Seismic Isolation of Low-Rise Residential Structures

Despite the advances in structural engineering made in the last century, earthquakes continue to pose a major risk to the lives and livelihoods of many communities in Canada. Generally, single-family wood frame residential structures are fairly resilient to seismic effects, however, the aftermath of several earthquakes has demonstrated that while life safety was acceptable, the high economic losses were not. To protect against this danger to life and livelihood, the National Building Code of Canada (NBCC) provides several methodologies to design structures for seismic events. One of the most promising is an emergent technology known as base isolation. Base isolators are specially designed structural components that effectively act as a suspension system, isolating the structure from the ground motion effects. While this technology has proven effective at protecting structures and their occupants, the current methodology requires costly custom designs and comprehensive engineering. Thus, the application of this technology is likely to be expensive for common single-family residential structures. To eliminate this cost barrier to widespread application in low-rise residential structures, software was developed to perform the engineering seismic isolation design for structures designed according to Part 9 (Housing and Small Structures) of the NBCC. Currently, the NBCC does not provide a methodology to design base isolated structures, and so the program adapts the American Society of Civil Engineers equivalent lateral force procedure to NBCC requirements. The design and analysis of the base isolated structure is performed using pre-certified isolators whose properties have been previously verified, the structural characteristics and geometry, and site data. This allows the designer to augment a low-rise residential structure with a seismic isolation system without engineering involvement, providing an economical path for seismic isolation to become the rule in low-rise residential structures.