|Title:||Hybrid FRP-concrete-steel double-skin tubular columns under static and cyclic loading|
|Subject:||Tubular steel structures|
Columns, Iron and steel
Hong Kong Polytechnic University -- Dissertations
|Department:||Department of Civil and Environmental Engineering|
|Pages:||xxxi, 306 pages : color illustrations ; 30 cm|
|Abstract:||This thesis presents a systematic study on the structural behavior of hybrid FRP-concrete-steel double-skin tubular columns (hybrid DSTCs) under static and cyclic loading, with particular attention to the use of high strength concrete (HSC) and the effect of column size. A hybrid DSTC consists of a layer of concrete sandwiched between an outer tube made of FRP and an inner tube made of steel. The FRP tube, with fibers oriented close to the hoop direction, is used to confine the concrete and to enhance the shear resistance of the column. This column form was proposed by Prof. J.G. Teng to achieve excellent durability and ductility (and hence seismic resistance). Following the introductory and the literature review chapters of the thesis, Chapters 3 and 4 present the first part of the research program concerned with the behavior of concrete filled FRP tubes (CFFTs) under cyclic axial compression. The experimental work included the concrete strength as a key variable, and was designed to supplement the very limited existing research on the cyclic compressive behavior of FRP-confined HSC. Lam and Teng's cyclic stress-strain model was critically assessed using the new test results as well as existing test results. A modified version of Lam and Teng’s model, applicable to both normal strength concrete (NSC) and HSC confined with either a wet-layup FRP tube or an FRP filament-wound tube, was then proposed. The proposed model was found to provide reasonably accurate predictions of test data. Chapters 5 and 6 present the second part of the research program which was concerned with the behavior of hybrid DSTCs filled with NSC/HSC subjected to monotonic/cyclic axial compression. Previous studies on the axial compressive behavior of hybrid DSTCs were generally limited to small-scale specimens (i.e. with a diameter < 200 mm) filled with NSC and confined with a wet-layup FRP tube. The experimental investigation was thus focused on three issues: (1) the effect of using HSC; (2) the effect of using a filament-wound FRP tube; and (3) the effect of specimen size. The test results were compared with Yu et al.'s model for static behavior and the stress-strain model presented in Chapter 4 for cyclic behavior. Both models were found to provide reasonably accurate predictions of test results. Chapters 7 and 8 present the last part of the research program which was focused on the seismic behavior of hybrid DSTCs filled with NSC/HSC. A series of DSTCs were tested under combined axial compression and cyclic lateral loading. The test columns had a relatively large column section (i.e. with a diameter of 300 mm) and a realistically large void ratio (i.e. 0.73) to achieve close representation of real column behavior. The test results indicated that hybrid DSTCs possess excellent ductility and seismic resistance even when HSC with a cylinder compressive strength as high as 120 MPa is used. A numerical column model for DSTCs under combined axial compression and cyclic lateral loading was then developed, whose predictions were found to be in close agreement with the test results.|
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