On May 7, 8:20*pm, "Robert Green" wrote:
"micky" wrote in message

...





On Tue, 7 May 2013 04:37:04 -0400, "Robert Green"
wrote:

We had a tornado 5 blocks away a while back and it scattered an entire
park
full of tall 2' foot wide oaks like pickup sticks. *If you are in the
direct
path of a tornado, no amount of bracing is going to help a typical
residential structure.

Not bracing, but I've heard that attaching the roof well to the top
floor of the house can greatly decrease the chance of the roof coming
off in a tornado. *That most roofs stay on by gravity and the nails
just help. *But where they've learned to use whatever they recommend
now, even in tornadoes the roof will likely stay on.

Agreed, but the OP was concerned about hits from trees, a different case
than having a roof lifted off by high winds. *Probably the only realistic
way to fortify a structure so that it can withstand a falling oak tree is to
build a steel roll cage around the house. *If cutting down all the trees
drops a home's value, imagine what a giant steel roll cage would do to its
"curb appeal." *(-:

One other point. *You've doubtless seen the swath a big tornado cuts. *Those
big twisters demolish wooden structures, roofs and all. *I still contend
that no amount of bracing or improved roof attachment is going to matter if
you're a stick-built house in the path of an F3 or greater. *It's sayonara
time for that structure as it gets pulverized and dragged into the next
county.

I agree. As I said previously, I can see addition roof connectors
helping
in the case where you're near the edge of the tornado path. But if
you're
directly in the path, it pretty much destroys the whole structure,
roof and
all. I suppose you could find some cases where it could have helped,
where there is a house or two, that for whatever reason was spared.
And if that house had the extra connectors, which is certainly a good
idea for any areas prone to extreme storms, then it could help that
house survive with it's roof intact. But in my view, that's the
exceptional
case.





I will agree that it's been proven time and again that good building codes
save lives. Florida's rules about attaching roofs has greatly lessened
damage caused by roofs flying off and then striking other homes and even
people with flying debris. *While it's still under investigation, that
recent collapse in Bangladesh probably wouldn't have happened if that
structure had been built better with adherence to building codes and better
inspection during construction.

http://news.nationalgeographic.com/n...bangladesh-dha...

The exact cause of the collapse has not yet been determined, but Henri
Gavin, a civil and environmental engineer at Duke University, speculated
that the building's foundation was substandard.
"It could be that one edge of the building was on much softer soil than the
other, so that part of the building settled down a little bit more," Gavin
explained. "That could easily lead to an instability that would precipitate
a collapse."

Another possibility is that weight on the top factory floors-where the crack
was spotted-was unevenly distributed. (Also see pictures: "Sinkhole Swallows
Buildings in China.")

I haven't followed this closely, but I heard reports around the time
it
happened that said the upper floors were added, perhaps illegally.
That has happened before, I remember a dept store in Japan, for
example, where they just added a floor without properly considering
the additional loads put on the rest of the structure.