Jim Lux wrote:
MTV wrote:
Jim Lux wrote:
MTV wrote:
Allodoxaphobia wrote:
On Sat, 07 Mar 2009 15:03:33 -0600, MTV wrote:

Thanks Jim,

Since I'm in far NW Harris County I'm in the "35 psf" zone, whatever
that is. Right on the coast is "45 psf."

Yes, we have hurricane straps.

As far as the max wind speed I trust the actual we had w. Hurr. Ike and
Rita. When Ike came back from the north, we were on dead on the eye of
the storm and locally measured 87 mph at IAH. It was 'winding down' at
that time, but still toppled huge trees all around. Just lost one on our
property, but just missed demolitioning one home. Of course, it was one
of those "100 year storms" that we've had three of now in 20 yrs.

The max vertical weight on the tower per leg is 8750 lbs so I doubt one
more guy would matter. Good advice on not using house bracket. My
thought was that it would be a safety factor when guys would be down
when raising the antenna. Of course, I wouldn't do anything with a
strong wind blowing.

I have two engineer son-in-laws that should be able to calculate per
modern stds.

Marv


most residential roof construction is mostly designed to use gravity to
keep the roof on and to support down forces. They don't resist upforce
well (unless you're in an area where the code encourages straps..
hurricane areas, for instance), nor do they resist side loads. The house
itself can usually take a fairly good side load (after all, there's all
that surface area exposed to the wind), but the fascia boards on the
roof can't, so you have a problem of transferring the loads from the
antenna/guy to the structure of the house.

Different areas of the country have different construction practices to
accommodate the loads that are important (e.g. my house in southern
California is designed to resist shaking loads in shear from
earthquakes, but I doubt the roof could take many feet of wet snow)


Watch out with 4 guys rather than 3.. The limiting thing on a guyed
tower is the downforce on the tower under load. If you have 4 guys, you
have more static load on the tower than with 3 (assuming you've
tensioned them the same), so you're that much closer to the failure
point. Glen Martin doesn't have a whole lot of useful engineering data
on their web site, so it's hard to even do a back of the envelope
calculation of the buckling loads on the vertical tubes.

And you gotta love the picture of a bunch of guys standing underneath
the tower they're tilting up without any sort of safety precautions.

Marv