The Smithsonian Castle Renovation Seismic Isolation: Virtual Lecture

The Smithsonian Institution Building (SIB), also known as “The Castle”, is the original home of the Smithsonian and the Institution’s signature building, located prominently on the National Mall in Washington, DC. The building originally opened in 1855, and has subsequently seen many modifications, reconstructions, and repairs over the years. Many of the recent repairs have been in response to the Mineral Earthquake in 2011, the epicenter of which was located approximately 90 miles from DC. During the earthquake, the unreinforced masonry of the Castle suffered damage including the collapse of chimneys, displacement of finials, and cracking in the towers.

The Castle is now undergoing its first significant renovation and restoration in over 50 years with the Revitalize Historic Core project. Given the high cultural significance of the building as an artifact itself of the Smithsonian and the extent of damage incurred in the 2011 earthquake, the building will be structural retrofit for upgraded seismic design using base isolation. The isolators will decouple the building from the movement of the earth under a seismic event, and significantly reduce the movements and accelerations of the building and towers relative to a fixed base building. The Smithsonian has elected for this enhanced seismic design approach to protect the Castle not just for an ordinary building’s service life, but in perpetuity against a seismic event of a nearly 2500-year return period. Base Isolation has been used on a number of west coast historic and landmark buildings in the United States, but the Castle will be a landmark example of a seismic retrofit using base isolation on the east coast.

Though DC is a traditionally low seismic zone, the geometry of the Castle, with slender projecting towers and chimneys built of unreinforced masonry, make this building particularly sensitive to amplified accelerations from ground movements. Prior design studies for the project investigated using traditional retrofit measures, such as concrete shear walls or steel brace frames installed inboard of the existing masonry walls. These options were both more destructive to historic fabric, especially at the towers, and could not achieve the same enhanced seismic performance feasible with base isolation. By incorporating the technology of base isolation, and by using modern nonlinear dynamic analysis procedures for nuanced evaluation, the building can be seismically retrofit to meet the Smithsonian’s intended enhanced performance objectives in a way that allows for a more sensitive approach to historic preservation.

LEARNING OBJECTIVES

After attending this webinar, participants will be able to:

• Understand the technical challenges associated with incorporating base isolation into an existing historic building in a lower seismic zone.
• Explain how base isolation improves seismic performance and can be used as a preservation tool.
• Compare pros/cons of traditional retrofit options versus base isolation.
• Understand the history and structural makeup of the Smithsonian Castle.

Please note: Video will be recorded.

Margaret Cowie is a licensed structural engineer working in Washington, DC. Margaret, now a Senior Project Engineer, joined Silman in 2015 after graduating from Columbia University with a BS and MS in Structural Engineering. She is a member of the Association for Preservation Technology DC Chapter and the Association for Preservation Technology International. She has worked both in the Silman’s New York and DC offices, and her project work encompasses a range of building types and systems, with a focus on historic preservation and adaptive reuse. Much of Margaret’s work has focused on analysis of unreinforced masonry structures, including restoration of the thin-shell Guastavino tile at the waiting room ceiling of Michigan Central Station and seismic upgrades using base isolation at the masonry towers of the Smithsonian Castle.