|Title:||Behaviour and modelling of FRP-confined hollow and concrete-filled steel tubular columns|
|Subject:||Hong Kong Polytechnic University -- Dissertations|
Tubular steel structures -- Testing
|Department:||Department of Civil and Structural Engineering|
|Pages:||xxxiii, 342 leaves : col. ill. ; 30 cm.|
|Abstract:||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 whose ductility is otherwise limited by the development of the elephant's foot buckling mode. A finite element (FE) model for predicting the behaviour of these FRP-confined tubes is then described and verified with the test results. The FE model was also used to explore the use of FRP jackets to strengthen thin steel cylindrical shells (e.g. tanks and silos) against local elephant's foot buckling failure at the base and the numerical results presented in the thesis indicate that the FRP jacketing technique leads to significant increases in the strength of such thin shells.|
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 presented in this part of the thesis includes three series of monotonic axial compression tests and two series of cyclic axial compression tests, where the main test parameters examined were the thickness of the steel tube and the stiffness of the FRP jacket. The test results 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, as it substantially delayed or in some cases completely suppressed local buckling in the steel tube; the behaviour of the concrete was also significantly enhanced due to the additional confinement from the FRP jacket. An analysis-oriented stress-strain model was also developed for CCFTs under monotonic axial compression. The analysis-oriented model considers explicitly interactions between the three components (i.e. concrete, steel tube and FRP jacket) in a CCFT and is shown to provide reasonably accurate predictions of the test results. A cyclic stress-strain model is then presented for the confined concrete in CCFTs. This cyclic stress-strain model was revised from an existing cyclic stress-strain model for FRP-confined concrete by incorporating the new analysis-oriented model developed in the present study for the prediction of the envelope stress-strain curve. 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. In CCFTs with a relatively thick FRP jacket, the buckling deformation may be forced by the FRP jacket to appear above the jacketed region. Both the flexural strength of the section and the lateral load-carrying capacity of the column can be significantly enhanced due to FRP confinement.
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