Hawaii experts helping draft plan for tsunami-resistant buildings
By Eloise Aguiar
Advertiser Staff Writer
Tsunamis have the potential to flatten whole towns as demonstrated in Chile recently, but Hawai'i engineers are helping to create new building standards intended to prevent sweeping destruction here and elsewhere.
Structural engineers Gary Chock and Ian Robertson were in Chile recently on behalf of the nonprofit Earthquake Engineering Research Institute to survey the destructive power of a 30-foot tsunami that swept through coastal villages after the Feb. 27 earthquake, an 8.8 temblor. The earthquake generated a tsunami and together the two natural disasters caused 400 deaths in the coastal regions of central Chile.
"The town of Dichato was almost completely wiped out," said Robertson, a professor at the University of Hawai'i-Mānoa. "Fifteen hundred homes completely destroyed."
The earthquake triggered a tsunami warning here, but not much of a wave materialized.
But if a 30-foot tsunami were to strike Waikīkī, the receding wave would suck out sand and soil from under roads, beaches and buildings, toppling structures that lack a deep foundation, Robertson said.
And that's in addition to the destructive force of the wave.
It wouldn't be difficult to imagine containers and boats lifted on a wave into Downtown Honolulu, Chock said, with the potential to damage anything they hit. One boat in Dichato was carried more than a mile inland on the tsunami surge, he said.
"That's certainly a concern here in Hawai'i," Robertson said. "Particularly because our ports are our lifeline. In Chile if they lose this (Dichato) port, no big deal. Up the coast there's a much bigger port and it wasn't damaged."
Chock and Robertson are part of a team that has been working for four years on a National Science Foundation project to create U.S. design standards for buildings to withstand the effects of a tsunami. Six principal investigators, including Chock and Robertson, and a total of about 20 people expect to complete the design guidelines this summer.
What the pair found in Chile drove home the need for the new standards.
Robertson estimated that 4,000 to 5,000 people lived in the coastal village of Dichato but only 18 died because residents knew to get out at the first signs of an earthquake, he said.
The village's wood-framed homes and harbor were another story. Wood buildings crumpled and splintered under the 30-foot surge and subsequent waves that leveled everything in their path.
Even reinforced concrete and tile structures that survived the force of the wave were damaged because the water undercut their foundation, tilting them off balance and requiring substantial repairs.
Damage from scouring (undercutting foundations), debris and the sheer force of the tsunami devastated the tourist town that typically sees about 10,000 visitors in the summer.
Of particular concern was the damage to the port and harbor, said Chock, a principal in Martin & Chock Inc., a structural engineering company.
Buildings made of light metal, like some found at Honolulu Harbor, were smashed by shipping containers that were strewn about the harbor like Legos on a living room floor.
"A" AND "V" ZONES
"Honolulu is the only county in the whole U.S. that currently has some rudimentary tsunami design guidelines," Robertson said. But the standard is nowhere near the strictness of codes for wind and seismic activities, he said.
Basically if you're in the "A" inundation zone where you will get wet from a tsunami you must build on stilts, and if you're in the "V"(for velocity ) inundation zone those stilts must be able to withstand high-velocity water, he said.
"We're thinking the "V" zones should be larger," Robertson said, adding that parts of Waikīkī are in the "A" zone.
The new design standards will be much more detailed and take into account everything from the purpose of a building — whether it's residential or an evacuation center, for example — to new information about inundation compiled by UH professor Kwok Fai Cheung.
Cheung took historical Hawai'i-specific tsunami data and developed a model to update inundation zones, some of which are likely to be expanded.
Data about wave velocity, debris impact, uplift force, scouring effects of a tsunami and its impact force are being compiled and will be incorporated into the design guidelines as well.
"Current standard just gives one guidance for all buildings," Robertson said. "We're trying to differentiate between the different types of buildings and the different performance levels that we expect."
For instance, a small timber-frame residential home would include features that would withstand certain tsunamis but not the worst, he said. Meanwhile, a building that will be used for evacuation purposes would have to be designed to the higher level. Such a building would include such features as break-away sliding glass doors on the bottom level to allow water to flow through.
"As far as our design guidelines, if you can estimate the depth of the flow, the fluid coming through your site, that's what you need to start the design process," Robertson said. "Then we'll give the equation that will tell you what loads will be on the columns, the beams, the slabs and how to design the building for those loads."
Once the guidelines are completed they will be presented to the city and the American Society of Civil Engineers, which establishes standards for building construction, to be used in new buildings.
"We can't actually enforce them but we will try to get them adopted,"he said.