Finite Element Analysis On FRP-Concrete-Steel-Concrete Double-Skin Tubular Hybrid Columns Under Axial Compression

In recent years, the developing of Fiber Reinforced Polymer (called FRP) provides more possibilities to civil engineering. A new form of composite column, FRP-concrete-steel double-skin tubular column (DSTC) was proposed by Prof. Teng in Hong Kong Polytechnic University. In recent decade year, researches on DSTC have achieved fruitful results in aspects like the axial compression behavior, flexile performance, the analysis-oriented and design-oriented model of concrete confined by FRP, etc, which have been applied in project item.However, considering that DSTC has limit concrete area for bearing, and the steel tube may buckling inward due to its hollow interior, the low bearing capacity and poor corrosion resistance may limit it much, when works as the most important bearing carrier of some large-scale structures, especially the bridge column in the marine environment. In this paper, the study object is based on DSTC. Precast a multiple tube using the FRP tube, concrete and steel tube firstly, then pour concrete into it to form the FRP-concrete-steel-concrete double-skin tubular hybrid column, in which the constraint of multiple tube and the high durability of FRP can be take advantage of. This paper has made some finite-element analyses on the axial compression behavior of FRP-concrete-steel-concrete double-skin tubular hybrid column by using the ABAQUS software, the main contents are as follows:(1) A modified Hognestad formula was proposed to describe the stress-strain relations of concrete under uniaxial compression in ABAQUS, and the comparison with tests verify its applicability.(2) The influence on the hybrid column’s behavior caused by the change of steel tube’s location was analyzed under full-sectional loading condition. It shows that when the cross section area of steel tube remains the same, the variation of its diameter from small to large has no influence on the bearing capacity and axial deformation, but the stress distribution of concrete on cross section.(3) By researching on the constraint capacity of the multiple tube under the core loading condition, we come to a conclusion that it has different effects when the thickness of each material changes. The property of steel tube influences the first portion of the average stress-strain curve of core concrete, while the FRP tube and concrete influence the second one.(4) Study on the fracture location of FRP tube indicates that it has no business with other factors, but the size of the cylinder itself under axial compression. The fracture part on the column is determined by the ratio (β) of the height of column (H) to confined concrete’s diameter (D), and the specific fracture location by the value of D.