The Federal Emergency Management Agency estimates that the long-term value of earthquake losses to the general building stock in the U.S. is $5.3 billion per year. This value, known as the Annualized Earthquake Loss, is conservative because it does not include damages to lifeline infrastructure or indirect, long-term economic losses.
Credit: Bryan Christie Design
On Jan. 17, 1994, residents of the Los Angeles neighborhood of Northridge were jolted awake by the intense vibrations of a 6.7-magnitude earthquake. Scores of buildings and highways collapsed in the area, and after just 10 seconds, the trembler caused at least 57 deaths and up to $26 billion in damage—making it one of the costliest natural disasters in the history of the United States.
Since Northridge, which was the last major earthquake—in terms of damage, costs, and lives lost—to strike our country, significant advances have been made in seismic design and construction, from building materials and methods to research and technology. But as scientists grow increasingly wary of the next big one, the question arises about whether those advances are enough not only to protect lives during an earthquake, but also to keep buildings operational in the immediate aftermath.
All 50 states experience some level of seismic activity, but the western U.S. shoulders much of the brunt. A 2007 study led by the Southern California Earthquake Center found that San Francisco alone has a 63 percent chance of experiencing an earthquake of 6.7 magnitude or greater within the next 30 years. If a 7.2-magnitude earthquake hits the city, roughly 17 percent of its buildings will be unsafe to occupy and at least 2 percent will be unsalvageable, according to a 2010 report from the Applied Technology Council, a Redwood City, Calif.–based nonprofit corporation that advocates for the application of engineering resources to mitigate natural hazards. “The next major earthquake that strikes San Francisco will change the city and its people,” the report states.
Part of the concern stems from the fact that modern building codes outline only minimum life-safety requirements to prevent building collapse and give people time to egress during a design-level earthquake—that is, one that represents the maximum amount of ground movement that a structure is intended to sustain.
Developed and adopted by localities, building codes prescribe the minimum standard for buildings and infrastructure. In reality, however, the codes often end up as the standard to which structures are designed. They generally do not address the continued operations of nonessential structures—buildings that aren’t hospitals and fire stations. Buildings that become inoperable can lead to unsafe conditions and displacement, as well as lost income and tax revenue.
At the forefront of an outreach effort is Ibrahim Almufti, a San Francisco–based associate and structural engineer in Arup’s Advanced Technology + Research group. Almufti helped develop the firm’s Resilience-Based Earthquake Design Initiative (REDi) Rating System, a tiered checklist for architects, engineers, and owners to design buildings beyond life safety. REDi outlines criteria for designing new buildings to meet silver, gold, and platinum levels of earthquake resiliency, in a manner similar to the U.S. Green Building Council’s LEED rating system for sustainable design.
The system, Almufti says, aims to prevent significant damage to structures, architectural components and façades, building contents, and mechanical, electrical, and plumbing systems. “My objective is … to provide quality of life after a big earthquake,” he says. “We shouldn’t have to spend years and decades recovering from a 500-year earthquake.”
Almufti cites Christchurch, New Zealand, as an example. The city is still rebuilding three years after a 6.3-magnitude seismic event destroyed the city center in 2011 and caused upwards of $40 billion in damage. And with comparable building codes to New Zealand’s, the U.S. might find itself in a similar situation someday, Almufti says. “For code-designed buildings, the average amount that you need to spend to repair the building is about 25 percent of the total building value. If you have that much damage, [you] would probably end up demolishing the building”—a fate that befell many Christchurch buildings.
But Christchurch may not be the definitive barometer. Sissy Nikolaou, a senior associate and director of the geo-seismic department at Mueser Rutledge Consulting Engineers, in New York, points out that Christchurch had experienced several large earthquakes in a short period prior to the 2011 event. The resulting repetitive soil liquefaction—or the loss of considerable strength of water-saturated soil due to an applied stress—contributed significantly to the damage, she says. “It’s not a typical case study of an earthquake.”
Nikolaou contends that whether buildings in the U.S. should be designed beyond the code is a discussion that designers must have with their clients. “That process involves educating the client, owner, or agency about their local hazard exposure and associated risk exposure, and understanding their specific needs and goals for seismic protection beyond code,” she says.
Credit: U.S. Geological Survey (2008)
These days, few building owners and developers are interested in exceeding code. Reasons include limited finances, time, and interest. However, Almufti says a building can be designed to be earthquake resilient for less than 5 percent of a project’s construction cost.
While a building designed to code will likely sustain significant structural damage during a design-level event, an earthquake-resilient building will, in theory, experience only cosmetic damage and remain operational. Achieving this resiliency, Almufti says, is a matter of integrating advanced seismic technologies, such as base isolation and viscous dampers, and detailing architectural components for movement. Other design necessities: a façade that remains air- and watertight; elevators that stay operational; and interior partitions capable of handling significant displacement.
Some of the most earthquake-resilient buildings in the country are base-isolated hospitals in California, Almufti says. But though building codes for hospitals and other essential buildings are more stringent than those for nonessential structures, the current code does not even require base isolation for hospitals.
The forthcoming San Francisco General Hospital and Trauma Center building, designed by local firm Fong & Chan Architects with Arup as its engineer, will be base isolated and its structural elements will behave elastically in a design-level earthquake. Those features, coupled with the strict code requirements for the design of architectural and M/E/P systems, give the hospital a good chance of enduring significantly less damage than other hospitals that were built simply to code, and infinitely less damage than other code-designed buildings, Almufti says.
Designed by Fong & Chan Architects with Arup as its engineer, the new nine-story, 500,000-square-foot San Francisco General Hospital and Trauma Center incorporates a base-isolated foundation to ensure that the building—the only trauma center in the city—will remain operational after a seismic event.
Credit: Perretti & Park
While San Francisco and other seismically aware cities are effectively designing buildings for peril, other communities, such as those near the New Madrid Seismic Zone in the Midwest, haven’t been as proactive, says Tim Smail, senior vice president of engineering and technical programs at the Federal Alliance for Safe Homes. “There are lots of places throughout the country where communities are downplaying their risk.” Consequently, he says, “they are not taking advantage of those opportunities to build stronger against earthquakes.”
Smail attributes the inaction to a perceived low return on investment. “For low-probability events that are high-risk in nature, people have a very hard time wrapping their heads around what those mean,” he says. Spending “money now to mitigate or prepare for those events is just not in the forefront of people’s minds.”
Seismic resilience involves more than the stability of a single building, however. Associated infrastructure is also a factor. Effie Bouras, co-curator of “Considering the Quake: Seismic Design on the Edge,” an exhibition that recently appeared at the Center for Architecture in New York, notes that essential services such as water and electricity must also be maintained for buildings to be truly resilient and safe. “A non-collapsed structure that’s deprived of its essential services is no longer safe for its occupants,” Bouras says. “In effect, it’s absolutely useless when it’s needed most. This is something that still needs to be functionally addressed [in most communities].”
Utility continuity is also critical for fighting post-disaster fires, says Stephen Szoke, senior director of codes and standards at the Portland Cement Association. “Such fires can cause as much or more damage as the initial events,” Szoke says, particularly because water supplies are often limited. “There have been lots of papers written on the topic, but it’s not really been something that has been integrated into the design codes and the design standards.”
About 800 infernos blazed in Northridge and its surrounding areas following the 1994 earthquake, including at least one from a burst gas main that spread to nearby homes. Fire also spread rapidly in the San Francisco Bay Area after the Loma Prieta earthquake in 1989.
Szoke says the most important thing designers can do is help people “consider what they’re adopting as their building codes.” He urges architects and engineers to spread the message about seismic risks to government officials and the public.
Designers can also talk to project owners about the value of resilient design. Lance Jay Brown, FAIA, president of the AIA New York Chapter (AIANY) and founding co-chair of AIANY’s Design for Risk and Reconstruction Committee, says that owners need to know that spending extra money up-front for advanced seismic design will save them money over time. Like many long-term capital investments, the challenge lies in convincing people to plan for an event that could be decades or centuries away. When it comes to desired return on investment, “we live on a very short schedule,” says Brown, who’s also an architecture professor at the City College of the City University of New York.
While it is impossible to know exactly when the next major earthquake will come, designing buildings that can stand and function in the aftermath will help protect lives, limit damages, and expedite recovery. Going from building collapse to life-safety codes in the past half-century has been a huge achievement for the earthquake engineering community, Almufti says. “But we should be doing way better than that.”