If you build your New Jersey beach house on stilts it has a better chance of surviving a hurricane and its storm surge. That’s obvious.
But how much better a chance than a house on a foundation? Can you measure it? How do you demonstrate it?
Those were questions Daniel Cox, an Oregon State University civil and construction engineering professor, and his research team were trying to answer with an experiment that culminated in a mini-hurricane Thursday at the Hinsdale Wave Research Laboratory.
Cox and his team built two 1/6-scale plywood houses. An airgun with staples and brads was used to assemble the houses, which were designed to resemble those on the Jersey shore. One was yellow and on a foundation. The other was orange and raised the equivalent of 5 feet above grade. Yes, the color scheme was intentional. And it also was clear that the yellow house was going down first.
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But it took awhile. The researchers started with small waves, which did not appear to be threatening the structural integrity of the houses. They then cranked up the pressure to waves that would be the equivalent of 4 feet on a full-sized house.
At that point yellow house already was showing signs of some distress and was missing some panels on its first floor. Orange house was pretty much intact, which surprised Cox.
It didn’t take the "4-foot" waves long to seal the deal. About five or six waves in, yellow house left its moorings and soon was buffeting about in the surf, leaving behind an extensive debris field.
Team members in waders and rubber boots got into the pool and used buckets and a fishing net to scoop up the remains of yellow house and brought it onshore for further study. Both houses contained recording instruments such as an accelerometer, a video camera, pressure gauges and a flow meter.
“There’s a lot of debris here,” Cox said, who also noted surprise at how quickly yellow house fell apart. “There was no sign that it was going to go … and then it was just gone.”
Orange house, meanwhile, stayed upright, weathering the storm surge with just a few of its first-floor panels revealing damage.
“We know elevated structures are good,” Cox said. “We just wanted to know how much better they were. And it was nice to be able to do (the experiment) side by side.”
Cox also noted that there were variables that must be considered when drawing conclusions. The age of the structure and materials corrosion are also factors.
“With different storm surges and different wave heights you get progressive damage,” he said. “Now, we’ll work up the results and try to figure out what to do going forward.”