Full-scale Static Test And Mechanical Properties Of Tree-shaped Concrete-filled Steel Tubular Columns

The tree-shaped concrete-filled steel tubular column has the advantages of beautiful appearance,obvious reduction of structural span,reduction of cross-sectional size of members,high bearing capacity,etc.It has wide application prospects in large-span and large-space structures.In order to promote its application,this paper took the tree-shaped concrete-filled steel tubular columns of a Landscape Bridge Project as the research specimens.The full-scale axial compression test and cantilever bias test of the tree-shaped column were carried out.The finite element software ABAQUS was used to supplement the analysis of its mechanical performance.And the axial compression performance of the petal-shaped concrete-filled steel tubular columns("trunk")was studied.The main research contents and conclusions are as follows:A reaction force loading system suitable for laboratory conditions was designed for the full-scale axial compression and cantilever bias test of the tree-shaped column.The maximum load applied during the full-scale axial compression test of the tree-shaped column was 3.015 times the designed axial compression load,and the tree-shaped column was still in elastic state.The maximum load applied during the full-scale cantilever bias test of the tree column was 5578.7 kN,and the maximum bending moment at the bottom of the corresponding tree column was 5578.7 kN·m.The failure mode was a plastic hinge occurred at the root of the first-level branch.The finite element analysis showed that the failure mode of the tree-shaped column under axial compression was that the corner second branches and primary-to-secondary branch nodes failed.The failure mode under cantilever bias pressure was that the plastic hinge appeared at the root of the first branch.The local plastic deformation of the primary-to-secondary branch nodes reduced the bearing capacity of the tree-shaped column under axial and eccentric loads.The secondary branch at the corner was the weak link of the tree-shaped column.The effect of increasing the rigidity of the secondary branch at the corner was obvious.The influences of steel strength,concrete filling range and other parameters on the mechanical properties of the tree-shaped columns were analyzed.And the bearing capacity were significantly improved when the concrete was filled up to the second branch of the corner.The axial compression performance of the petal-shaped concrete-filled steel tubular short column was studied by finite element method.The influence of parameters such as cross rib,cross rib thickness,concrete strength,steel strength,and cross-section symmetry coefficient was investigated.The influence of cross rib opening on the axial compression performance was analyzed,and the formula of reduction coefficient of area opening ratio on axial compression capacity was proposed.The matching relationship between the thickness of the steel tube wall and the cross rib was studied.In this paper,the calculation results of petal-shaped CFST columns were compared with the calculation values of simple superposition bearing capacity formula and standard formula.The calculation formula of axial bearing capacity suitable for petal-shaped CFST short columns was proposed.Based on the calculation results of this paper,the nominal diameter to thickness ratio of petal-shaped CFST columns was proposed.