Abstract
Improving community resilience to natural hazards such as earthquakes is one of the central challenges in the 21st century. Among others, the performance of individual buildings is a critical factor that dictates how soon societies impacted by seismic hazards could recover. Recent earthquakes have demonstrated that many buildings designed based on modern code requirements were not occupiable due to substantial structural damages, taking months or years to repair or reconstruct. Mitigating the devastating socio-economic impacts of earthquakes requires an urgent need for expanding performance goals beyond life safety to achieve rapid re-occupation and functional recovery. In that perspective, residual drifts play a significant role in determining the post-event functionality of buildings. The necessity to limit residual deformations within an acceptable threshold has urged researchers to develop self-centering structural systems that can return to their original plumb position after a seismic event. While self-centering capability in a structure can be realized in several ways, superelastic shape memory alloys (SMA) that possess inherent re-centering and energy dissipation capabilities are promising materials to develop self-centering devices.
This research proposes innovative SMA-based structural control devices that can enable re-occupancy or functional recovery of buildings after a major earthquake within a reasonable amount of time. This dissertation follows a thorough investigation starting from material-level characterization, then moving to a component-level investigation, and finally to a system-level evaluation. First, the buckling and post-buckling behavior of large-diameter superelastic SMA bars were explored. A digital image correlation measurement system and an infrared thermal imaging camera were implemented to monitor full-field strain and surface temperature fields. The interaction between material nonlinearity (due to phase transformation) and geometric nonlinearity was explored. Furthermore, the effects of strain rate on the buckling and post-buckling responses were examined. Second, the studied SMA bars were employed to develop a new damping device named Confined Superelastic Dissipater (CSD). The proposed dissipater consists of a fused superelastic SMA bar as the functional kernel component encased in grout filled steel tube. The bar carries axial loads and dissipates energy through axial deformation, while the steel tube and infill grout restrain the bar and preclude buckling in compression. Quasi-static cyclic tests were conducted to characterize the hysteretic behavior and failure modes of CSDs. Next, a novel SMA-based hybrid damper that leverages the high tensile resistance and excellent self-cantering capability of SMA cables and non-sacrificial energy dissipation of a frictional damping mechanism was developed. The proposed damper, named Superelastic Friction Damper (SFD), employs judicious design features, manifested by additional advantages such as scalability for real-world application, reusability, ease of fabrication, and adaptability of its hysteretic response. A large-scale prototype damper was fabricated, and its mechanical behavior under repeated cyclic loading at different loading rates and ambient temperatures was characterized. Finally, the efficacy of the SFD in controlling the seismic responses of special steel moment-resisting frame was evaluated through nonlinear response history analyses. Engineering demand parameters of the frame with and without the damper were compared. Overall, the experimental and numerical results demonstrate that the SMA-based control devices can be implemented to meet higher performance objectives and achieve functional recovery of structures after a major earthquake, paving the way for designing resilient built environment.
