Fearing that an earthquake is inevitable, Los Angeles city officials in October voted to enact the toughest seismic code in the U.S. It will require more than 15,000 buildings to undergo structural retrofits. “Non-ductile concrete buildings, constructed before the custom building code of 1976, have been exposed as very deadly,” says Jay Kumar, technical director at Partner Engineering and Science.
After spending a year searching for seismically inadequate buildings, city officials identified 13,500 soft-wall, multi-family wood buildings and more than 1,000 non-ductile concrete structures that need seismic retrofits. The Los Angeles Dept. of Building and Safety next month will begin the enforcement process.
“The city will be sending notices in groups to avoid putting too much pressure on the construction and engineering community [and] even the Dept. of Building and Safety, which will have a new plan-check department to monitor the ordinance,” says David Cocke, structural engineer at Structural Focus, Los Angeles. “It won’t be a random plan check.”
The new code results from criticism of the city’s inaction on earthquake preparedness. The Los Angeles Times published a 2013 report that identified over 1,000
concrete buildings as posing earthquake fatality risks. The Times said it began cataloging at-risk concrete structures after a New Zealand earthquake in 2011, when the collapse of two concrete buildings killed 133 people. “Time and time again, these buildings have proved to be extremely dangerous,” Cocke says.
Division 95 of the Los Angeles Municipal Code (LAMC) mandates upgrades for concrete structures built prior to the 1976 Uniform Building Code and any buildings with concrete floors supported by concrete walls and columns constructed under permits filed prior to Jan. 13, 1977, Kumar says.
Wood-framed, multi-family buildings that contain large areas of tuck-under parking that have a stability weakness at the ground-floor level—known as “soft-story” or “weak-story” buildings—built before 1978 are ordered to perform upgrades under Division 93, LAMC.
For the wood-framed sector, contractors with experience in steel erection, wood and steel-moment framing,concrete reinforcement, and concrete and steel connectors will be in demand as the city’s retrofit ordinance progresses.
Within one year, owners must perform a structural analysis and submit an engineered compliance plan to the city’s building department. The ordinance gives owners seven years to retrofit wood-framed buildings. “I think it will be good for business, sure,” Cocke says. “That’s a lot of retrofit design and engineering jobs, but I don’t think there will be any rush because of the length of the program.”
When upgrading concrete structures, contractors will deploy techniques and products that include base isolation, dampers, fiberglass jacketing, steel jacketing and reincasement of connectors, Kumar says. “Just an engineering analysis could take months,” he adds. The move is is expensive but, “in some cases, might be able to prove the building doesn’t need a retrofit,” he says. “The configuration of each individual building will dictate the construction applications used to comply, with wood-building upgrades ranging from $20,000 to $250,000.”
The process will be much more involved and expensive for concrete buildings, costing $50,000 to $2 million per retrofit. However, owners have 25 years to comply with the ordinance. Within 10 years, affected concrete buildings must submit detailed documentation of the building’s ability to comply without a retrofit, a detailed
structural upgrade plan or proof that prior retrofit work meets the new requirements.
With a limited number of contractors qualified to perform seismic work on the wood-framed and concrete buildings, prices could balloon. “The cost of the retrofits could rise as demand for contractors outstrips the supply,” Kumar says.
Cocke says the ordinance is written to allow for innovation. “The building department holds retrofit design work to the standards outlined in American Society of Civil Engineers 41-13: Seismic Evaluation and Retrofit of Existing Buildings,” he says.