The State of California has had earthquake provisions in its building codes dating back to the 1925 Santa Barbara earthquake, and significant improvements were made after the 1933 Long Beach earthquake. Since then, there have been constant improvements to the Building Codes, eventually resulting in the Uniform Building Code, especially beginning in 1960 when the Structural Engineers Association of California (SEAOC) published its Blue Book periodically.
At 6 a.m. on Feb. 9, 1971, a magnitude 6.6 earthquake struck outside Los Angeles in the foothills above the San Fernando Valley. The San Fernando earthquake (also known as the Sylmar earthquake) had a Modified Mercalli Intensity (MMI) of XI (Extreme), which caused extensive damage and included significant surface faulting. An estimated half a billion dollars in damages and 65 deaths were attributable to the earthquake. Most of the deaths occurred in two nearby hospital complexes, Olive View and Veterans, both of which suffered significant damage.
The Olive View Hospital included a new five-story Medical Treatment and Care Building, a new reinforced concrete building completed in December 1970 and built to the then-current earthquake-resistant codes and suffered extensive damage. The difference in stiffness between the weaker first floor and the stiffer upper floors concentrated the earthquake loads on the first floor, nearly causing its collapse. As a result, three of the four concrete stair towers fell away from the building. The near collapse of this brand-new critical building called into focus the need for better ductile performance in reinforced concrete structures.
As a result of the damage caused by this earthquake, several improvements were made that directly or indirectly improved the building code:
- Due to the significant damage to the new reinforced concrete hospital buildings at Olive View Hospital from this earthquake and later earthquakes, extensive changes were made to the building code to improve the ductility of reinforced concrete structures. This was done by increasing the amount of reinforcing steel to improve concrete confinement in reinforced concrete and improving reinforcing requirements in roof and floor slab systems. This marked a significant change in the building code, and all structures built before this change are referred to as non-ductile concrete buildings and, in some larger jurisdictions and situations, are now required to be evaluated for safety.
- Due to the extensive damage caused by the earthquake, the National Science Foundation (NSF) and what was then the National Bureau of Standards (now the National Institute for Standards and Technology, or NIST) funded a new organization, the Applied Technology Council (ATC), to develop a single document that incorporated a series of new concepts and procedures for seismic design for future code adoption. The Tentative Provisions was published in June 1978 as ATC 3-06. This publication went on to serve as the basis for the FEMA NEHRP Recommended Seismic Provisions for New Buildings and Other Structures, which ultimately became the basis for the seismic provisions of the International Building Code and ASCE 7 Minimum Design Loads and Associated Criteria for Buildings and Other Structures.
- Prior to the San Fernando earthquake, there was disagreement over what maximum ground motion values should be used for design purposes. As a result of this earthquake, the California Strong Motion Instrumentation Program (CSMIP), a program under the California Geological Survey, was initiated in 1971. This program resulted in the instrumentation of numerous buildings, structures, and free field sites. These instruments provided a wealth of information and strong motion records, especially in subsequent earthquakes, resulting in significant improvements to the building code.
- Because of damage due to surface fault ruptures during the earthquake, the Alquist-Priola Special Studies Zone Act was passed by the California legislature in 1972 to reduce future damages due to surface faulting or fault creep. This Act restricts the construction of buildings over potentially active faults, as identified by the state geologist.
- California passed the Hospital Safety Act of 1972, which, in part, required consideration of geological and seismological issues to ensure that all new and retrofitted hospitals are sited, designed, and constructed to remain operational after an earthquake.
- The extensive damage and repair cost got the attention of the U.S. Congress, which had for years considered the need for a coordinated federal program to address the earthquake hazard. In 1977, this resulted in the Earthquake Hazards Reduction Act, which created the National Earthquake Reduction Program (NEHRP).
Olive View Hospital was rebuilt using the new building code with updated requirements for reinforced concrete construction. It was constructed above those minimum code requirements, resulting in a much more robust structure. That building was tested in the 1994 M6.7 Northridge earthquake. It suffered very little damage and remained operational.