Behavior of Hybrid FRP-Concrete-Steel Double-Skin Tubes Subjected to Cyclic Axial Compression

This paper presents the results of an experimental study that was conducted to investigate the effects of key parameters on the compressive behavior of fiber-reinforced polymer (FRP)-concrete-steel double-skin tubular columns (FSDT). Hybrid FSDT columns have been introduced as a new form of hybrid columns. They consist of an outer tube made of FRP and inner tub made of steel, with sandwiched concrete between them. This paper investigated the effect of fiber angle and the ratio of steel tube diameter to its thickness (D_i/t_s) on the compressive behavior of FSDT columns. Six FSDT cylinders with different (D_i/t_s), in addition to two concrete filled-fiber tuber (CFFT) cylinders, were manufactured and tested under axial cyclic compression. The results of the experimental study indicate that the overall behavior of FSDT and CFFT is similar and the main difference is in the capacity load. Thecylinders with high D/t ratio achieve lower capacity than the normal capacity due to the local buckling of the steel tubes. Using the saturated fiber tube increases the axial ductility but does not give high confinement. These results are presented together with a discussion on the influence of the studied parameters on the compressive behavior of FSDTs.