Big Buildings Go Unchecked After Quake

Less than 20% of steel-frame mid- and high-rise buildings in Los Angeles have been inspected for possible damage caused by the 1994 Northridge earthquake despite evidence that the temblor weakened the buildings’ structural support.

There are about 1,500 such buildings in Los Angeles, but a Times survey of city records showed that only about 235 have been checked for damage to the welds that hold the big steel girders together.

Most of those inspected structures were in the San Fernando Valley, near the quake’s epicenter, because the Los Angeles City Council required inspections for possible damage.

A Federal Emergency Management Agency study of 185 Valley steel-frame buildings that were inspected after the 1994 quake showed that two-thirds had damaged welds. About half of the welds were cracked and the rest had more serious defects. Eleven percent of the buildings had damage to more than 10% of their connecting welds.

Chia Ming Uang, an expert on steel-frame buildings at UC San Diego, said it’s likely that other buildings around the city sustained some damage -- but officials don’t know because they were never inspected.

He and others said such damage might not become apparent until another major temblor strikes Southern California.

“The next time, we are confident that there will be damage,” he said.

In addition to the Valley buildings required to be inspected, city records show that about 50 owners outside of the Valley voluntarily had their properties checked.

That leaves about 1,200 unexamined steel-frame buildings, many of them in the downtown Los Angeles area.

The welds are critical because they keep the buildings structurally sound. Buildings can still stand if welds are damaged, but engineers said that numerous cracked welds can leave a building vulnerable in another moderate or strong quake.

Even in the cases where inspections were made, broken welds might have been missed. That’s because opening up every weld in a building for inspection would be very expensive and disruptive, so inspectors only spot-checked each structure, opening up connections where damage was suspected or in random corners.

“Those inspected and damaged after Northridge have been repaired in the spots where the damage was found,” said Nick Delli Quadri, head of the engineering bureau of the Los Angeles Department of Building and Safety. “But no one has retrofitted an entire building.”

The city has not pressed owners to upgrade their buildings because it would be exorbitantly expensive and officials do not believe that moderate earthquakes like Northridge will cause them to collapse.

“We’re pretty confident that’s not going to happen,” Delli Quadri said. “Look at the experience from Northridge. None of those buildings collapsed. They had some severe damage but none of them collapsed.”

The buildings of concern were constructed with steel frames in which the right angles of the frame are held together with welding material. Structural engineers believed this type of frame would be among the safest in earthquakes, because the steel, while strong, was flexible enough to sway with the earth’s movement and not break.

That type of frame was used for most high-rise construction from the early 1970s to the late 1990s.

But in both Northridge and the 1995 temblor in Kobe, Japan, welds that experts had thought would survive failed. It was a huge wake-up call.

For new buildings, structural engineers began to reconsider their designs and California changed its construction codes to require more earthquakeresistant welding materials. But there has been little pressure on owners to upgrade older structures.

Insurance companies lost so much money on steel-frame buildings damaged in 1994 that most changed their underwriting practices, said Alex Glickman, area vice chairman with insurance broker Arthur J. Gallagher & Co.

She said underwriters now run complicated scientific models of buildings that include various measures of earthquake vulnerability, including the type of construction, the age of the building and the proximity to known faults.

Premiums, she said, have increased. Additionally, some insurance companies and banks have required weld inspections when buildings change hands, though such requirements are still fairly uncommon.

“Everybody thought these buildings could not be moved,” Glickman said. “But they snapped.”

Seismic experts and others have been pressing government officials for more inspections.

“Every structural engineer will tell you they need to be inspected,” said David Cocke, a structural engineer and a spokesman for the Structural Engineers Assn. of Southern California.

But Cocke said the expense -- and the liability issues raised if a building is found to have problems -- have made retrofitting these structures a political hot potato.

“It’s a hardship to do the inspections,” Cocke said. “They have to go in at night when the offices are not occupied, they have to take down the ceilings and scrape off the fireproofing and look at them.”

If damage is found, the owners must then do the repairs or face accusations of negligence if the building collapses.

Some buildings have been retrofitted bit by bit over time, as they have changed hands or their owners embarked on remodeling jobs.

In 2002, for example, Equity Office Properties Trust took out permits to repair welds on the 10th and 11th floors of the 28-story tower at 550 S. Hope St. The permit said that the company wished to reinforce the structural steel on the two floors as part of preparation for other improvements. The Chicago-based company did not respond to a detailed request for comment.

Several of the region’s biggest developers -- including Maguire Properties, which owns the U.S. Bank building, and the Thomas Co., which owns Arco Plaza -- did not respond to repeated requests for interviews.

“Society needs to decide that it’s important to us to get rid of those buildings or fix them,” said James Malley, the structural engineer who conducted the FEMA survey of quake-damaged buildings in Los Angeles.

Without inspecting the welds on all 1,500 steel buildings, Malley and others said, the severity of the risk won’t be known until the next earthquake. Malley, past president of the Structural Engineers Assn. of California, is more concerned than city officials about the risk of building failure with another quake.

“If they are damaged, they may have been weakened, and the second one could take [one] down,” Malley said.

sharon.bernstein@latimes.com