Research On The Mechanical Properties Of Axially Loaded GFRP-Strength Concrete-Steel Double-Skin Tubular Columns

In recent years,(Fiber Reinforced Polymer, shorten as FRP) is widely concerned by the scholars at home and abroad since it was born. The most representative composite material is FRP tube. The GFRP-strength concrete-steel double-skin tubular columns are composed by the inner steel tube, the FRP tube and sandwich concrete. The new type composite components not only can provide an excellent alternative for concrete effectively subjected to corrosive environments, but also can raise the bearing capacity as a permanent formwork for the concrete, as a result, concrete-filled FRP tubes may adapt to the development of modern structures toward long-span, high rise and heavy-load. However, studies on FRP-concrete-steel double-skin tubular columns have been very limited. In this paper, based on the achievements in FRP tube filled reinforced concrete and concrete-filled double skin circular hollow sections, author used experimental, numerical and theoretical methods to study the properties of GFRP-concrete-steel double-skin tubular columns. The major contents are the following:The existed stress-strain calculated model for FRP tubes confined concrete are analyzed and compared, based on which two different model are proposed. A nonlinear analysis program of axial load is created, which take the effects of wall thickness, concrete strength, type of FRP tubes into account;Experimental research on the GFRP-strength concrete-steel double-skin tubular columns under axially loaded are carried out to investigate the mechanical properties of working feature, the effect of GFRP tube confining, ductility of the specimens. The analysis on composite column’s bearing capacity, deformation in different section combination form. According to the experiment results together with the existed strength equation of FRP tubes confined concrete, the strength model of the GFRP-concrete-steel double-skin tubular columns and the ultimate bearing capacity of the composite short columns are proposed. On the foundation of uniform theory, the formula of ultimate bearing capacities is worked out, the theory calculation coincides with test result;Based on the calculated results, the mechanical properties of the axially loaded slender composite columns are researched. The main concerns focus on the intermediate principal stress, strength-differential and slenderness ratio effect to the load bearing capacity and deformation of the specimens. In addition, on the basis of the twin shear unified strength theory, the bearing capacity of the slender composite columns is proposed;Based on finite element software ABAQUS, the whole the carrying capacity of GFRP-concrete-steel double-skin tubular columns under axial compression are analysised. Feature points from a typical load-deformation curve of cross section stress are analysised. Besides, the interaction between GFRP tube and concrete is taken into account in this paper. And compare finite element results to test results, the comparison indicates that the finite element model of the composite column proposed in this thesis is feasible for the analysis of axial compression behavior on hybrid columns.