Mason T. Walters is a Senior Principal at San Francisco Based Forell/Elsesser Engineers. He played a key role in the Salt Lake City & County Building’s original base isolation design. (m.walters@forell.com)
On March 18, 2020, the historic Salt Lake City & County Building experienced shaking from an M5.7 event with an epicenter nearly 9 miles away. Damage experienced by this base-isolated, unreinforced masonry structure was hardly perceptible compared to other aging structures of the region and barely newsworthy…a considerable credit to the vision of the original stakeholders and the designers of its retrofit, which took place in the mid-1980s.
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Imagine yourself inside a house that rests on a frozen, frictionless lake when a violent earthquake occurs. Apart from noticing some up-and-down vibration, how would you know the ground is shaking? The lack of a horizontal “connection” to the earth would allow the ice to shift horizontally without affecting the house. …