Behavior of large-scale hybrid FRP-concrete-steel double-skin tubular columns under concentric compression

Hybrid fiber reinforced polymer (FRP)-concrete-steel double-skin tubular columns (hybrid DSTCs) are a novel form of columns with superior load-carrying capacity, ductility, and corrosion resistance. Such columns consist of an outer FRP tube, an inner steel tube, and the concrete filled between the two tubes. While they have attracted extensive research attention worldwide, most of the existing studies have been focused on small-scale specimens. In particular, the behavior of large-scale hybrid DSTCs with a filament-wound FRP tube and self-compacting concrete (SCC) has not been systematically investigated. Against this background, this paper presents a systematic experimental study on large-scale hybrid DSTCs under concentric compression with the following important issues being particularly investigated: the use of large-scale specimens, the use of prefabricated filament-wound FRP tubes compared with wet-layup FRP tubes, and the effect of shrinkage of SCC. The test results confirmed the excellent ductility of hybrid DSTCs and revealed that the types of concrete (SCC versus normal concrete) and FRP tube (wet-layup versus filament-wound tubes) significantly affected the compressive behavior of hybrid DSTCs. Finally, the predictions of an existing design-oriented stress-strain model for confined concrete in hybrid DSTCs, which was developed based on test results of small-scale hybrid DSTCs made with normal concrete and confined with a wet-layup FRP tube, are compared with the test results. It is shown that the model provides reasonably accurate predictions for confined concrete in the large-scale hybrid DSTCs with a typically bilinear shape, but it fails to predict the obvious axial stress drop after the first peak load caused by the large shrinkage of SCC.