By Catherine A. Cardno, Ph.D.
The City of Los Angeles has passed an ordinance requiring the seismic retrofit of "soft-first-story" wooden buildings and nonductile concrete buildings to ensure life safety.
In the magnitude 6.7 Northridge, California, earthquake that occurred at 4:30am PST on January 17, 1994, more than 40,000 buildings were damaged in Los Angeles, Ventura, Orange, and San Bernardino counties—including nonductile concrete buildings, like this one, in which the third story collapsed onto the second. New regulations call for the strengthening of this type of structure as well as so called “soft-first-story” structures throughout the state in preparation for the next significant earthquake. USGS
November 3, 2015—When it comes to the civil and structural engineering of a building, life safety is exactly what it sounds like: the ability of a building to remain standing so that everyone within the building during a specified disaster can exit alive. The building might be irreparably damaged during the event, and occupants might be injured due to the contents of the building shifting, but the building will remain standing. It is to this standard that the City of Los Angeles now requires that its so-called "soft-first-story" wooden buildings and nonductile concrete buildings must perform. Soft-first-story structures are typically small-scale structures with large openings or a limited number of structural walls.
The new ordinancebecame the nation's strictest seismic retrofit mandate upon its unanimous passage by the 12-member Los Angeles City Council on October 9. Los Angeles Mayor Eric Garcetti signed the ordinance into law on the same day.
"Today, Los Angeles makes good on our promise to take action before it's too late," Garcetti said in a statement released by his office following the signing. "Together, we're leading the nation in requiring this level of building safety retrofit before, not after, the big quake we know is coming," he said. "We know that it's not just the lives lost, but the lasting social and economic effects that we can avoid by strengthening our City's skeleton—our buildings—and protecting our communities."
The ordinance is based on a portion of the findings in Resilience by Design, a report issued in 2014 by the mayor's office and created under the leadership of Lucy Jones, Ph.D., a seismologist and science advisor for the U.S. Geological Survey who served as the mayor's advisor for seismic safety for the report. (See "Preparing for the Big One" by Catherine A. Cardno, Ph.D.,
, February 2015, pages 70-75.)
The ordinance applies to all soft-first-story wooden buildings—exclusive of those built for solely residential purposes and containing three or fewer units—and all wooden buildings built to building code standards that were enacted before 1978. Examples of soft-first-story wooden buildings include small parking structures or commercial store fronts, according to the Los Angeles Department of Building and Safety (LADBS). Without proper strengthening, these types of structures are prone to structural failure during earthquakes.
Nonductile concrete buildings—exclusive of detached single-family homes or duplexes-that were built to codes enacted before 1977 must also be retrofitted under the new ordinance. Such buildings have a limited amount of reinforcing rebar in their columns and walls. Under the types of large lateral loads that can occur in earthquakes the columns and walls tend to break apart, enabling the buildings' stories to progressively collapse onto one another as the concrete spalls and the columns and walls weaken.
Under the ordinance, seismic retrofits of the wooden structures must occur within 7 years, and retrofits of nonductile concrete structures must take place within 25 years. Within those time periods are milestones that owners must meet to show that they are taking steps to have their buildings assessed and, if deemed necessary, strengthened.
According to the mayor's office, the LADBS has identified approximately 13,500 soft-first-story buildings that must be assessed and potentially retrofitted under the new ordinance. Approximately 1,500 nonductile reinforced-concrete buildings were identified as meeting the criteria of the ordinance, according to a study released last year by the University of California, Berkeley, and cited by the mayor's office during the signing.
The Structural Engineers Association of Southern California (SEAOSC), based in Los Angeles, has a long history of working with the LADBS, which oversees the building permitting and now the retrofitting efforts within the city, according to Michael Cochran, S.E., SECB, M.ASCE, a vice president in the Marina del Rey, California, office of the engineering firm Thornton Tomasetti Associates Inc., and a member of the mayor's Seismic Safety Task Force, which helped create the
Resilience By Design
"SEAOSC has been assisting the building department with the technical side of the retrofit ordinance as well as developing some design examples for both the wood soft-story and nonductile concrete buildings covered by the ordinance," Cochran says. "SEAOSC has a long history of working with LADBS in developing the technical criteria for local seismic retrofit ordinances dating back to the 1980s."
Building owners' support of the ordinance as a safety measure is tempered by concerns about how the seismic retrofitting will be funded. The Los Angeles office of the California Apartment Association supports the idea of the mandate but as an organization is concerned with how the retrofitting costs will be borne by the typically mom-and-pop owners of such soft-first-story structures as modest-sized apartment complexes, according to Beverly Kenworthy, the office's executive director.
The Building Owners and Managers Association of Greater Los Angeles (BOMA/GLA), which focuses on the interests of commercial owners of nonductile concrete buildings, issued a statement about its support for building resilience, tenant safety, and the mayor's work to ensure seismic retrofitting. A representative from the organization—Martha Cox-Nitikman, the vice president of public policy—also testified in front of the city council during the week that the ordinance was passed, noting BOMA/GLA's appreciation of the fact that a number of its concerns had been adopted into the ordinance and expressing its interest in continuing discussions as the ordinance is implemented.
The statement of support for the ordinance issued by the SEAOSC echoed the funding concerns, noting that the cost and inconvenience of implementing seismic retrofits of vulnerable buildings can be daunting, especially when weighed against the generally rare occurrence of major earthquakes. "Any government retrofit mandate must give careful consideration to costs associated with construction and interruption; but we believe these cost considerations should not be allowed to outweigh the importance of public life-safety, personal and community resilience, and continued regional economic viability after the next major earthquake," SEAOSC's statement reads.
The SEAOSC makes the point that the costs of recovery from an earthquake that has damaged or destroyed buildings is far greater than the cost to retrofit the buildings to withstand the quake before the event. "It has clearly been demonstrated that it is far cheaper and more economical to strategize in advance and start to allocate resources to begin retrofitting [or] strengthening buildings and the infrastructure prior to the next event as opposed to waiting [until] after the event," Cochran says. "After the event there is typically an extreme shortage of labor and materials; costs are two, three, or more times [higher] than normal to complete repairs; and wait times to accomplish the work [can] take months and years, where previously the work could be completed in far less time," Cochran says.
And while repairs are taking place residents may abandon the region, leading communities to struggle economically for decades as they try to recover, according to Cochran. This is precisely the issue currently facing New Orleans as a result of its Hurricane Katrina-induced levee failures, he notes.
Los Angeles, on the other hand, is working hard to improve its building stock before the next disaster strikes, in a quest to become a community that is as resilient as possible when that event occurs.
The new seismic retrofit ordinance applies specifically to building stock in the city of Los Angeles, although there are approximately 70 other jurisdictions in and around the Los Angeles basin, including those in the counties of Ventura, Los Angeles, and Orange, that could potentially adopt similar requirements, according to Cochran. "Some will take a wait-and-see approach at first, looking to see how the program works for Los Angeles City," Cochran says. "Some of it will be dependent upon the size of the jurisdiction and whether they think they can handle implementing such seismic retrofit requirements."
Cochran is quick to point out that the experience in the city of Los Angeles shows how engineers and engineering associations can participate in strengthening their own local building codes. "I think the best things the structural engineering organizations can do is start talking with the local leaders—the mayor's office, the city council members, as well as the various building owners associations," he says. "Both the public and private sectors have to be part of the conversation, discussing the economic impact on their region due to a natural disaster such as earthquake, hurricane, flood or inundation, tornados, et cetera."
Cochran also encourages structural engineers to be "the driving force" in helping to create task forces to explore what is needed to improve the nation's building stock and infrastructure. "The structural engineering community can provide the technical expertise, while the public jurisdictions and private business sector work out the administrative and economics issues of implementing the task force findings," he says. "Persistence is going to be what it takes to make this happen over the long run."
And it is persistence, and hard work, from both the public and private sector that has enabled the city of Los Angeles to reach this point in its efforts to ensure the life safety of its occupants when the next earthquake hits.