Tall Order

by Nabih Youssef, (F.ASCE), Principal; Nabih Youssef & Assocs., Los Angeles,

Serial Information: Civil Engineering—ASCE, 1999, Vol. 69, Issue 10, Pg. 58-61

Document Type: Feature article

Abstract: Successive earthquakes have damaged the 32-story, 460 ft (140 m) tall Los Angeles City Hall, built in 1926. Masonry infill and concrete walls have cracked, and the terra cotta cladding has cracked, broken, or been destroyed on parts of the building's exterior. In 1997, the city began a four-year project intended to seismically strengthen the historic landmark and keep it safe and operational for years to come. Three schemes were considered: a reinforced concrete shear wall system, a reinforced concrete shear wall with steel superbrace system, and a base-isolation system with supplemental dampers. The base-isolation system turned out to be the most effective reinforcement plan, based on performance and cost. When the project is completed in July 2001, 416 rubber bearings and 90 sliding bearings will make the Los Angeles City Hall the tallest base-isolated building in the world.

Subject Headings: Base isolation | Earthquake resistant structures | High-rise buildings | Historic sites | Rehabilitation |

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