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| Los Angeles City Hall Seismic Rehabilitation Project - Background |
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| The City Hall structure is generally described as comprising three major components: the "base" (basement to 4th floor), "midrise" (5th floor to 11th floor), and "tower" (12th floor to pyramid top at 32nd floor). The structure base measures 476 feet on the north south longitudinal axis, by 250 feet on the east-west transverse axis. The tower is 100 ft. square through the twenty-fifth floor and extends to a height of 452 ft. above Main Street. The Building's skeleton contains 8,167 tons of structural steel assembled with 900,000 rivets. The volume is approximately 12 million cubic ft., containing almost 20 acres of floor space. Exactly 430 structural columns support the approximately 200 million pounds of dead weight. Strengthening the building will add 30,000 cubic yards of concrete, 3,000 tons of structural steel, 5,000 tons of reinforcing steel, and an additional 68,467 million pounds of dead weight to the building. |
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During the past 70 years, regional earthquakes have caused significant damage to Los Angeles City Hall. Terra cotta cladding has been cracked, broken or destroyed at portions of the building's exterior where the frame succumbed to earthquake ground motion. With every significant earthquake, unanchored masonry debris breaks loose and is scattered about the building's interior including the exit stairwell, obstructing passage.
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| Modern advancements in earthquake engineering and high-rise building technologies have resulted in significant design and construction improvements for life and safety. Local, state and federal codes have been significantly revised in the intervening years since City Hall was first opened on April 26, 1928, and new laws have been added that mandate accessibility to a wide range of handicapped users. |
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| In June of 1990, a General Obligation Bond Issue was passed by the City's voters for the purpose of upgrading substandard public buildings including City Hall. In March, 1993 the City of Los Angeles, Board of Public Works, Bureau of Engineering engaged the services of Albert C. Martin & Associates and its consultants to undertake a comprehensive seismic, life safety and disabled access upgrade of the 29 story landmark. In January of 1994, the Northridge Earthquake damaged City Hall, requiring the emergency relocation of 1,135 people from the 5th through 27th floors, and eventually the relocation of the remaining 1,250 people. |
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| Because City Hall's many large ceramic mosaics and decorative ceilings, marble columns and wood finishes are particularly sensitive to earthquakes, a combination of technologies were chosen to protect City Hall from the shaking and twisting motions resulting from a seismic event. First, a technology called "base isolation" was chosen to dampen the energies let loose by an earthquake. Second, strengthening the building through the installation of additional structural steel and of shear walls will make the building more rigid and less likely to cause damage within the building during a seismic event. This combination of technologies maximizes the building's opportunity to withstand future seismic events. |
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| This project installs 526 isolators and sliders, 64 viscous dampers which are like huge shock absorbers, 30,000 cubic yards of concrete, 3,000 tons of structural steel, 5,000 tons of reinforcing steel, and 12,500 linear feet of shear walls. |
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