| Author: | Zhao, Menghan |
| Title: | Behavior of hybrid FRP-UHSC-steel double-skin tubular columns and beams |
| Advisors: | Dong, You (CEE) Teng, Jin-guang (CEE) |
| Degree: | Ph.D. |
| Year: | 2024 |
| Subject: | High strength concrete Building, Iron and steel Reinforced concrete construction Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Civil and Environmental Engineering |
| Pages: | xxxii, 312 pages : color illustrations |
| Language: | English |
| Abstract: | Due to extensive research in the past two decades, the boundary of concrete strength has been extended beyond 150 MPa in laboratories, stepping into the realm of ultra-high strength concrete (UHSC). UHSC has great potential in creating more usable space for high-rise buildings and reducing the environmental impact of cement production. However, many issues remain unsolved before its wide practical applications, including raw material costs, poor workability, challenging mixing processes, and excessive brittleness. Sound design provisions for its structural use are not yet available due to limited research. Against this background, this PhD thesis presents a research programme on the development and use of a desirable UHSC. The research programme started with studies on the mix design and key material properties of a desirable UHSC, which was followed by studies on the behavior of hybrid fiber-reinforced polymer (FRP)-UHSC-steel double-skin tubular columns (DSTCs) and beams (DSTBs) incorporating this new UHSC. The first part of the PhD research programme, presented in Chapters 3 and 4, is concerned with the mix design of a desirable UHSC and its design-related properties. Extensive tests were carried out on numerous UHSC cubes, cylinders, and prisms to investigate the compressive strength, stress-strain relationship, flexural strength, shrinkage properties, and temperature performance. The effects of the shape, size, and shape accuracy of test specimens on the compressive strength of UHSC were experimentally investigated. Furthermore, the related design equations for the structural use of conventional concrete in the current codes of practice are examined against the test results. The second part of the PhD research programme is presented in Chapter 5, in which the compressive behavior of FRP-confined UHSC is studied. The work of this chapter serves as a prerequisite for exploring the performance of hybrid FRP-UHSC-steel DSTCs and DSTBs. Two series of axial compression tests were designed, with one focusing on small-scale wet lay-up FRP tube-/FRP wrap-confined UHSC and the other focusing on large-scale filament-wound FRP tube-confined UHSC. The test results showed that FRP confinement can enhance both the strength and ductility of UHSC significantly, shedding light on the feasibility of this research path. The existing axial stress-strain models for FRP-confined normal-/high-strength concrete are examined in this chapter against the test results, showing that these models are suitable for predicting the axial stress-strain behavior of UHSC if the FRP confinement is above a threshold level. The last part of the PhD research programme, presented in Chapters 6 and 7, is concerned with the axial compressive behavior of hybrid FRP-UHSC-steel DSTCs and flexural behavior of DSTBs. The work of these two chapters is an extension of the research to the structural level based on the material-level studies presented in the previous chapters. Fourteen DSTCs with different FRP tube thicknesses and void ratios were tested under axial compression. Six DSTBs were tested under four-point bending, with the variables being the cross-sectional configuration, FRP thickness, and fiber orientations. Both the DSTCs and DSTBs incorporating the UHSC developed in the present PhD research programme were found to possess good ductility. |
| Rights: | All rights reserved |
| Access: | open access |
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