(CS2.5) Historic, Resilient, and Sustainable: Base Isolation Seismic Retrofit Considerations for a LEED Gold Rehabilitation of the Oregon Supreme Court Building

In anticipation of an impending Cascadia Subduction Zone earthquake in the Pacific Northwest of the United States, there is a push to seismically rehabilitate unreinforced masonry buildings – particularly, threatened historic structures. This presentation uses the Oregon State Supreme Court Building as a case study for integrating base isolation and building performance improvements to meet seismic, safety, and sustainable design goals in a historic building rehabilitation. Attendees will explore the decision-making process in determining a seismic retrofit method appropriate for an historic building and how base isolation can help meet desired building performance levels and LEED certification.
Beginning with predesign, this session stresses the importance of conducting a feasibility study to compare all applicable retrofit methods - including their costs and impact on historic fabric. When considering base isolation, it’s important to note that this retrofit method is not a one-size-fits-all solution to hide interventions below grade. A combination of a triple-friction-pendulum base isolation system, traditional shear walls, and furred partitions were required at the Supreme Court Building to meet performance objectives. The resulting impact to the historic fabric on upper floor levels was a lesson in managing client expectations and reviving skilled trades for feature restoration.
Additional tips will be shared for base isolation projects, including the benefits of applying the GSA “Preservation Zoning” standard to interior spaces to maximize retention of historic fabric and guide where structural interventions happen. The importance of involving a Construction Manager/General Contractor (CM/GC) from the beginning to advise on constructability, conduct selective destructive investigations, and perform in-situ structural and material testing will also be stressed. Lessons learned during construction means and methods will be shared, including challenges in salvaging and reinstalling existing finishes while integrating modern systems for an efficient, resilient, and historic building.
Completed in 2023, this project is the first base isolation retrofit of a historic building in Oregon to achieve LEED Certification, and among only two in the United States. It serves as an example of the ultimate sustainable preservation project using innovative technology – preserving history while ensuring longevity via seismic resiliency.