Behaviour and modelling of FRP-confined hollow and concrete-filled steel tubular columns

Hollow and concrete-filled steel tubes are widely used as columns in many structural systems and a common failure mode of such tubular columns when subjected to axial compression alone or in combination with monotonic/cyclic lateral loading is local buckling near a column end. The use of FRP jackets for the suppression of such local buckling has recently been proposed and has been proven by limited test results to possess great potential in both retrofit/strengthening and new construction. Against this background, this thesis presents a combined experimental and theoretical study aimed at the development of a good understanding of the structural behaviour of and reliable theoretical models for FRP-confined hollow steel tubes and FRP-confined concrete-filled steel tubes (CCFTs).;The first part of the PhD thesis is on FRP-confined hollow steel tubes. A series of axial compression tests is first presented which confirms the effectiveness of FRP confinement of hollow steel tubes. A finite element (FE) model for predicting the behaviour of these FRP-confined tubes is then described and verified with the test results.;An examination of the behaviour and modelling of CCFTs under monotonic and cyclic axial compression forms the next part of the thesis. The experimental work revealed that the FRP jacket was very effective in improving both the monotonic and the cyclic axial compressive behaviour of CCFTs in terms of both strength and ductility. An analysis-oriented stress-strain model was developed for CCFTs under monotonic axial compression and is shown to provide reasonably accurate predictions of the test results. A cyclic stress-strain model was proposed through revising an existing cyclic stress-strain model for FRP-confined.;The final part of the PhD thesis presents a series of large-scale tests on CCFTs subjected to combined constant axial compression and monotonic or cyclic lateral loading. The FRP jacket provided near the column end is shown to effectively delay or completely suppress local buckling failure at the end of a cantilevered CCFT. Both the flexural strength of the section and the lateral load-carrying capacity of the column can he significantly enhanced due to FRP confinement.