Structural Control with Seismic Base Isolation Technology

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Canadian cities are at significant risk due to seismic hazards. In addition to the potential for catastrophic damage to structures and loss of life, earthquakes present serious long-term challenges in the form of rebuilding and accommodating displaced people. Conventional approaches to designing structures for seismic loads focus on life safety, anticipating and accepting that damage to the structure will occur. State-of-the-art seismic protection technologies, such as base isolation, aim to reduce the seismic demand on the structure. The concept requires the installation of specialized devices that can accommodate large deflections without damage. The deformation due to the earthquake is concentrated at this flexible layer rather than being transmitted to the structure, which effectively protects the occupants from harm and the structure and the contents from damage. Provisions for base isolation technology have recently been included in the National Building Code of Canada. The design of base isolation devices has progressed towards complex adaptive devices. These devices allow the response of the structure to be tailored to the magnitude of the earthquake. Although the potential benefits of adaptive devices are promising, the performance of such devices at extreme load levels is not well understood. This may lead to unforeseen consequences or missed opportunities for improved performance. Furthermore, the design of a base isolation system must fully encompass and consider all load sources. For example, due to the inherent flexibility in base isolation devices, under low-level winds, the structure may be susceptible to small movement that interferes with the performance of vibration-sensitive equipment such as Magnetic Resonance Imaging (MRI) machines. Additionally, the optimal approach to control the maximum motion of the structure during extreme earthquake events has yet to be determined. There exists significant potential to utilize a base isolation system to not only improve the seismic performance of a structure, but to also have excellent vibration performance when subjected to other external vibration sources such as wind, rail and traffic. Failure to account for alternative vibration sources may reduce the utility of the structure and directly impact day-to-day activities. Failure to adequately design the structure for extreme earthquake events could be catastrophic and a life safety concern. The recent inclusion of base isolation in the National Building Code of Canada makes research in in this area relevant and timely for Canada and Canadian industry. The objective of this research is to mitigate seismic risk by promoting base isolation technology in Canada and throughout the world. It is also to guide designers to ensure that a base isolation system does not inadvertently negatively impact the vibration performance of a structure but enhances it.