By John McDonald, S.E., Stefanie Chamorro, P.E., and Geoff Bomba, S.E.
Driven by the importance of the Oregon State Capitol and disproportionate seismic damage from the 1993 Scotts Mills seismic event, the Oregon Legislature moved forward with measures to protect and preserve the historic building. The project includes a seismically base-isolated retrofit of the 1938 Capitol building, which is a non-ductile brick infilled concrete frame structure with marble cladding. The Capitol is flanked by a pair of five-story 1977 reinforced concrete buildings retrofitted using a fiber-reinforced polymer (FRP) strengthening system, which remain fixed base structures. The seismic isolation system of the Capitol utilizes a triple friction pendulum system tuned to reduce the acceleration of the building during a Cascadia Subduction Zone (CSZ) seismic event. Once complete, a new occupied level will be constructed below the existing building footprint to increase program space and meet the changing needs of the Oregon State Capitol.
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