Behavior of hybrid FRP-concrete-steel double-skin tubular columns subjected to eccentric compression

Hybrid FRP-concrete-steel double-skin tubular columns (DSTCs) are a new form of hybrid columns recently proposed by the third author. The new column consists of an inner steel tube and an outer FRP tube, with the space between them filled with concrete. The new column possesses many advantages over existing columns including its good ductility, corrosion resistance and ease for construction. This paper presents the results of an experimental study on the behavior of the new hybrid DSTCs subject to eccentric compression as well as results from a corresponding theoretical model using the fiber element approach. A so-called "variable confinement model" was adopted in the theoretical analysis for the concrete in the hybrid DSTCs, to account for the effect of strain gradient on the confinement effectiveness. The theoretical model was shown to provide accurate predictions of the test results, and was used in a subsequent parametric study.