Full Session with Abstracts
Less than 100 yards from the Hayward Fault and built entirely of unreinforced concrete, the 1903 Hearst Greek Theater posed serious life-safety dangers in a large seismic event. Because the theater is a California landmark, listed on the National Register of Historic Places, the sorely needed seismic improvements and renovation work it required could not alter its appearance.
The most effective approach was to strengthen and stiffen the critical areas dominating the structure’s movement and design the retrofit in harmony with its natural dynamic response. The stiffening was provided by new strongback columns that were hidden in the colonnade’s existing cavities and founded on large concrete footings anchored by 40-foot drilled piers. Reinforcement was installed in the existing void in each column, which was then filled with concrete. The old copper roofing was removed, the center protrusion chipped away and replaced with a reinforced concrete yoke that tied all the new reinforcement together. Glass-fiber reinforcing polymer was added to the back of the entire colonnade, strengthening the panels for in-plane shear and out-of-plane loads. The foundation was stabilized under each column with large concrete underpinning piers and jacked to transfer existing loads to the piers.
Lastly, to ensure proper execution of the work and reduce the risk of destabilizing the existing fragile structure, a detailed construction sequence was developed to guide the contractor's approach to demolition and reconstruction. Owing to all these measures, the seismic performance rating for the theater was revised to “Good” from "Very Poor."
Architect: Cody, Anderson, Wasney Architects
Owner/Developer: University of California at Berkeley
Structural Engineer: Tipping Structural Engineers
Construction Cost: $5.6 million