Just as there's no such thing as an earthquake-resistant building, there is no such thing as a building which is completely tsunami-proof. The Tsunami House on Camano Island, Washington, however, is arguably the closest thing to it.
The recently completed 3,140 square foot waterfront project designed by Designs Northwest Architects is capable of withstanding the impact of high-velocity wave walls with heights of up to eight feet, as well as a 7.8 scale earthquake and 85 mile per hour lateral winds.
Like many other structural engineering challenges, the unique problems associated with the project arose as a result of its location.
The Federal Emergency Management Agency (FEMA) flood zone required that the structure be elevated on concrete columns over the base flood elevation to allow the passage of water during a high water event such as a tsunami.
The typical approach to dealing with waves is based on a long-standing principle – take the path of least resistance. Instead of trying to resist the water pressure, the engineers simply let the waves flow below the structure with the least resistance possible. Since the owners wanted somewhat useable space below their house, any walls that were to be installed had to be strong enough to withstand the high wind pressures without failing, yet weak enough to simply break away during a wave event.
“It’s not often an engineer must design a connection to be weaker than a design force, and it went against everything I learned during my days in the University of Washington CE program,” said project engineer Jason Lindquist.
There were not enough walls to use conventional wood framed shear structures for all of the lateral force resisting systems, as the designers wished to preserve the tremendous view of the ocean and to utilise the footprint to provide as much living space as possible.
“Not only do we have a high wind exposure and high flood elevations – but Western Washington also has relatively high seismic forces,” explained Lindquist. “We therefore used two steel moment frames to laterally support the structure and to provide an open, beachside feel to the house.”
The third main challenge was the poor soil conditions, which required the geotechnical engineer to recommend the use of a raft foundation. Acting as a large distribution pad, the column forces were transferred into the supporting soils via the rigid foundation footing. The foundation selection over a deep pile system was chosen partially due to the location and difficulty of installing deep pile systems.
Lindquist believes engineers need to be realistic when it comes to designing buildings to survive extreme events.
“We try to model extremely complex natural events, such as earthquakes, using relatively simple mathematical framework,” he said. “On top of this, we have built the fundamental principles of the structural building code to be based on the statistical likelihood that certain magnitude events will occur over a specified period of time (i.e. the “100 year flood”).”
“In our own way, engineers have tried to balance designing safe, useable structures without going too far and over-designing for the worst possible scenario. For example, we do not design a house for the impact load of a vehicle running into the walls – although this is a remote possibility. I do not think we aim to build bullet proof structures that are mother-nature proof, I think our goal should be to protect life safety for events that are reasonably likely to occur.”
It is a beautifully elegant solution, but Lindquist does admit that this particular design would not be a viable option for low income regions, where the potential for such extreme events is greater.
“There was a large amount of concrete work that required close proximity concrete production facilities, as well as expensive formwork,” he said. “There was steel framing as well, which is very heavy and difficult to ship.”
Since the building’s completion, the architects have received enquiries from a potential client in New Jersey who is looking to redesign his property in the wake of Hurricane Sandy.
“Even though the buildings there use the same principle as the one we designed, they basically don’t do more than put a house on stilts,” said Dan Nelson, principal of Designs Northwest. “What we’ve shown is that you can make a home that can withstand disasters and also look beautiful.”