| Author: | Lu, Tianhui |
| Title: | Study on fiber-reinforced polymer bar connectors fully made of carbon/glass fiber composites |
| Advisors: | Su, Zhongqing (ME) Yu, Tao (CEE) |
| Degree: | Ph.D. |
| Year: | 2024 |
| Subject: | Fibrous composites Carbon fibers Glass fibers Glass fibers Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Mechanical Engineering |
| Pages: | xvii, 161 pages : color illustrations |
| Language: | English |
| Abstract: | Fiber reinforced polymer (FRP) material, with superior designability and mechanical performance, shows a great application potential in different industries. Especially after improvement of the surface quality, the unidirectional circular-section FRP bars can effectively replace the steel bar and be utilized in concrete structures, which is however hindered owing to the limited length of the FRP bar and the lack of effective and short connectors. Currently, there is a lack of exploration of the development and improvement of novel FRP connectors for real-world applications. This thesis aims to develop novel FRP connectors with enhanced connecting capacities. The design, manufacturing, testing, and modeling of tubular-, wedge and multi-wedge-shaped connectors are conducted to investigate and improve their mechanical properties. This thesis provides a guideline for development high-performance FRP connectors and reveals their excellent potential for industrial applications. A novel tubular-shaped glass fiber reinforced polymer (GFRP) connector is developed. It outstands the prevailing connectors due to the use of filament winding method, tailoring of the inner surface morphology and its smaller size. This work provides an analytical study to understand the stress state of FRP bars, bonding layer and the connector with complex lay-up. The results show that the FRP bars and connector carry tension and shear forces, while the bonding layer only carries the shear force. The tensile tests of the connectors with different internal surface qualities are conducted. The results illustrate that the connecting capacities and deformation mechanism of the connectors are greatly affected by the inner surface morphology of the connector. This is because of the different shear deformation mechanism of the bonding layer resulting from the different contact surface morphology. Compared with the smooth inner surface connectors, the threaded connectors demonstrate higher connecting capacities and smaller size potential. On the basis of understanding the tubular-shaped connectors, a full carbon/glass fiber wedge-shaped connector with shearing stress-enhanced locking capability is further developed, and proved effective to connect small diameter FRP bars. Quasi-static tension tests and numerical analysis are conducted to investigate their tensile responses and the effect of gradient modulus and wedge dimensions on the connector failure modes, respectively. The results show the deformation mechanisms and connecting capacities of the wedge-shaped connector are closely related to the wedge slope and thread width. By adjusting the threads length in the wedge, the FRP bar crushing failure induced by the stress concentration is effectively avoided. To connect the large-diameter FRP bars, the tubular- and single wedge-shaped connectors may lose their connecting effectiveness. Thereby, a novel multi-wedge-shaped connector for large-diameter FRP bars is developed in this work. The effects of key factors, including the wedge number, the wedge slope and the wedge length distribution on the tensile response of the connector are experimentally and numerically investigated. The results illustrate that the connecting capacities and deformation mechanism of the connectors are closely related to the wedge number and wedge slope distribution, respectively. The wedge length distribution has limited effects on the tensile response. Finally, the mechanical performances of the tubular GFRP connector and the multi-wedge-shaped connector are compared to verify the significance of the multi-wedge-shaped connector. It is found that compared with typical tubular FRP connectors, the multi-wedge-shaped connector not only has the favorable manufacturability and installing methods, but also shows the better connecting efficiency. Overall, this thesis presents that the desired connecting capacities and smaller size can be simultaneously achieved in the developed novel FRP bar connectors fully made of composites. The superiority of the multi-wedge-shaped connectors for connecting large-diameter FRP bars is also highlighted. Moreover, this work provides a qualitative relationship between key factors and the tensile response of the connectors, and forms a guideline for design and manufacturing high-performance FRP connectors. |
| Rights: | All rights reserved |
| Access: | open access |
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