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May 9, 2017

Special applications: Resiliency

Photo courtesy of WACA
Staircases leading to the elevated roof platform are bolstered by 14-inch-thick, heavily reinforced concrete.

Ocosta Elementary School replacement

Location: Westport

Owner/developer: Ocosta School District

Team: Integrity Structures, general contractor; Vision Concrete, concrete contractor; TCF Architecture, architect; Degenkolb Engineers, structural engineer; Bayview Redi-Mix, ready-mix supplier

The new Ocosta Elementary School has the first vertical tsunami evacuation structure in the U.S. The elevated platform is capable of holding approximately 1,000 to 1,500 people.

That is important because if the Cascadia subduction zone — a 700-mile-long offshore fault in the western Pacific Ocean — were to produce a large earthquake, the resulting tsunami would be expected to slam into Westport and other parts of Washington’s outer coast. The people on the northwest coast would have about 20 to 30 minutes to get to safety.

Vertical-evacuation structures have to meet a lot of criteria, including being able to withstand the forces of an earthquake and, obviously, a tsunami. The foundation has to be strong and the structural supports need to be able to handle the forces of water and debris crashing into them.

The building must be constructed on deep pilings in case the tsunami scours out the foundation. The “vertical shelter” portion of Ocosta Elementary School is accessible from four staircases, one at each corner of the structure. The staircases are bolstered by 14-inch-thick, heavily reinforced concrete.

Even if the walls are ripped away, the cores should remain intact through both the quake and the tsunami, according to Cale Ash of Degenkolb Engineers, who designed the structure.

This was a significant and challenging construction project. It was a team effort involving project managers, supervisors and administrative staff, along with a team of hardworking subcontractors and suppliers.

We trust that the concrete structure will stand tall and save many lives should a serious earthquake and tsunami occur. Integrity Structures, TCF Architecture and the engineers who designed this school believe it will serve as a model for other evacuation structures.

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