| Author: | Xiong, Wei |
| Title: | FRP-concrete-steel double-skin tubular columns and arches with a stiffened steel tube |
| Advisors: | Teng, Jin-guang (CEE) Yu, Tao (CEE) |
| Degree: | Ph.D. |
| Year: | 2024 |
| Subject: | Fiber-reinforced concrete Tubular steel structures Buckling (Mechanics) Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Civil and Environmental Engineering |
| Pages: | xxxi, 483 pages : color illustrations |
| Language: | English |
| Abstract: | Hybrid FRP-concrete-steel double-skin tubular columns with a stiffened steel tube (referred to as hybrid stiffened DSTCs or simply S-DSTCs) represent an enhanced form of hybrid DSTCs originally invented by Professor Jin-Guang Teng at The Hong Kong Polytechnic University (PolyU). Compared to hybrid DSTCs without stiffeners, the introduction of stiffeners: 1) substantially enhances the sectional capacity; 2) provides additional restraints against the local buckling of the steel tube; 3) enhances the composite action between the steel tube and the concrete. The sectional forms of S-DSTCs have great potential for application in arch structures due to their excellent corrosion resistance, high strength-to-weight ratios, ease of construction, etc. Arches employing a S-DSTC section are referred to as hybrid stiffened double-skin tubular arches or simply S-DSTAs. While some studies on S-DSTCs have been reported in the literature, they are far from providing a comprehensive understanding of these members. Notably, the buckling behavior of steel tubes in S-DSTCs has not been well understood. Furthermore, no study exists on the behavior of S-DSTAs. This Ph.D. thesis presents the results of a research program undertaken to fill these knowledge gaps. The thesis first presents a systematic experimental investigation into the material tensile properties, geometric imperfections, and residual stresses of stiffened steel tubes of various manufacturing methods, diameter-to-thickness ratios, stiffener shapes, and stiffener configurations. It then examines the buckling behavior of these stiffened steel tubes as observed in compression tests. The buckling modes, buckling strains, and buckling loads are analyzed in detail. Empirical equations are also proposed to predict the buckling resistance of these stiffened steel tubes. The thesis then presents an experimental investigation on the behaviors of DSTCs and S-DSTCs under concentric and eccentric compression. The effects of FRP confinement stiffness ratio, steel tube thickness, steel tube manufacturing method, stiffener shape, stiffener quantity, and load eccentricity on the compressive behavior of DSTCs and S-DSTCs are all examined. The test results demonstrate that the buckling strain of steel tubes in DSTCs or S-DSTCs can be effectively improved by FRP confinement, with the enhancement ratio of buckling strain being up to about 400%. Besides, comparisons of the test results between DSTCs and S-DSTCs exhibit the benefit of stiffeners in enhancing the buckling resistance of the inner steel tube (with the enhancement ratio of buckling strain being up to about 140%) and the confinement effect for concrete (with the improvement in the axial stress reaching about 10 MPa at the transition portion). Existing design-oriented stress-strain models for FRP-confined concrete in DSTCs are employed to predict the test results of DSTCs and S-DSTCs. Comparisons between test results and predictions reveal that incorporating steel tube buckling and stiffener confinement effects may be necessary for achieving more accurate predictions. The thesis next presents a comprehensive investigation into the analysis and design methods for DSTAs. The design method of DSTAs is illustrated through a detailed design process. Key design parameters are also discussed in detail. A comparative study is presented on the performance of a DSTA versus that of a steel tubular arch (STA) and a concrete filled steel tubular arch (CFSTA). A parametric study is then presented with an emphasis on the effects of FRP tube thickness and stiffeners on the performance of DSTAs. The results given in this chapter conclusively demonstrates the superior structural performance and design flexibility of DSTAs and S-DSTAs. |
| Rights: | All rights reserved |
| Access: | open access |
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