Quake-Revised Building Codes Await True Test
The last of a series of building code revisions based on the 1994 Northridge earthquake is expected to pass this month, making Los Angeles, already considered among the world’s most quake-ready cities, even more prepared.
But is it enough? Among the small group of people still pondering the Northridge earthquake, there is fierce disagreement over how well its lessons have been taken to heart.
Historically, changes made to the building codes of the city of Los Angeles after quakes “have saved so many lives, it’s really a great success story,” said Thomas Heaton, a Cal Tech professor of engineering seismology. “But at the same time, the range of things Mother Nature can throw at you is pretty big. . . . We don’t really know what to fix.”
Perhaps the most studied earthquake in history, Northridge produced reams of data and stacks of reports but has yielded fairly modest changes to codes so far--especially as they apply to existing buildings.
Of the dozens of changes the city has instituted since the quake, only a few have had or will have dramatic, immediate effects.
They range from aggressive measures requiring owners of hundreds of buildings to do repairs or retrofits, to deceptively minor amendments, such as one requiring designers and builders on the same projects to actually talk.
The strictest new ordinances target two types of buildings: concrete tilt-ups and steel-frame office buildings.
Owners of some 2,000 concrete tilt-ups built before 1976 must complete mandatory retrofits due to a rule passed immediately after the Northridge quake.
The buildings are mostly commercial and industrial structures, made by pouring concrete on the ground to form walls that are then tilted up and tied together. The buildings are considered hazardous because the walls tend to pull out, causing roof collapses during quakes, building officials said.
So far, some 1,300 tilt-up buildings are in some stage of retrofit or demolition, said Tim McCormick, structural engineer for the city’s Building and Safety Department.
Steel-frame buildings, which had previously been thought to be among the least vulnerable, pose a more complicated problem.
The Northridge quake showed they were flawed: A lower-cost weld that had come into vogue in the 1980s had tended to crack, meaning the buildings’ skeletons weren’t flexing to absorb energy, as they were supposed to.
Virtually everyone was caught by surprise. “The entire engineering community was freaking out,” said Martha Cox-Nitikman of the Building Owners and Managers Assn.
The city passed a controversial measure requiring that owners of 243 such buildings within a specified quake zone inspect their buildings and fix cracks if they found them.
The ordinance has had an effect, but progress is slow. With deadlines for repairs past, 217 have been inspected or are in some stage of repair. Confirming fears, about 60% were found to have cracked joints, McCormick said.
The experience highlights some of the dilemmas with retroactive codes.
Prior to the Northridge earthquake, the city had required owners to retrofit existing buildings only once, in 1981, when changes were ordered in unreinforced masonry buildings.
That debate pitted City Councilman Hal Bernson against hundreds of landlords who didn’t want to do retrofits.
Bernson won. When the Northridge earthquake hit, most of the 8,000 retrofits were complete. Without those repairs, experts said, the Northridge death toll would have been higher.
But in other areas, the payoff is not so clear.
Seismic safety codes in general are a problematic mismatch between economic necessity and the murky world of earthquake science.
In the case of steel-frame buildings, there was disagreement about both the seriousness of the threat and the best way to fix the welds. To compound the problem, the program is very expensive, costing owners about $5,000 per joint for weld inspection and $10,000 for repair.
It was a politically sticky situation for the city. Some building owners think they were punished for having deep pockets while more-dangerous buildings were given lower priority.
“When you talk about loss of life, there are so many other buildings that need to be dealt with,” said Cox-Nitikman. “Why isn’t the state doing something to help building owners, going from the most risky buildings to the least risky?”
But others such as construction attorney Joel Castro, who represented families of those who died in an apartment collapse, call the city’s response “laughable.” Pointing out that no inspections were required in tall buildings downtown, or in residential steel-frame buildings, he argues that severe hazards remain.
“I don’t know what it is about people, what it is about society,” Castro said. “Everyone says, ‘Well, it’s political.’ Well, it’s life!”
The measures taken to address the steel-frame building problem contrasts with the city’s response to another problem: non-ductile concrete buildings, such as some parking garages, stores and older hotels.
These older, concrete-frame buildings are considered potentially very dangerous in a big quake, structural engineers contend. In terms of potential hazards, “Non-ductile concrete buildings are right at the top of my list,” said Nick Delli Quadri, senior structural engineer with the city. Fred Turner, staff structural engineer with the state Seismic Safety Commission, was more blunt: He calls these buildings “killers.”
But repairs are very expensive, often more than $100,000 per building. So far, the city has set only voluntary standards for owners to follow.
Building officials want a stricter ordinance. But nearly all sides agree it would be unfair to owners to require such expensive retrofits without offering some government-backed financial incentives.
So, of the more than 2,000 such structures in the city, fewer than 100 have been retrofitted, McCormick said.
Most other building code changes made since the Northridge quake have taken the same form, setting only voluntary standards for existing buildings rather than requiring retroactive changes.
A Northridge-inspired voluntary retrofit ordinance for single-family homes has prompted 5,000 owners to bolt houses to their foundations, city officials said. That still leaves some 182,000 homes at risk, but building officials believe that with time many more people will comply of their own accord, or if prompted by insurance companies or banks.
The city is hoping the same will happen with a voluntary ordinance calling for retrofits of so-called “soft-story” apartment complexes, scheduled to be considered by the City Council next week.
These are buildings with tucked-under parking or weak shear walls in the first and second stories. The Northridge Meadows apartment complex, where 16 people died when it collapsed in the earthquake, was in this category.
City officials have high hopes that a number of other less-noticed changes in codes will make big differences in the city’s ability to withstand future quakes.
For example, buyers of new homes are required to install gas-valve shut-offs to help prevent fires after a quake.
One seemingly minor change requires designers of buildings to meet and talk with the construction contractors who build them.
The measure was a response to numerous quality-control problems found in buildings after the quake--including Northridge Meadows.
“We can have the best design backed up with the best analysis. . . . But when it actually gets built, it can be a totally different animal,” said Saif Hussain, a Canoga Park structural engineer. “This forces all of us to sit and talk.”
Several structural engineers said the new rule has helped them catch potentially serious mistakes: nails that were too small, washers left off, straps incorrectly installed. Such details can defeat the strictest building code.
The requirement increases costs, but “you become a better engineer,” said Bill Nelson, a structural engineer in Irvine. “You don’t work in a two-dimensional world anymore. You work in a three-dimensional world.”
But it remains unknown how much any of this will matter if the area is ever hit by the much bigger quakes expected by seismologists.
Northridge “was a moderate earthquake by earthquake standards,” said McCormick. “That’s why we are all so worried. The fact that there were so many problems in a moderate shaker is warning for the big one.”
Little is known about how to prepare buildings for that earthquake, and even less about when it will come.
“We work in what we call a ‘fuzzy’ environment,” said structural engineer John Kariotis of Sierra Madre. “We don’t know anything very well.”
People have a hard time dealing with these unknowns, said Lucy Jones of the U.S. Geological Survey. A prominent local seismologist, she has received letters from people accusing her of knowing--but refusing to reveal--when the big one is coming.
“You have to factor in this emotional reaction to earthquakes,” she said.
When it comes to making policy based on such unknowns, the problem invites contention.
On the one hand, “You might as well just assume it’s going to happen,” said Cal Tech’s Heaton.
On the other, Kariotis said, warnings of the Big One are overblown.
“Ask how many dollars you should invest to get maximum benefit,” Kariotis advised, “and don’t try to chase this thing of zero damage.”
At the moment, McCormick said, earthquake codes are only loosely related to calculations of the size of future quakes.
More important, he added, are the lessons learned from past quakes, coupled with the desire to save lives through the most cost-effective means.
“You can call the building code a history of man’s mistakes in construction,” McCormick said. “I know there is not enough money to fix it all, so you just say, ‘What can I do? Where’s the best place to put the money?’ ”
Despite these limitations, many of the city’s code amendments since the Northridge quake are being used as the model for new international building standards being developed for the year 2000, said Ben Schmid, a Newport Beach engineering consultant. It proves the city’s response “has gone extremely well,” he said. “No other city has come up with these ordinances so rapidly.”
Even those experts who praise the city’s response to the quake said more could be done. Future changes, though, are likely to come much more slowly.
That’s because there is a sense that political momentum to force change has ebbed. Most of the public seems more concerned with the possibility of an El Nino rainstorm tomorrow than a giant quake two generations hence.
“Suffice to say, the window of opportunity has closed,” said Turner, of the state Seismic Safety Commission. “That’s the political reality.”