties of zigzag and T-shaped multi-cavity self-compacting concrete filled steel tube shear walls,there are relatively few studies on cross-shaped and L-shaped multi-cavity concrete-filled steel tube shear walls,and there are no provisions on the axial bearing capacity of Cross-shaped and L-shaped multi-cavity self-compacting concrete filled steel tube composite shear walls in the code at present.However,with the change of steel and steel yield strength and other parameters,the axial compression mechanism and bearing capacity calculation formula of cross-shaped and L-shaped multi-cavity steel tube self-compacting concrete shear walls may be different.Therefore,the axial compression performance and energy mechanics of cross-shaped and L-shaped multi-cavity self-compacting concrete filled steel tube shear walls are studied by means of experiments and finite element models in this paper.The main conclusions are as follows:(1)The optimal(SCC)mix ratio of C50 fly ash-silica fume self-compacting concrete is obtained by working performance test,compressive strength test,splitting test and conventional triaxial test,the formation mechanism of fly ash and silica fume on SCC strength is revealed by SEM microscopic analysis,and the correlation models shall be established between pressure strength and the relationship models between fissile tensile strength,and ultrasonic amplitude and SCC strength.The relation model of peak stress,peak strain and confining pressure of fly ash-silica fume SCC under different fly ash substitution ratio is obtained,and the Mohr-Coulomb failure criterion suitable for fly ash-silica fume SCC is modified.The axial compression tests of three Cross-shaped and three L-shaped multi-cavity self-compacting concrete filled steel tube shear walls were designed and carried out,and the failure process of multi-cavity self-compacting concrete filled steel tube shear walls was observed.the axial load-strain curve,displacement ductility coefficient and ultimate bearing capacity of the specimen are studied,and the effects of cavity number and cavity section on the ultimate bearing capacity of the specimen are analyzed.(2)Three cross shaped and L-shaped multi cavity self compacting concrete filled steel tube shear walls were designed and tested under axial compression;The influence of cavity number and cavity cross-section form on the ultimate bearing capacity of shear wall is analyzed.The axial load-strain curve,ultimate bearing capacity and displacement ductility coefficient of shear wall are studied.(3)The axial compression finite element models of Cross-shaped and L-shaped multi-cavity steel tube self-compacting concrete shear walls are established by using Abaqus FEM software.The finite element results are compared with the literature test results,and verify the accuracy of the FEM.On this basis,21 Cross-shaped and 21 L-shaped multi-cavity self-compacting concrete filled steel tube shear walls are established.The effects of concrete strength,steel thickness and steel yield strength on the axial compression behavior of multi-cavity steel tube self-compacting concrete shear wall are analyzed,and the stress mechanism of the shear wall is analyzed by the axial compression load distribution curve of typical members.(4)Based on the FEM parameter analysis and limit equilibrium theory,the formulas for calculating the bearing capacity of cross-shaped and L-shaped multi-cavity concrete filled steel tube shear walls are established,and the errors between the simplified formula and the finite element results are less than±10%.It shows that the formula has high accuracy,and It can be used as a reference for practical technology application.