California seismic building codes apply to all existing buildings with at least one masonry bearing wall that is not reinforced. There are some exceptions for buildings in particular occupancy categories. There are also earthquake resistant requirements in the California Building Code for new buildings. The codes, revised after devastating damages following several major earthquakes, are some of the strictest in the United States. They are credited with preventing serious damage from successive earthquakes.
After a severe earthquake in California in 1971, significant enhancements to the building codes pertaining to earthquakes were made. The first real test of the improvements came in an earthquake that hit Los Angeles on January 17, 1994. Structures built or strengthened under the new codes experienced limited damage, while older buildings and other construction such as those bridges that had not been retrofitted suffered more damage. The revised codes prevented many buildings from collapsing but could not prevent collateral damage to HVAC and lighting systems in many cases.
The revised code requires specific features and tests for masonry used in construction. For example, brick walls must meet specifications for facing, bonding and maximum distances between headers. Masonry quality must be tested using in-place shear tests by actually displacing a single brick and testing for movement when a load is applied. There are four different quality specifications for mortar and three for masonry used in construction. Wall anchors have to be tested and pass requirements in the code. Embedded wall bolts are to be periodically inspected.
Although new and retrofitted buildings in California have performed much better in earthquakes, neither the revised code nor other building codes adequately addresses all of the associated elements of construction. In the 1994 earthquake there were more than 1,300 breaks and leaks in natural gas pipe lines in the area. A number of fires were caused by these leaks. Millions lost power from damage to electrical substations and towers. The code did not deal with modern parking structures, which led to some collapses.
Continuing application of the revised earthquake code after the 1994 event meant that when a 5.4 quake struck Los Angeles July 29, 2008, there was limited damage, such as a few water main breaks, but no reports of serious injury. There are still older buildings that have not been retrofitted and these did have some shear cracks. By having perhaps the strictest earthquake code in the country, not only was destruction limited and lives saved, the insurance industry was saved from incurring significant costs.
The actual provisions of California's earthquake code requirements of course only apply to jurisdictions in California. However, other states and municipalities have strengthened their codes, but there is still a wide variation across the country. The national Uniform Building Code was revised to take into account California's experience. Generally states adopt this code, but often enforcement is left up to local authorities where it can vary widely. Also, retrofitting existing buildings, particularly in geographically vulnerable areas, can be an extremely costly project.
- Photo Credit Charles R Anderson
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