Not many of us get too scared of a tusnami on the West Coast, but if you ever do, Cannon Beach, Ore., wants to be ready. And it may just well be on the right track.
The small, highly touristy coastal town on the coast strives to create the first tsunami-resistant building by 2014—a City Hall—in North America, but engineers must finalize necessary details first. You see, getting designs ironed out for an event that hasn’t materialized here in recorded history can be a bit of a challenge.
Jay Raskin, former Cannon Beach mayor and architect of the proposed building, elevated the design of the structure 18 feet by using 26 individual 3-foot diameter steel-reinforced, post-tensioned concrete pylons.
He says that having a government building withstand both a local earthquake and ensuing tsunami with room for 1,500 residents provides immense psychological benefits to the town. Getting it to survive takes another step.
Earthquakes rattle before tsunamis rush. Kent Yu, an engineer at Portland, Ore.,-based Degenkolb Engineers assigned to the project, says that normal FEMA earthquake standards come first. "If the building is leaning, nobody's going to go in," he says. "We need to make sure the building remains plumb." Yeah, that sounds like a pretty decent first step.
But more scary than just the waves, Yu and Dan Cox, a wave researcher at Oregon State University, say that debris pushed by the waves raises the biggest concern. Open columns negate hydrodynamic force, but the impact load from floating debris remains "a big deal" as the base sheer goes up with increased debris damming, Cox says.
"This force is horrendous," Yu says. "A typical log, when it hits the concrete column, is at 100 kips. That is a huge amount of force and we need to make sure the columns can resist the impact loading."
Waves are frightening, but waves carrying large trucks, twisted steel (no, not cows such as in the movie Twister) and other daunting debris takes frightening to a new level.
To reduce the load impact, solutions may include 6-foot walls on the property's edge. "What does that do in terms of reducing wave loads?" Cox asks in his ongoing research, something that needs ironing out before final designs get set.
Wave scouring will erode at the foundation, weakening the columns, so Yu plans a concrete-reinforced pile foundation (steel corrodes and wood is "flimsy"), with piles tied together. "Even if we have some scouring on the perimeter, the piles in the middle should stay intact," he says. "Piles connected together should help the interior of the building."
And because of the prospect of high waves—the building height plans for clearance at the 90 percent inundation level—pushing up on the bottom of the structure, Yu says that the building's concrete slab contains two mats of reinforcement.
While the superstructure, which may sustain acceptable beam cracking, plans for earthquake standards, research continues on local soils to determine the depth needed for the piles.
So while engineers work out the details and locals wonder about funding for this structure, let’s see if Cannon Beach can make waves of its own by getting this project up and off the ground. Literally.
