Answers about L.A.’s newly approved earthquake retrofitting law.
City targets its most vulnerable structures in new retrofit law
Los Angeles’ toughest-in-the-nation earthquake retrofitting law approved Friday focuses on two types of buildings: wood-frame apartments and brittle concrete buildings.
Making concrete structures better withstand a major quake is going to be the greater challenge. Refitting concrete will be much more expensive, and identifying what buildings need strengthening will be more difficult.
That’s the main reason why owners of concrete buildings will have 25 years to retrofit their structures once they are ordered to do so. Wood-frame apartments will have a seven-year deadline.
Certain types of old concrete buildings have long been considered to have the highest fatality risk in a major quake, and recent earthquakes have spotlighted their deadly potential.
A 2011 quake in Christchurch, New Zealand, toppled two concrete office towers, killing 133 people. Many of the 6,000 people killed in a 1995 earthquake in Kobe, Japan, were in concrete buildings. In 1971, the Sylmar earthquake brought down several concrete structures, killing 52. Twentythree years later, the Northridge earthquake wrecked more, including a Bullock’s department store and Kaiser medical office. How many potentially dangerous concrete buildings are there in L.A.?
Both The Times and university researchers have looked into the question.
In 2013, a team of Times reporters mined thousands of city and county records to identify older concrete buildings. The Times found more than 1,000 buildings in Los Angeles and hundreds elsewhere in the county that appeared to be concrete.
Researchers who study how concrete buildings fare in earthquakes say 5% of these structures typically collapse. In Los Angeles, that would be at least 50 buildings.
The Times then decided to take a closer look at a few select streets in seven L.A. business districts such as downtown, Hollywood, Westwood and Ventura Boulevard. They walked the streets looking for structures that appeared to be concrete. They pulled building permits and sent questionnaires to dozens of property owners, asking them to review the details. In these areas, The Times found 68 older concrete buildings, according to public records. Of those, just seven had been retrofitted, or strengthened to survive large earthquakes. The reporters’ work covered a fraction of the city’s older concrete structures.
The survey showed the difficulties of accurately identifying concrete buildings. Some city records didn’t specify the construction materials used. Some buildings that appeared to be made of concrete turned out to be steel-framed, and others that appeared to be brick or steel were concrete.
Not all of these buildings would collapse in a big quake. More studies would be needed to determine which ones are most at risk.
But reporting showed that it is possible for city officials to try to identify where brittle concrete buildings are located.
Before The Times’ survey, scientists at University of California and Cal State campuses began assembling a list of older concrete buildings for research, the first comprehensive attempt to catalog the scope of the problem.
After The Times’ story ran, the scientists eventually made the data public.
Their list is now the starting point for the city’s efforts to identify concrete buildings that need further study to see whether a retrofit should be ordered. How would that process work?
The city is still working that out, but it’s going to be expensive.
To determine whether a building needs retrofitting, owners may have to spend as much as $100,000 on a structural study that ascertains the inside of the building’s columns.
There are a couple of ways to strengthen the building if engineers conclude a retrofit is needed. They might install angled steel beams to provide more support, like an exoskeleton. Another solution could be the addition of sturdy interior concrete walls that stretch from the ground to the roof. The fixes could cost $1 million or more. Occupants probably would have to move out during the renovation, at an additional cost.
How long have we known about the dangers of concrete buildings?
In 1971, the Sylmar quake shattered two concrete structures at the 46-yearold Veterans Administration Hospital in San Fernando. The three-story buildings pancaked when the concrete crumbled, leaving the red-tiled roof smashed on the ground. Many patients were crushed under the debris; 49 people died.
Seismic experts were more alarmed by Olive View Medical Center in Sylmar, which had opened just months before the earthquake and was built using stricter codes. The fivestory hospital lurched sideways when some of its firstfloor columns broke. Three concrete stairwells toppled. A two-story psychiatric building collapsed. Three people died.
After Sylmar, L.A. officials beefed up seismic codes for new buildings, requiring more steel inside concrete columns to prevent chunks from breaking away. The extra steel acts like a cage, keeping the concrete in place even if the column cracks.
But structures built before the mid-1970s remain at risk because many lack adequate steel rebar and can’t bend. Engineers call these buildings “non-ductile.”
When more concrete buildings fell in the 1994 Northridge earthquake, Los Angeles Councilman Hal Bernson and Karl Deppe, a top city building official, decided the time was right to push for tougher retrofitting laws.
But those efforts failed to gain traction at City Hall.
Has Los Angeles had success with other types of seismic retrofitting?
Yes. Los Angeles was one of the first cities in California to require retrofitting of unreinforced brick buildings. Of about 8,000 buildings, almost all have been retrofitted or demolished after a 1981 law went into effect.
In some cases, Los Angeles officials had to go to court and threaten to label a building as unsafe, barring anyone from being inside it.
No one died from brick-building damage in the 1994 Northridge earthquake.