Pacific Northwest design and construction firms are well acquainted with seismic requirements related to structures. But, as we described earlier this summer, the upcoming 2018 International Building Code has implications that are unprecedented when compared to previous code updates.
Our coverage of the upcoming changes, specifically the seismic code updates, has spurred many conversations with our clients and partners. These conversations and common questions inspired us to design and deliver a series of seismic presentations, and the popularity of the presentations drove us to build a follow-up piece. Here, we apply the seismic code to three project types that are common to the region: a residential podium structure, a mid-rise tower and a high-rise tower.
Back Up… What’s Driving These Changes?
The seismic code updates are triggered by recent geotechnical discoveries associated with the Seattle Basin. The bowl-shaped geological depression, which is softer than bedrock and stretches from Everett to Tacoma, focuses and amplifies seismic waves. This basin effect means that earthquakes are magnified and shaking lasts longer. Geotechnical studies of the disastrous Jiji and Tohoku earthquakes, also located in deep basins, helped inform the new code. The data set gathered (from some of the most extensive networks of sensors and monitoring stations in the world at that time) gave scientists and geotechnical engineers new indicators related to the path and depth of ground motions across the basin. Evaluation of this information, when combined with data from more sophisticated equipment and other seismic events, contributes to the improved life safety codes.
Minimizing Impacts of the New Seismic Code
Collaborating with the region’s designers and contractors, we’re exploring techniques and layout options that will maximize performance without sacrificing an owner’s intended goals, budget, or delivery to market. While we acknowledge each site and program is unique, these examples reveal how we’re minimizing impacts for these project types.