Design Method Of FRP-Concrete-Steel Double-Skin Tubular Columns

Fiber reinforced polymer (FRP) have drawn more and more attention of the researchers in and abroad because of the advantages such as high strength-to-weight ratio and good corrosion resistance. FRP-concrete-steel double-skin tubular column (DSTC) is a new kind of hybrid column which make full use of the features of FRP. This paper has systematically investigated the design method of compression capacity of DSTC.Firstly, Tests of slender DSTC subjected to eccentric load is implemented to study the effect of load eccentricity, slenderness ratio and diameter to thickness ratio of FRP tube on the performance of DSTC. Besides the test of DSTC, the GFRP tube, seamless steel pipe and self-compacting concrete are also tested on the mechanical properties. The failure modes of FRP tube, concrete and steel pipe in DSTC under eccentric compression are also discussed.Next, numerical analysis of DSTC is conducted by the means of fiber element method combined with numerical integration. Variable confinement model of concrete is adopted to take account of impact of the load eccentricity on the confinement. A more simper analytical method of similar accuracy is proposed. The results of numerical analysis proved to be accurate enough comparing to the tests when analyzing DSTCs of different slenderness ratios and eccentricities.Then fiber element method is carried out on the compression capacity of short DSTC. The stress profile of confined concrete is simplified using an equivalent stress block, and the approximate expressions of steel tube and FRP tube are derived. Design equations for short DSTC are presented in the end of chapter.And then the computer program of slender DSTC is modified to calculate the slenderness limit for short DSTC. Parametric analysis is carried out on the parameters which may associate with that value, and five of them are absorbed into the simplified formula to calculate the slenderness limit.Finally, the compression capacity of slender DSTC is studied in detail. The economical dosage of FRP is recommended firstly and simplified equations for slender DSTC are proposed by means of nominal curvature method. All of the above design equations are shown to be accurate and reliable.