| Author: | Zhang, Ping |
| Title: | Seismic performance of structures equipped with innovative SMA-based resilient dampers |
| Advisors: | Yam, C. H. Michael (BRE) |
| Degree: | Ph.D. |
| Year: | 2025 |
| Department: | Department of Building and Real Estate |
| Pages: | xxiii, 212 pages : color illustrations |
| Language: | English |
| Abstract: | The challenge of limited natural resources in the face of growing human populations emphasises the pressing need for sustainable development. Recent post-earthquake investigations in civil engineering have revealed that, although conventional structures designed to current seismic standards may withstand earthquakes, the resulting damage often leads to high repair costs or the demolition of structures due to residual deformation, compromising sustainable development principles. Consequently, the need to mitigate earthquake-induced damage to structures has driven the development of high-performance resilient structures. This thesis introduces a novel resilient slip damper featuring a multistage energy-dissipation mechanism, explores its structural applications, and evaluates its effectiveness in seismic mitigation compared to previous systems. Note that the multistage energy-dissipation mechanism shows promise in balancing the requirements for significant post-yielding stiffness and energy-dissipation capacity in structures, based on a literature review. The proposed damper is called shape-memory-alloy (SMA)-based variable friction and stiffness damper (SMA-VFSD). In this damper, it combines the characteristics (i.e., superelastic effect and phase transformation) of SMAs, disc spring systems, and a variable friction mechanism and integrate them into a specific configuration. Supported by the restoring force from the disc spring systems, the proposed damper decouples the interdependence between the friction coefficient and the sloping angle of friction pairs, a phenomenon known as self-locking in previous research. This decoupling enables the multistage energy-dissipation mechanism and enhances the design flexibility for the damper. To validate the feasibility of the proposed damper following the multistage energy-dissipation capacity, a systematic investigation is needed. In this study, eight damper specimens were tested under cyclic loadings. The test results, including experimental observations, hysteretic behaviour, and energy-dissipation capacities, were discussed, and the effects of the design parameters (i.e., SMA bolt type, sloping angle of friction pairs and preload of SMA bolts) on damper performance were investigated. Based on test data, the accuracy of the developed analytical model in predicting the hysteretic responses for the SMA-VFSD was confirmed. Utilising the analytical model, further exploration was conducted to investigate the effects of an extended range of the design parameters on the damper behaviour. To provide a further understanding of the damper's performance, a detailed refined and a simplified numerical model were developed and validated against test data. The test and numerical results confirmed the feasibility of the SMA-VFSD at the damper level, and as expected, the damper demonstrated a multistage energy-dissipation mechanism. Further, an experimental programme investigating the cyclic behaviour of a one-bay and one-story braced frame equipped with the SMA-VFSD was conducted. Six frame tests were performed to study the effects of design parameters, including the preload of the SMA bolts and the sloping angle of the friction pairs, on structural behaviour. The frame test results demonstrated a multistage energy-dissipation behaviour with flag-shaped hysteretic curves at the sub-structure level, mirroring the findings from the previous damper test. This indicated that the frame's hysteretic characteristics was governed by the damper. Finally, the seismic performance of braced structures equipped with the proposed damper was numerically assessed via a structural case study. The effect of fabrication tolerances (i.e., clearance among pin connections) on structural performance was evaluated by comparing the seismic behaviour of structures with and without initial gaps in braces. In addition, utilising a self-developed calculation programme, nonlinear spectral analyses were performed on a Single Degree of Freedom (SDOF) system representing a low-to-medium structure showing multistage energy-dissipation characteristics. The analysis results demonstrated the viability of the SMA-VFSD in improving structural behaviour at the system level. |
| Rights: | All rights reserved |
| Access: | open access |
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