Destructive seismic events continue to demonstrate the importance of mitigating these hazards to building structures. Structural control has been considered one of the most effective strategies to protect buildings from extreme dynamic events such as earthquakes and strong winds, and has been applied to numerous real buildings in recent years.
Structural control strategies can be divided into four categories: passive, active, semi-active, and hybrid control. Because passive control systems are well understood and require no external power source, they have been accepted widely by the engineering community. However, these passive systems have the limitation of not being able to adapt to structural changes and to varying usage patterns and loading conditions. While active systems are able to adapt various conditions, they require a significant amount of power to generate the necessary large control forces; guaranteeing the availability of such power during seismic events is challenging. Moreover, the stability of active systems is not ensured.
To compensate for the drawbacks of passive and active systems, semi active control systems have been proposed. Semi-active control devices possess the adaptability to flexible external inputs, do not require large power sources, and do not have the potential to destabilize the structural system. However, semi-active control has been slow to be accepted by engineering practitioners.
The focus of this dissertation is the improvement and the validation of semi-active control strategies, especially with magnetorheological (MR) dampers, for building protection from severe earthquakes. To make semi-active control strategies more practical, further studies on both the numerical and experimental aspects of the problem are conducted.
In the numerical studies, new algorithms for semi-active control are proposed. First, the nature of control forces produced by active control systems is investigated. The relationship between force-displacement hysteresis loops produced by the linear quadratic regulator (LQR) and the linear quadratic Gaussian (LQG) algorithms is explored. Then, new simple algorithms are proposed, which can produce versatile hysteresis loops. Moreover, the proposed algorithms do not require a model of the target structure to be implemented, which is a significant advantage. The seismic performance of the proposed algorithms on a scaled three-story building model is compared with the LQG-based clipped-optimal semi active control and LQG active control cases.
In the experimental studies, the effectiveness of semi-active control strategies are shown through real-time hybrid simulation (RTHS) in which a MR damper is tested physically. In this dissertation, two new structural control methods proposed in the literature recently are investigated, i.e., smart outrigger damping systems for high-rise buildings and smart base isolation systems consisting of passive base isolations and semi-active control devices. The accuracy of the RTHS employing the model-based compensator for MDOF structures with a semi-active device is discussed as well.
The research presented in this dissertation contributes the improvement and prevalence of semi-active control strategies in building structures to mitigate seismic damage
