Here are some before and after pictures of the Bolivar Peninsula.
I wonder what was different about the houses that remained standing?
Our house in Boca is just a few houses from the Intracoastal, on the mainland side, but the barrier island that separates us from the sea is a lot narrower than the Bolivar. I don’t know what kind of surge it would take to cross it and fill the Intracoastal and neighborhood canals, but I’ll bet a lot of the multi-million-dollar mansions on the ocean would get wiped out, or at least badly damaged in a similar situation. But they might help blunt the blow of the water and keep it from getting to us. A worst-case for us would probably be a similar west-bound storm hitting north Broward, around Deerfield Beach or Hillsboro, which would maximize surge up here.
[Update a while later]
Jeff Masters has more, on the almost total destruction of Gilchrist.
I don’t see any description of the type of construction. Our house is cement block on concrete slab. I can see a wood frame getting stripped off its foundation, but it’s pretty scary to think what kind of force it would take to empty our lot.
Even better are houses made using ICFs (Insulated Concrete Forms). The walls are essentially one unbroken, monolithic structure. Things are damned near indestructible. If I was having a home built from scratch, that’s the way I’d go.
Maybe some of the houses still standing are on stilts. Even if they weren’t before the hurricane (due to the presence of an easily washed out first floor). ICFs sound interesting. Should hold up to considerable wind, but I wouldn’t better on one withstanding the peak of a strong storm surge.
You wrote: “I can see a wood frame getting stripped off its foundation, but it’s pretty scary to think what kind of force it would take to empty our lot.”
It might be less than you might think – I think a lot depends on how the blocks are tied to the foundation. You know how much water weighs, and you can do the math on how much force is carried by three feet of water moving at ten miles (or more?) per hour. Add wave action on top of that. Don’t forget what could happen if the surge breaks through a window or door, and the wave action can do a back-and-forth number.
Karl, most of the houses in those pictures were on stilts.
I regret in advance the pedantry….
Concrete Masonry Units (CMU’s) can be tied together with steel reinforcing bar and grout. In principle, they can become forms for a reinforced concrete skeleton.
When a CMU wall has an opening (for a window or door), the steel / grout reinforcement supports the loads over the opening.
Also, the manner in which the wall gets tied to the foundation determines how well it resists shearing off the foundation.
If you zoom in close enough you can see that the pillars that hold the houses up are still there. it is just the frame the house that got sheered away from the pillars. The houses that till have their top levels just survived due to their relative height. The three building in the middle stand a full story higher than all those around them. This top story most likely just rose above the height of the storm surge.
I had a relative in Florida who lived right off the water in a Condo on the second story. A storm surge came in from a hurricane and totally wiped out the 1st floor and all that was left was the pillars holding the condo building up. I found that that the bottom floor or a beach front building in built in a way so that the walls purposely give away when a surge comes through. The pillars are left in place and their reduced surface area lets them stand up to the force of the water and insure that the the building as a whole stays standing. If the walls don’t give away then the pressure against a broad flat surface multiplies and can case the whole structure to list and fall over.