Cost-Effective Seismic Isolation Systems for Structural Retrofit Applications

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As the existing building stock ages and the structural engineering community furthers its knowledge on seismic behaviour and design, an increasing number of buildings are found to be seismically vulnerable. In New Zealand, which has design codes and construction methods resembling those in Canada, the Christchurch earthquake resulted in 185 deaths and over $40 billion in economic losses. One option to protect buildings and their occupants is seismic isolation which introduces a flexible layer, usually at the base of the building, limiting both forces transmitted to and deformation within the building. This improves the performance of both the structure and the nonstructural components, including architectural elements, mechanical and electrical systems, and building furnishings. However, due to the initial construction premium, seismic isolation is currently viewed as a luxury retrofit method, and its use has been limited. **Traditional isolation approaches call for a seismic gap around the building and stiff layers both above and below the isolation plane. Furthermore, in the case of retrofits, if the existing building is deemed too flexible, it must first be stiffened before it is isolated. These aspects add significantly to the initial costs of implementing isolation. By understanding the interaction between the isolation system and the surrounding structural elements, the cost of isolating both new and existing structures may be minimized by reducing structural design requirements. Besides reducing initial costs, this would also increase the variety of structures for which isolation retrofit may be feasible, making it applicable to soft-story buildings, under-designed low-rise and mid-rise buildings, or buildings in which additional stories are desired but the original structure cannot accommodate the increased lateral seismic loads. **By limiting structural damage and, often more importantly, reducing damage to nonstructural components, traditional seismic isolation has been shown to reduce lifecycle costs for new construction. Improved structural and nonstructural behaviour can further translate into minimized environmental impacts over the lifecycle of the building by limiting needs for repair or demolition after earthquakes. However, further investigation is needed for retrofit applications and buildings with reduced cost isolation configurations. With the overarching goal of advancing the safety and sustainability of earthquake prone communities, the proposed research will promote the adoption of isolation for retrofit projects through decreasing initial costs while also exploring potential lifecycle benefits. While the focus of the proposed research will be on building retrofit projects, the research will have direct applicability to new buildings. The findings of the research will contribute significantly to seismic isolation provisions in future versions of the National Building Code of Canada (NBCC) which is currently within the plans of the Standing Committee on Earthquake Design.