When a hurricane strikes

A team of North Carolina State University researchers are testing new designs for ‘breakaway walls’ that could reduce damage to homes and buildings when a hurricane strikes.

Breakaway walls are designed for use on the ground floor of buildings in coastal flood zones. To minimise damage from storm surges, the US National Flood Insurance Program suggests that these homes and businesses be built on pilings, or ‘stilts,’ and that the ground floor be used only for access, parking or storage.

Property owners who choose to enclose this space are urged to use walls that will break away from the rest of the house when pressure exerted on them by a storm surge reaches a predetermined stress load — usually between 10 and 20 pounds per square foot. Stronger walls would absorb the force of the surging water, jeopardising the integrity of the entire foundation.

To determine what materials and designs will work best for breakaway walls, a trio of NC State researchers tested eight experimental wall prototypes.

Each 8 x 8-foot wood-wall prototype was tested in simulated hurricane storm surge conditions at a wave tank testing facility at Oregon State University. The researchers placed the prototypes into the tank, which measures 342 feet long, 12 feet wide and 15 feet deep, and directed increasingly strong waves and rising water levels at them until they broke apart.

Due to the size and depth of the tank, the researchers were able to test when and how the walls would fail in hurricane-force breaking waves, which exert an exceedingly high-pressure burst against walls as they crest.

Based on their findings, the researchers developed practical guidelines for builders to follow, such as using exterior siding no thicker than ½-inch plywood or equivalent material; using studs no bigger than 2x4s for breakaway walls; and placing the studs at least 24 inches or more apart.

Researchers Dr C.C. Tung, Spencer M Rogers Jr and Dr Bohumil Kasal also plan to test unreinforced hollow-cell masonry walls.

Because they sink, hollow cinder blocks are said to have the advantage of not becoming large, floating debris after a hurricane, making cleanup easier and reducing potential damage to surrounding buildings.

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