FRP-confined Concrete-filled Elliptical High-strength Steel Tubes Under Axial Compression

FRP-confined concrete-filled elliptical high-strength steel tube(CCFEST)is a high-performance component composed of high-strength elliptical hollow steel tube wrapped with CFRP by using the wet lay-up method,and then poured and vibrated concrete with it as a template.Under the external FRP constraint and the internal core concrete support,the internal and external buckling of the steel tube in the composite column can be effectively restrained,and the characteristics of the high-strength steel tube can be exerted to the maximum extent.At the same time,the internal core concrete has significantly improved its compressive performance due to the dual constraint of steel tube and FRP.Under the action of these three materials,the bearing capacity and ductility of CCFEST have been significantly improved,and it also has multiple advantages such as corrosion resistance,convenient construction,etc.The main contents of this thesis are as follows:(1)In this paper,18 FRP-confined concrete-filled elliptical high-strength steel tubes are tested under monotonic axial compression.In order to give full play to the restraint characteristics of FRP,thin-walled steel tube(thickness of 3mm)was used in this test.The main mechanical properties of composite columns,such as bearing capacity and ductility,are studied by the ratio of the number of layers of FRP and the length axis of the section.The stress-strain curve of confined concrete is obtained by deducting the bearing capacity of the inner steel tube.All the composite columns with FRP constraints were damaged by the most outer FRP fracture at the middle height,the expansion of the inner steel tube and the collapse of the bearing capacity.Similar to FRP confined concrete,the axial stress-strain curves of the specimens show bilinear characteristics;With the increase of the number of FRP layers and the increase of the restrained stiffness,the ultimate state of composite solid column concrete,such as compressive strength and ductility,has been improved.The change of section ratio of inner steel tube will have a great influence on the mechanical properties of composite columns.With the increase of section ratio(1.0 to 2.0),the bearing capacity and ultimate strain of composite columnsdecrease.(2)Based on the idea of Lam and Teng(2002)and the experimental data,the ultimate strength formula and ultimate axial strain formula of FRP-confined concrete-filled elliptical high-strength steel tubes are proposed,and the design model of confined concrete in composite columns is obtained.The new design model of composite column proposed in this paper has a high degree of agreement with the test value,and the formula is simple and easy to calculate,and has good universality,which can provide guidance for the axial compression performance design of such components.