Earthquake Mitigation Technology: Life, Safety, Structures, Contents, and Function
- Published on Sunday, 28 October 2007 23:48
Such limited protection is not consistent with the needs of commerce or emergency facilities, which must remain operational after an earthquake, nor does it protect the contents of a building. Two earthquakes which struck near the Lawrence Livermore National Laboratory in California, within two days of each other in January of 1980, caused a total of $10 million in damage. Nearly half of the damage was to laboratory equipment, testing systems, and other building contents.
Public policy should require design professionals to construct buildings with specifications exceeding minimum code requirements and which will protect building contents and function during and after severe earthquakes. A step in this direction was taken in 1972 when the California Legislature passed the Hospital Seismic Safety Act, which requires hospitals to remain operational “as much as practicable” during and after an earthquake.
A newly-applied strategy in earthquake design called seismic, or base, isolation is intended to prevent earthquake damage to structures, buildings and building contents. One type of seismic isolation system employs load bearing pads, called isolators, made of laminations of high damping rubber vulcanized to thin steel plates. They are located strategically between the foundation and the building structure and are designed to lower the magnitude and frequency of seismic shock permitted to enter the building. They provide both spring and energy absorbing characteristics. The optimum use of seismic isolation is in buildings up to 15 stories tall, depending upon the building’s height and base ratio, and then only where soil conditions permit.
The first seismic isolation system was proposed by Dr. Johannes Calantarients, an English medical doctor, in 1909. His diagrams show a building separated from its foundation by a layer of talc which would isolate the main structure from seismic shock. He also designed utility water and gas connections which would flex during an earthquake.
Frank Lloyd Wright used the seismic isolation concept when he designed the Imperial Hotel in Tokyo, built in 1921. Wright had the structure built atop eight feet of hard soil above a layer of soft mud which Wright believed would be “...a good cushion to relieve the terrible shocks. Why not float the building above it.” Instead of sinking support piles into bedrock, Wright had the building supported by closely spaced short piles which penetrated only the upper soil stratum and allowed the building to float on the mud substratum. The Imperial Hotel was one of the few western style buildings to survive the devastating Tokyo earthquake of 1923. Economics and the effects of air pollution on the soft stone used in the hotel’s construction brought about its demolition in the 1960s.
The development of rubber and steel bearings capable of supporting buildings came about in the late 1960s after decades of experience with bridge bearings showed that rubber is a reliable engineering material. High precision elastomeric bearings with many thin laminations are now used in helicopters to replace bearings where motion is cyclic rather than rotary. A different form of bearing is used for fenders on docks and wharves, and in supports of offshore drilling platforms. In England, where the concept began, elastomeric bearings have been used since the 1960s to isolate buildings from the vibrations of subway trains running beneath them. The idea was extended to seismic protection in the early 1970s when the Malaysian Rubber Producers Research Association of the United Kingdom, and the National Science Foundation, carried out shake table experiments at the Earthquake Engineering Research Center at the University of California, Berkeley.
The first application of the technology in the United States was in the construction of the Foothill Communities Law and Justice Center in Rancho Cucamonga, California, built in 1985 near the San Andreas and San Jacinto earthquake faults. The building dimensions are 414’ X 110’. It is four stories tall and mounted on 98 isolator bearings, which are designed to allow the building to withstand a shock of 8.5 on the Richter scale.
Three earthquakes have occurred in the vicinity of the building, since construction was completed, and all triggered seismic measuring instruments. The largest and most recent occurred on February 28, 1990, near Upland, California. It had a Richter scale magnitude of 5.5, and the epicenter was about 7 miles from the Law and Justice Center.
According to the office of Strong Motion Studies report of March 2, 1990, ground acceleration at the base of the building foundation was 0.16g, and above the isolators, 0.08g, indicating the shock into the structure was halved in magnitude by the base isolation system. The acceleration of the building at roof level was 0.16g thus showing an amplification of the structure itself of 2.
Two other buildings in the vicinity of the earthquake were also instrumented. One was constructed with unreinforced masonry walls and the other was steel reinforced. The instruments in these structures indicated the ground shock, directly applied to the foundation, was amplified three times by the building structure resulting in an acceleration at roof level of 0.37g.
There is one clear message from the earthquakes of the past decade throughout the world—there is great uncertainty in the degree and extent of their impacts on industrial and business organizations. Firms that suffer heavy damage to their facilities see:
- Competitors seizing market share;
- Profitability eliminated;
- Security compromised;
- Unknown liability claims;
- and Bankruptcy.
Yet those firms and organizations suffering only minor damage, due to the use of earthquake resistant facilities, will find they can use the earthquake as a business opportunity.
THE INITIATION OF POLICY
In 1981, the California Engineering Foundation (CEF) introduced the California Seismic Safety Commission to the idea of seismic isolation. This was the beginning of the first use of mitigating technologies for seismic design in California and the U.S. CEF continued its efforts to add this technology to the state’s technology arsenal over the next eight years and in January, 1989, the CEF convened a major policy conference on earthquake hazard mitigation for engineers, architects, building owners, building officials, and public policy makers to:
- Highlight seismic isolation and other damage mitigating design strategies that protect buildings and their contents from the devastation caused by earthquakes;
- Review the status of new technologies and their applications;
- Identify impedances to their utilization;
- Evaluate the legal/liability factors associated with the new technologies; and
- Develop recommendations for policy and education changes and additional research.
Issues Related to Conference Objectives
Earthquakes are a reality in many areas throughout the world, and California is the most seismically active state in the contiguous United States. California state government devotes a significant effort to earthquake preparedness and emergency services, with a focus on protection of life and limb and how the state could “get well” after an earthquake. The strategies discussed in the CEF conference focused on preventing loss and damage before the earthquake with new building design technologies.
Issues associated with the application of new earthquake hazard mitigating technologies include:
- Life cycle analysis, design and construction costs.
- Risk and benefit considerations of new design approaches.
- Exposure and liability of using new design approaches.
- Insurance considerations.
- Research needs.
- Analytical design approaches and verification.
- Effect on state codes and code impedances.
- Limitations in the application of new strategies.
- Status of policy in the design professions.
- Legislative mandates on earthquake design standards.
- State licensing implications.
- Educational requirements.
- Technology awareness, design applications, and manufacturing technologies.
- Seismic isolator design and manufacturing process control.
- Seismic isolator testing and characterization.
- Analytical design and analysis programs and their standardization.
- Standardizing credible seismic events for design criteria.
- State funded research.
- Federal funded research.
At the conclusion of the conference, California State Senator Don Rogers (R-Bakersfield), assembled a task force with representatives from the CEF, the Structural Engineers Association, California Seismic Safety Commission, State Architect’ office, Office of General Services, the California Council of Civil Engineers and Land Surveyors, University of California, and individual consulting.
The task force evaluated the conference findings relating to state policy. Senator Rogers incorporated the findings into Senate Bill 920, which was signed into law by the Governor in September, 1989, three weeks before the Bay Area earthquake on October 17, 1989. The new law requires, among many things, the State of California demonstrate earthquake hazard mitigating technology in three state structures — two existing buildings and a new one. Senator Rogers introduced two additional bills during the 1990 session. One bill modifies the law created by SB 920, and the other is a Constitutional amendment to provide incentives for businesses to retrofit earthquake hazard mitigating technology into existing buildings.
NEW POLICY DIRECTION NEEDED AT THE FEDERAL LEVEL
The federal government has yet to incorporate earthquake hazard mitigating technology, as defined in the new California law, into new building construction or in retrofitting existing buildings in seismically active areas. Additional studies of the 1989 Bay Area earthquake have been funded, but none are associated with design and construction of new buildings, or the retrofitting of unsafe, older buildings. The federal government should assume a lead role in protecting federal buildings, contents, and function, so as to encourage business leaders to take similar action with private buildings. The state and federal governments, universities and the private sector should further collaborate to increase the availability of new laboratory equipment, such as large shake tables, for testing of base isolation components and systems. New, large shake tables have been developed by the U.S. Department of Energy’s, Energy Technology Engineering Center, managed by Rockwell International, in Canoga Park, California. There are opportunities for joint industry/federal laboratory research efforts under the Federal Technology Transfer Act of 1986, and the National Competitiveness Technology Transfer Act of 1989.
Industry and/or state government should begin to classify and categorize types of buildings that would benefit from seismic isolation and other earthquake hazard mitigation technologies. The Japanese have extensively reviewed California research and have over 60 projects underway using earthquake hazard mitigating technology, including base isolation. Meanwhile, there are 15 projects completed or under design or construction including new buildings or older retrofits, in the U.S. Thirteen of the projects are located in California while the remaining two are in Salt Lake City, Utah. One of the recently approved projects under design is a 850,000 square foot medical center located in San Bernadino County, California, and when completed will be the largest building to use base isolation.
President Carter convened a task force after Mount St. Helen’s erupted in May, 1980, to examine the seismic vulnerability of military and defense facilities. The task force completed its study and was disbanded by the subsequent administration with little action taken. Some of the nation’s most critical military installations are located in earthquake prone areas and should be given immediate attention by the Department of Defense.
A new concept of national defense should consider natural threats. Economic strength is as vital to national security as is military strength. A major earthquake will have an immediate and long range effect on the nation’s economy, since major destruction will occur to manufacturing centers and infrastructure. The U.S. Geological survey predicts a 50-60% probability of a major California earthquake in the next 30 years, and further postulates a $50 billion loss in property damage alone. No figures are available for long term losses. The Loma Prieta earthquake of October, 1989, was moderate by seismological standards. The 1906 San Francisco earthquake was over 40 times more powerful than the October 17 earthquake, and is a more realistic example of the devastation that could occur from a severe earthquake.
Earthquake design in California is dictated by state and local government interpretation of the uniform Building Code, which provides specifications for minimum protection to structures. Structures built to code specifications should not be damaged in a minor earthquake up to 4.5 on the Richter scale (M4.5), structurally damaged by a moderate event up to M6.5 Richter, nor collapse in a major earthquake above M6.5 Richter.
New seismic technology designed to protect buildings, building contents and building function in earthquakes in the M8-plus Richter range is available to design professionals and the construction industry. However, familiarizing engineers, architects and construction regulators with new seismic technologies will take time.
Government may also set an example. The state must facilitate the use of new earthquake hazard mitigating technologies by using them in state buildings and creating a positive environment for these new strategies in the private sector.
one incentive would be liability protection for professionals who incorporate new designs into projects. In a highly litigious society, architects and engineers are now caught between two legal mandates in building design. On the one hand, any deviation from codified practices using earthquake mitigation technologies could result in a lawsuit. On the other hand, a design professional can be sued for not using new technology superior to code requirements. Most design professionals prefer to adhere to the code.
Building owners must be convinced that insurance will not indemnify all losses due to earthquakes, and that the best insurance is prevention of damage through design.
After any natural disaster, there is usually a flurry of activity to examine public policy. The earthquake hazard mitigating policies in California have deviated from this general phenomenon in that the California Engineering Foundation efforts affected policy changes independent of a specific earthquake. In fact, as mentioned before, SB 920 was signed into law three weeks before the Loma Prieta quake. Other changes in policy include the incorporation of base isolation in the Uniform Building Code, and in California, this mitigating strategy has been included in the Structural Engineers Association “Blue Book.” The California Office of State-wide Planning and Development has included base isolation in its hospital regulations. However, the Loma Prieta quake did stimulate many of the retrofit projects in the San Francisco area. But the window of opportunity for change closes very quickly—even after cataclysmic events. The responsibility lies with the technical community to develop and implement strategic plans necessary to move public policy in accordance with the development of new technologies, and educate the public about the urgency of earthquake hazard mitigation.
Dr. Robert J. Kuntz is President of the California Engineering Foundation—a nonprofit organization addressing the socioeconomic and political aspects of science and technology.
Daniel L. Tanner is the California Engineering Foundation’s Economic Consultant.
This article adapted from Vol. 5 #4.