This study developed a temperature controlled semi-active tuned mass damper (TMD) using shape memory alloy (SMA) for civil structural applications. It addressed the off-tuning issues caused by the variances in structural mass and stiffness when in service, since off-tuning of the TMD increases the structural response. The effect of in-service temperature on SMA can provide adaptive dynamic properties to TMD. Therefore, the natural frequencies can be adjusted to an optimal range.In this thesis, the material characterisation of SMA is studied through acting dynamic cyclic loading. It was found that Cu-Al-Mn SMA has a superior self-centring capacity, adequate fatigue life and a large damping ratio. By controlling the in-service temperature of a cantilever SMA beam, it was found that the stiffness of the SMA increases and the damping ratio reduces with higher temperatures in free vibration. It is important to note that these properties are increasingly sensitive to temperature when pre-stress is applied and the pre-stressed level is approximate to the phase transformation temperature. The potential for employing SMA with temperature control in a semi-active TMD system is considerable.The feasibility of this type of semi-active TMD was studied experimentally by mounting the SMA-based TMD on a cantilever beam to reduce the excessive vibration caused by off-tuning. For lateral loadings, the non-pre-stressed SMA was applied to a steel framed structure for addressing the off-tuning issues experienced under actions caused by earthquakes and wind by conducting shaking table tests. Cooling the SMA can effectively retune the structural frequencies and attenuate the vibration, but heating the SMA contributed limited effectiveness. This is because the damping losses and stiffness variance are relatively small while heating. In simulation studies, a timber floor-TMD system was modelled under vertical excitations. Both heating and cooling of the SMA can effectively retune the structure from its off-tuned state and can consequently reduce the excessive vibration. Moreover, temperature control of the SMA can shift the natural frequencies to avoid resonance under harmonic loadings. Based on the theoretical and experimental studies in this thesis, the temperature controlled semi-active TMD with SMA can address the off-tuning issues experienced by civil structures under various in-service excitations.
|Date of Award
|27 Jun 2017
|Wen-Shao Chang (Supervisor) & Chris Williams (Supervisor)