The Axial Ultimate Bearing Capacity Of FRP Tubed Short Concrete Columns

With the development of the building structure in our country, Fiber reinforcedpolymer(FRP) is researched and implemented comprehensively. It can be used to strengthenexisting concrete structures because of the advantages of light weight, high strength and easyapplication, and new FRP tubed concrete structure consisted of FRP tube and concrete isexpected to substitute for the concrete-filled steel tubular composite structure developingrapidly in recent years in some special areas. The FRP composites of Carbon fiber reinforcedpolymer(CFRP) and Glass fiber reinforced polymer(GFRP) involved in FRP materials havebeen applied more widely. The research of CFRP is relatively maturer than the research ofGFRP whose proposed types of member are mainly GFRP tubed columns filled withsteel-reinforced concrete and FRP-concrete-steel double-skin tubular columns and which islack of corresponding theory research. Based on the twin shear unified strength theory, theresearches on the axial bearing capacity of these two types of components were carried out.The calculation results in this paper were compared with the experiment results in relevantdocuments, and obtained some preferable results. The main contents of these results includefollowing few aspects.Under the twin shear unified strength theory, analyzing the double confinement effect ofstirrup and GFRP tube on the core-concrete, the enhancing role of longitudinal reinforcementin improving the bearing capacity of the short column is equivalent to the improvement ofconcrete strength. Considering the stress changes of concrete and steel under three-directionalpressure condition, the formula on the axial ultimate bearing capacities of GFRP tubed shortcolumns filled with steel-reinforced concrete was proposed. On the basis of it, formulas on theaxial ultimate bearing capacities of two kinds of cross section shapes of short columns, onewith no longitudinal reinforcement and the other with no steel skeleton, were carried out.Considering the restriction effect of the outer FRP tube and inner steel tube on the concreteand using the theory of thick-wall cylinder, bearing capacity of the core concrete whosecompressive strength is improved was deduced. Afterwards, formula of axial bearing capacityof FPR-concrete-steel double-skin tubular short columns was presented. By the comparisonbetween the results calculated by the formulas and the test results, it shows a good accordancewhich suggests that inferred formulas in this paper has a certain correctness and feasibility.Accordingly, using the unified strength theory will make results more accurate. On the basisof these works, several factors which may have effects on the bearing capacities are analyzed,such as the yield strength in tension and compression, the tube thickness t, the reinforcement ratio s, the material strength parameters b, the ratio of thickness and radiusof steel tubest2d eand the concrete strengthf c.In this paper, the stress versus strain relationship curves and stress contours of GFRPtubed columns filled with steel-reinforced concrete and FRP-concrete-steel double-skintubular columns were obtained using the commercial finite element software ANSYS. On theassumption that there is no relative slippage among FRP tube, concrete and steel tube, theultimate bearing capacities of these two forms of columns were simulated and compared withthe test results, and the main influencing factors were analyzed.