Years ago, while discussing what wind force a structure needed to endure, an old engineer told me a good rule of thumb for construction in the area was 50 psf. I then asked him about round columns. He answered the force is calculated by halving the area, if it was a square column. Otherwise, a column 4 feet in diameter will endure the same force as a square column 2 feet wide.
It doesn't sound like a lot of pressure, but I looked up a formula for determining wind force, built a small spreadsheet, and loaded some numbers in the formula. I was a little surprised, since a wind speed of a 140 mph is a hair over 50 psf. That's the wind speed of a category 4 hurricane.
After fiddling around with different numbers, it didn't take long to understand a 40 mph wind gust is much more of a force than most people envision. A 4 x 8 sheet of plywood exposed to a 20 mph wind has 32 pounds of force against the sheet. Of course, that doesn't calculate the complexities of the sheet shifting, or change in direction to the wind, but if it is suddenly hit with a 40 mph gust, the force against the sheet is now 165 pounds. That's definitely more than I can handle, and if I was in that situation, I'd have to let it go, and give up the project until the wind dies.
Locally, two major hurricanes pretty well removed the structures that can't handle hurricane force winds; especially at the local beach. Rebuilding required adhering to codes, and grandfathered structures disappeared. The result was higher insurance rates, the loss of family properties, and a better understanding of why they want people to evacuate from the storms. I've stayed through one, knew after it started I was in for the ride, and regretted staying. There was no fleeing in a wind force that can blow your car off the road. Even reaching the car is a gamble, and if you're hit with flying debris, they'll probably add you to the list of the dead.
Over here in NYC, Superstorm Sandy caused massive flooding to coastal areas, especially The Rockaway Peninsula. Houses and other structures were completely destroyed.
ReplyDeleteThe City changed the Building Code to require new structures to be on stilts so they would survive a Sandy-type flooding. A professional engineer friend of mine that was working on the design new homes in the area called me to ask if I foresaw a problem with wind loads, and the answer was “yes.”
With the house on stilts, the overturning moment on the foundation in an 85 MPH wind, would have overturned the houses. He alerted the building department, and that problem was solved by changes to the Code.
Bolivar Peninsula had large sections where only a few stronger posts were still visible. The homes built over decades without a strict code ended up on the north end of Galveston Bay as large piles of debris. The newer construction calls for substantial, large timbers, or concrete, and a minimum elevation of the bottom of a structure to be 16 feet above sea level. It increased the price of building, removed many from affording such homes, and will mostly eliminate the damage caused by a hurricane.
DeleteI remember Ron White talking about that in one of his stand-up routines.
DeleteA guy in FLA was talking to the news about him being able to tie himself to a tree and survive the hurricane (or something close).
Ron reminded everyone that it's not the wind so much as what the wind is carrying.
Something like............'Sure, you can probably survive a 90M PH wind, but not the Volvo it going to throw at you.'
Found it:
https://youtu.be/S7Fu-v490-c?si=rm4vlJREVwT2J3ti
My father worked for a shipping company on the coast in the early sixties. When Audrey hit the coast, some of the workers stayed to do what they could. A 2 x 4 pierced one of the workers, which led to a long stay in the hospital.
DeleteYup. Biggest winds I've ever been through? Texas.
ReplyDelete