S.F. High-Rises Survive Quake With Only Minor Damage : Safety: Revised building codes and newer construction should keep tall buildings in San Francisco and Los Angeles standing firm after a stiff quake.
The gleaming skyscrapers that make this city the Manhattan of the West Coast survived the shuddering vibrations of the Oct. 17 quake with only minor damage, city officials and structural engineers say.
A Bechtel engineer who participated in a crash inspection program, as well as a Los Angeles city engineer, said the results should be encouraging for Los Angeles, where tall buildings are of more recent vintage.
The 52-story Bank of America building, built in 1969, received a mere $5,000 in damage. The landmark TransAmerica building, finished in the early 1970s, had minimal damage.
And the newer 101 California building, a recent glass-and-steel addition to the Market Street canyon, came through unscathed except for cracks in stairwell plasterboard and minor damage to a loading dock.
Frank Chiu, San Francisco’s chief building inspector, said as the high-rise inspection program wound down that none of the estimated 400 buildings taller than 75 feet that had been inspected since the quake, sustained major structural damage.
Only six received damage severe enough to restrict access, he said.
He attributed this to the city’s strict, updated earthquake code that mandates that buildings built under looser requirements be modernized and to a good enforcement team.
“That is why the high-rises could withstand this 7.0 quake,” he said.
Chiu led a team of city building and fire inspectors, supplemented by about 100 volunteer Bechtel Corp. engineers.
Concentrating at first on the buildings constructed before 1975, when building code amendments inspired by the 1971 Sylmar quake took effect, the inspectors looked for obvious structural problems, as well as damage to facades and jutting parapets.
While no major structural problems were reported, Bechtel Corp. engineer Jim Appleton said damage to the parapet on the old Channel 7 building on Golden Gate Avenue was visible from across the street. “Another shake and she would have come down on the building adjacent,” he said.
On Oct. 20--after completing inspections on almost all of the older buildings--the team began focusing on more modern buildings. The results from the first inspections of the modern buildings were even more reassuring.
At the 101 California building, the emergency power kicked in right after the quake, and the sprinkler system stayed in place. Nothing fell off the exterior.
“It’s amazing,” said Jim Barjioni, the building’s chief engineer.
Terry McGillivray, a Bechtel structural engineer who helped organize the volunteer inspector corps, said a number of factors contribute to the good performance of modern high-rise buildings under the strains of an earthquake:
- Because they are bigger, they are less likely to resonate in step with the typical ground vibrations that can cause a smaller structure to shake more and more violently.
- The steel frame construction, which can sway more than a foot at the top of a tall building, can absorb vibrational energy and is far less likely to fly apart, compared to load-bearing walls made of brick or unreinforced concrete block.
- Larger new buildings typically are engineered better than older, smaller buildings. Careful analysis of the soil underneath makes settling less likely.
McGillivray said a more careful analysis of the performance of San Francisco’s skyscrapers will be done, along with an examination of ground motions and stress calculations for specific structures.
In a few weeks, a computer will re-enact the quake motions of the 101 California building, which had seismographs in its basement as well as on the 8th, 24th and 48th floors.
McGillivray said his experience in inspecting San Francisco high-rise buildings has led him to conclude that Los Angeles would fare as well or better in a quake the same force of Tuesday’s in San Francisco. The Los Angeles code is similar to San Francisco’s for high-rise construction.
“For Los Angeles, with a newer skyline, you would be awfully surprised if there was any kind of damage at all,” he said.
“The more modern buildings that have been designed for more recent (building) codes should be good for larger earthquakes (than the Oct. 17 temblor).”
The Los Angeles building code is updated every three years, and requires minimum standards designed to save most lives but not prevent all damage in a quake the strength of the San Francisco temblor, said Doc Mghiem, an engineer in the city of Los Angeles Department of Building and Safety, earthquake safety division.
“We’re using basically the same code (as San Francisco), Mghiem said, and modifying it as needed, taking into account the condition of the soil, a building’s distance from known faults and its likely distance from the anticipated epicenter of a quake.
“High-rises (in downtown L.A.) behaved pretty well after the Whittier quake,” he said. “We would expect the same good behavior if we got a quake similar to the San Francisco quake.” Buildings would remain standing, he said, but ceilings and partitions would fall and business as usual could not continue.
Mghiem said the Los Angeles code is just the minimum required for basic safety and “in order to get a building behaving better than that, you have to do something better than barely the minimum. If a real big one hits, if ceilings come down--and they do come down--there will be some damage, some interruption of business and some destruction here and there, depending on how much above code the buildings were designed.”
Mgheim said the city’s priority for building quake safety in Los Angeles since 1981 has been on rehabilitating older high-rises where low-income residents live.
“The City Council is very concerned about giving the homeless something safe so they (don’t end up homeless again),” he said.
In a few weeks, a computer will re-enact the motions of San Francisco’s 101 California building, which had seismographs in its basement and on the 8th, 24th and 48th floors.
But Betty Brookes needed nothing fancy to tell her the building was shaking badly at 5:04 p.m. Tuesday--even though the damage was minimal.
An administrative assistant for Thomas A. Greene & Co. Inc., which has offices on the 46th floor of the 101 California building, Brookes said, “All of a sudden, things started dancing all over my desk. Things started popping out of the ceiling. The doors opened. The drawers slid open.”
Crouched under her desk, she said, she had the feeling that the top of the building was making a slow arc from side to side.
“It felt like we were swinging in space,” she said.
After the quake, she and others who had been in the office began the long climb down 45 stories.
About half way, she said, she met a woman who said she worked for a firm that analyzes how buildings perform in earthquakes. The woman told her that the building was one of the best in the state, as far as earthquake resistance was concerned.
“Yet it seemed miraculous that we weren’t under the rubble,” she said.
Free-lance writer Sheryl Kornman contributed to this article.