US engineers study Chile earthquake to bolster California building codes
Since the Chile earthquake, dozens of US engineers have visited Santiago and other affected cities to study the failures and successes of building codes here. They say it provides valuable insights for California.
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"This earthquake overall can be considered a success in terms of the engineering and construction practices in Chile," Mr. Maffei says.Skip to next paragraph
In Pictures Rebuilding after an earthquake
In Pictures More images of Chile's earthquake
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Preparing for tsunamis
In fact, more damage was caused because of inadequate storm preparedness. The greatest concentration of destruction and loss of life in Chile was the result of successive tsunami waves that denuded the coastline.
Eli Robertson, a professor of civil and environmental engineering at the University of Hawaii at Manoa, led a team of researchers here to study the performance of buildings hit by the tsunami. Mr. Robertson has been working on a National Science Foundation grant for the past four years trying to develop design building guidelines to protect from tsunamis. Hawaii is one of the few places in the US to have seen a significant number of deaths from tsunami impact.
"We need to know what to do with the folks in the coastal areas," Robertson says. "Do we tell them to go up in buildings and wait it out? Do we need to reevaluate buildings to include tsunami design?"
Here again, Chile provides invaluable lessons. Light-framed and masonry built homes stand little chance of surviving, but reinforced concrete frames performed quite well, Robertson found. Chile uses US codes for concrete design. By and large, these structures, though not specifically built for tsunamis, proved resilient to a 30-foot surge.
"We'll take some of the observations in Chile and compare them with what our design guidelines would say," Robertson says. "In other words, we'll try to design one of the structures we looked at and decide if it would have survived and compare that with what actually happened in the tsunami."
A forewarning for California
One immediate observation from Chile's earthquake that could find its way into US building code is on confining reinforcement, says Maffei, who is on the committee that decides building code in California. Confining reinforcement is meant to keep vertical bars from bucking, but the design proved insufficient in Chile. Maffei says he would consider requiring confining reinforcement along a greater length of the wall.
In preparing an earthquake-proof building code, engineers must also take into account the land the building sits on. Chile provides a case study in this, too. While the center of Santiago withstood the quake relatively well, on the outskirts of the city the metropolitan area of Maipu fared much worse because it sits atop soft volcanic ash, which amplifies the motions of the earthquake. Several apartment complexes in Maipu will have to be demolished.
In assessing these cases, according to Celebi, engineers try to correlate a building's design with the level of shaking. If the building was designed to withstand the shaking and damage still occurs, then there are two possible explanations: either the design is bad or the construction is bad.
Standing under Chile's mid-afternoon sun recently, Celebi considered two buildings positioned 90 feet apart. One was broken and leaning, the other was impeccable. The slumping building lacked sufficient shear walls, which restrict the relative displacement between floors. The design is widely used in Chile, and according to Celebi is probably what saved many buildings from collapse. This particular building, however, failed because the design didn't allow for sufficient support. Celebi shifted his attention to the building in perfect form.
"We have to appreciate the successes too," Celebi said.