The strong earthquake that struck the Los Angeles area last January 17 provided the first full-scale test of modern seismic structural codes and revealed both successes and deficiencies in current construction practices and codes, according to a report released today by the Commerce Department's National Institute of Standards and Technology.
Eight NIST building and fire researchers were part of a federal agency reconnaissance team that also included experts from the Federal Emergency Management Agency, Federal Highway Administration, Department of Housing and Urban Development, and U.S. Geological Survey.
"This report will serve as a valuable guide for those responsible for ongoing reconstruction efforts and will help Los Angeles and other communities reduce damage from future severe earthquakes," said Secretary of Commerce Ronald H. Brown, the Clinton Administration's representative on California's economic recovery.
In the United States, most seismic building codes are adopted and enforced at the state and local level. Following a devastating earthquake in California's San Fernando Valley in 1971, many improvements were made to earthquake codes in California and other states.
This report says most structures designed and built after these code changes were made performed well. The bulk of the damage occurred in older structures known to be vulnerable to earthquake shaking, such as un-reinforced masonry buildings. However, there were some unexpected failures, such as the collapses of relatively modern parking garages. Code provisions for parking garages need to be updated, the report concludes.
Most bridges designed using standards developed after the mid-1970s and most older bridges that had been retrofitted came through the strong ground-shaking in good shape. "While this implies that the current seismic design standards for bridges are adequate, we should not be lulled into a false sense of security," states the NIST report. "Despite the good performance of many bridges in this earthquake, we cannot yet predict the level of damage to bridges which would be caused by an earthquake with a larger magnitude (around 8.0) or which would be more centrally located in the Los Angeles area."
Inadequate reinforcement in columns was the major cause of severe damage in six major bridges. Other problems causing bridge failure or damage included shorter columns in bridges with columns of varying heights; skewed or irregularly shaped bridge spans; and unstable, steel rocker bridge bearings.
While the earthquake demonstrated the success of modern building codes, it also demonstrated their limitations, said NIST. Most of today's earthquake codes are intended primarily to prevent a structure from collapsing. They are not intended to prevent damage to property or systems such as lighting, air conditioning and heating. As a result, several hospitals were forced to evacuate patients, and the entire Los Angeles County school system was shut down.
While it is possible to design and construct buildings that can continue functioning after a major earthquake, said NIST, this greater protection adds cost. Engineers alone cannot answer the question of how much protection should be provided. All affected parts of society should be involved in weighing the costs against the benefits to determine how much protection the codes should provide.
The NIST team also found that damage to lifelines, including water, gas, telecommunications and transportation systems, caused serious disruptions and in some cases contributed to post- earthquake fires. In contrast to buildings and highway bridges, no nationally applicable design and construction practices are available for new or existing lifelines.
In particular, over 1,300 breaks and leaks in the area's natural gas pipes were reported. Most of the damage occurred in older steel pipes; plastic ones performed well. A significant number of the 30 to 50 fires occurring after the earthquake were caused by broken or leaking gas pipes.
Many fires continued to ignite days after the earthquake when power was restored to damaged buildings. NIST recommends that criteria be developed to help utility personnel assess when it is safe to restore electricity.
Damage to electrical equipment, such as transmission towers, high voltage substations and ceramic circuit breakers, caused nearly 2 million people to lose electrical power immediately following the earthquake. But, 95 percent of the power was restored within two days. Lessons learned from previous earthquakes helped improve the performance of electric power systems through stricter equipment qualification requirements and better installation practices, said NIST.
In addition to recommending ways to improve shortcomings in construction codes and practices, NIST also said more education is needed to help building designers, constructors and regulators recognize and produce more earthquake-resistant structures. "It is possible for every element of a building to meet code requirements, yet for the building as a whole to perform poorly in an earthquake," said the NIST report. "Education is needed to transfer the knowledge on building performance gained from this and other earthquakes to the people who can apply these lessons on a daily basis."
As part of the National Earthquake Hazards Reduction Program, NIST conducts research and provides technical support to the private sector and government agencies that are working to improve the performance of structures subjected to earthquakes. Since 1971, NIST has participated in 10 earthquake investigations.
A non-regulatory agency of the Commerce Department's Technology Administration, NIST promotes economic growth by working with industry to develop and apply technology, measurements and standards.