Has Enough Been Done Since the 1994 Quake?

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-prepared cities, even more so.

But is it enough? Experts pondering the Northridge earthquake disagree 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 Caltech 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, the Northridge temblor produced reams of data and stacks of reports, but it 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 to each other.

The strictest new ordinances target two types of buildings: concrete tilt-ups, a common warehouse design, and steel-frame office buildings.

Owners of about 2,000 concrete tilt-ups built before 1976 must complete mandatory retrofits because of a rule passed immediately after the Northridge quake.

The buildings are mostly commercial and industrial structures, made by pouring concrete to form walls on the ground 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, about 1,300 tilt-up buildings are in some stage of retrofitting or demolition, said Tim McCormick, structural engineer for the city’s Building and Safety Department.

The city then turned its attention to a more complicated problem: steel-frame buildings, which had been thought to be among the least vulnerable.

But the Northridge quake showed that they were flawed: A lower-cost type of weld that had come into vogue in the 1980s had tended to crack, meaning the buildings’ skeletons weren’t working as they were supposed to, moving flexibly to absorb energy.

Experts were 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 structures and fix cracked joints if they found them.

The ordinance has had an effect, but progress is slow. With deadlines for repairs past, 217 buildings have been inspected or are in some stage of repair. Confirming fears, about 60% were found to have cracked joints, McCormick said.

The problem highlights some of the most difficult dilemmas involving retroactive codes.

Before the Northridge earthquake, the city had only once required owners to retrofit buildings, in 1981 when changes were ordered in unreinforced masonry structures.

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 the repairs, experts said, the Northridge death toll would have been higher.

But in other areas, the payoff is not so clear.

Seismic safety codes are a nearly impossible 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 to inspect welds, and $10,000 to fix them.

It was a politically sticky situation for the city. Today, some building owners believe 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?”

Critics 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 asserts 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 contrast with the city’s response to another problem: rigid concrete buildings, such as some parking garages, stores and older hotels.

Those older, concrete-frame buildings are also potentially very dangerous during a big quake, structural engineers contend. In terms of potential hazards, “Nonductile 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 the buildings “killers.”

But the 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 would like a stricter ordinance. But nearly all sides agree that 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 concrete-frame 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 voluntary retrofit ordinance for single-family homes inspired by the Northridge quake has prompted 5,000 owners to bolt houses to their foundations, city officials said. That still leaves 182,000 homes at risk, but building officials believe that, with time, many more people will comply of their own accord, or be prompted by insurance companies or banks.

The city is hoping the same thing will happen with a voluntary ordinance calling for retrofits of so-called soft-story apartment complexes, scheduled to be considered by the City Council soon.

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 dramatic differences in the city’s ability to withstand quakes.

One seemingly minor change requires designers of buildings to meet and talk with the construction contractors that build them.

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. These are the details that can defeat the strictest building code.

But it remains unknown how much any of this will matter if the area is hit by the much bigger quakes predicted by seismologists.

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Lessons of the Northridge Quake

Under revised Los Angeles city building codes, existing buildings are made more earthquake-resistant.

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The city has ordered changes on two kinds of problem buildings. . .

Type of building: Tilt-Ups

Problem: Walls and roofs in these wood-and-concrete buildings are prone to collapse.

Remedy: The city has ordered that all older ones be retrofitted. To date, 65% are in compliance.

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Type of building: Steel Frames

Problem: Joints in these tall office buildings are prone to cracking.

Remedy: The city has ordered inspections and repairs for some. To date, 90% are in compliance.

. . .but has only suggested changes to many others considered vulnerable.

Type of building: Non-Ductile Concrete

Problem: These all-concrete buildings are prone to collapse and considered among the most vulnerable.

Remedy: New retrofit standards are in place, but compliance is voluntary. Fewer than 5% have been retrofitted.

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Type of building: Soft-Story Apartments

Problem: Weak first stories in these buildings are prone to pancaking. Sixteen people were killed in one such structure in 1994.

Remedy: New retrofit standards are about to be adopted, but compliance is voluntary. Very few of the 20,000 considered at risk have been retrofitted.

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Type of building: Single-Family Homes

Problem: Foundations and walls are prone to cracking.

Remedy: New voluntary retrofit standards have prompted perhaps 3% of owners to retrofit.

Source: L.A. Department of Building and Safety