Rectangular hybrid FRP-concrete-steel double-skin tubular columns: stub column tests

Hybrid FRP-concrete-steel double-skin tubular columns (DSTCs) are a new form of hybrid columns. The most common sectional form of hybrid DSTCs consists of a layer of concrete sandwiched between a circular inner steel tube and a circular outer FRP tube whose fibre directions are close to the hoop detection in order to provide effective confinement to the concrete. Much recent research has been conducted on circular hybrid DSTCs, which has demonstrated that the combination of the three constituent materials leads to several advantages not available with existing forms of columns. Rectangular (including square) hybrid DSTCs may be needed for practical applications, due to aesthetic and other reasons. When a column is subjected to different load levels in the two horizontal directions, rectangular columns are preferred. This paper extends the existing work on circular and square hybrid DSTCs to rectangular hybrid DSTCs which consist of a rectangular outer FRP tube and two circular inner steel tubes. Rresults from a series of stub column tests are presented and interpreted. The test results show that the concrete in these rectangular hybrid DSTCs is effectively confined by the tubes, leading to a very ductile response.