[Towertalk] Tower Buidling 201 or How I Beefed Up a Wall To Which a Tower Is Bracketed (very long)
n4kg@juno.com
n4kg@juno.com
Wed, 4 Sep 2002 04:58:21 -0600
Interesting Story Jim, supporting my earlier statement
to "Never Say NEVER".
It IS important to note that your installation has ONLY 17 ft of tower
above the 'house bracket' vs. the 30 ft or MORE that unsuspecting
Tower Novices envision and want 'blessed' here on TowerTalk.
Tom N4KG
On Tue, 03 Sep 2002 22:15:59 -0700 Jim Smith <jimsmith@shaw.ca> writes:
> The following is quite long and is the work of a demented,
> anal-retentive paranoid.
>
> Ever since I joined TT 18 months ago I have been seeing cautions
> about
> house brackets. I have a flat roof with access from inside the
> house
> via a normal staircase. To accomodate the staircase, a structure I
> call
> "the penthouse" was built on the roof. Here's a view of the side of
> the
> penthouse while standing on the roof.
>
> ______
> / | <--- penthouse 7-1/2 ft high
> / _____ |
> / | | |
> / | | |
> / |door |
> / |to | |
> / |roof |
> _____/_______|___|_|_______roof level______________
> / _|
> / _|
> / | <- stairs
>
> The angle with respect to the horizontal of the sloping part is much
>
> shallower than what the keyboard allows me to portray. It is the
> same
> angle as that of a typical set of stairs. At the top of the stairs
> there is a small landing. When you reach the landing you turn
> right,
> open the door and step onto the roof. This was all done before I
> got
> back into ham radio after a many decade absence.
>
> All was serene until VE7IN, a former mentee and now a mentor (would
> that
> be remle and now elmer?) invited me to his QTH a couple of years ago
> for
> a mult-single "for old times' sake." Those who have read my
> subsequent
> stories on 3830 will know the details of how this led to my fall
> from
> grace into the hellish underground world of contesting. To seal the
>
> devil's bargain he gave me 2 10 ft and 1 5 ft section of Rohn 25G.
> Hmm... I still have a TH3 and Ham M plus some mystery mast from the
> old
> days. All I need to do is prop up the 25G somehow on the roof with
> the
> TH3 etc on top, hook it all up to the 75A-4 and 100V and I'm in
> business. "Not so fast," says 7IN. First of all, the old rig
> doesn't
> cut it any more so, if you're serious, get something decent. Sigh.
> Several K$ later I got a MkV. He was right.
>
> With respect to my idea of putting the TH3 on top of 25 ft of 25G
> sitting on the roof and attached to the penthouse with a couple of
> U-bolts he suggested I subscribe to TT before doing anything. "What
> do
> they know?", I asked in my haste to taste the forbidden fruit of
> contesting under my own call. "At least a hundred times more than
> you
> do," was the chastening reply. Nowhere have I read of Adam having
> to
> learn to calculate wind loading and overturning moments before
> indulging
> in that temptation which led to his expulsion from Zone 21 but, I
> suppose, modern times lead to modern torments.
>
> So, here is my house bracket story.
>
> Below is a plan view of the penthouse showing the location of the
> 25G.
>
> landing ____ o
> \ <--- 25G
> ____________________\_o___o_____
> | | \ ^ |
> | | | |
> | | beefed |
> | stairwell |<-- up -->| <--- top (plan) view
> | | portion |
> | | | | North ----->
> |__________________|______V______|
>
> ^
> |
> |
> door
>
> The 25G rests on the roof and is flush against the wall. The
> diagram
> shows some space between the tower and the wall. This is a
> limitation
> of what you can do with ASCII drawing. AutoCAD it ain't.
>
> From reading TT and doing some calculations it became evident that
> there is a risk of the tower prying the penthouse right off the roof
>
> (think of a giant claw hammer with the tower being the handle) so I
> decided to "beef up" the penthouse structure. Here's what I did.
>
> 1. Removed the drywall (gyproc, sheetrock) from the W, N and E
> sides of
> the to be beefed up portion as well as the ceiling. From here on
> "Beefed Up Portion" will be referred to as "BUP" (Not to be
> confused
> with BIP or BOP)
>
> 2. Bolted the sill plates of the BUP to the underlying roof joists
> with
> lag bolts every 16" wherever possible. Where there was no joist
> under a
> 16" run of plate I used a Hilti toggle bolt to anchor that portion
> of
> the plate to the 3/4" T&G ply which forms the roof. (Maybe the
> phrase
> "sill plates" is regional. I'm referring to the 2x4s which lie flat
> and
> which support the vertical 2x4 studs which comprise the frame of a
> typical wall.)
>
> 3. Bought some 1-1/2" x 1/8" angle iron. Cut it into 3" lengths
> and
> drilled 6 holes into each piece, 3 into one side of the "L" and 3
> into
> the other. They are now called brackets.
>
> 4. Placed a bracket on each side of each stud where it meets the
> sill
> plate and secured the brackets to the studs and sill plate with #8 x
>
> 1-1/2" wood screws. Did the same where each stud meets the top
> plate.
> Did the same with the ceiling framing.
>
>
> _______________________
> _______________________ <-----top plate
> | |
> | |
> | | <--- stud
> | |
> bracket ___ | | ____ bracket
> \ | | /
> \ | | /
> ______\|_|/________________
> ___________________________ <---- sill plate
>
> 5. Added a stud in the NW corner to fill in the gap left by normal
> corner framing practice.
>
> 6. Screwed (and maybe glued) all NW corner studs together at a
> number
> of places along their length.
>
> 7. Used metal framing connector plates at the NW and NE corners at
> the
> ceiling to rigidify the corners.
>
> 8. Added 2 2x4 studs to the West wall. These 2x4s are directly in
> line
> with the 25G legs. Brackets applied top and bottom here as well.
>
> 9. Added 2x4 X bracing to the W, N and E walls of the BUP as well
> as
> the ceiling.
>
> 10. Clamped 25G to the wall at the 1 ft, 4 ft and 6 ft 8" levels as
>
> follows, repeat for each level:
>
> 10a. Cut a 1-3/4" x 1-3/4" length of "purple heart" wood. (This is
> a
> very dense tropical hardwood. Anything else would work as long as
> what
> follows won't crush it and it won't swell or shrink with weather.)
> Let
> 2 U-shaped holes into one edge. The hole widths to be the same (no
> slop.... the same) as the diameter of the 25G legs and spaced the
> same
> as 2 25G legs. i.e. the wood length, when installed, will be
> horizontal, will fit over the tower legs and will clamp the 25G to
> the
> wall. (Do I see the Prime Director cringing? Don't worry, Steve,
> there's more to come.) The depth of the holes is such that the
> tower
> legs project past the edge of the wood about 1/8". The idea being
> that
> the 25G legs, once clamped into place, can't move without moving a
> bunch
> of other stuff, i.e. the wall. How long is the wood? The entire
> width
> of the wall in the BUP. In my case, about 4 ft.
>
> 10b. Cut a piece of 1-1/2" wide x 1/4" thick galvanized steel the
> length
> of the wood.
>
> 10c. Drilled 1/2" holes through the steel and the wood for carriage
> bolts. These bolts to pass through the wall such that they graze
> either
> side of the 2x4s behind the tower legs. i.e. when the bolts are
> installed there will be 4 of them on each level, one on each side of
>
> each 25G leg. See illustration below.
>
> 10d. Drilled 1/2" holes in 4 ft length of 1" band iron to match the
> carriage bolts. Filed holes square to accomodate square porion of
> carriage bolt heads. Length same as the purple heart. This will be
>
> placed against the studs on the inside of the wall.
>
> 10e. What about all that extra length of wood, steel, band iron etc?
>
> Drilled holes for lag bolts wherever there's a stud.
>
> 10e. Screwed and glued 1/4" plywood to W, N and E walls of BUP as
> well
> as ceiling.
>
> 10f. The big moment. Took two people. Pushed the already assembled
> 25
> ft of tower up against the wall. Placed the purple heart wood over
> the
> legs and the steel bar over that. On the inside, positioned the
> band
> iron and poked the carriage bolts through the holes. When done, the
>
> carriage bolts were locked in position in the square holes in the
> band
> iron and projected through the wall, the purple heart and the steel
> bar.
> On the outside, put a washer and nut on each bolt and tightened,
> but
> not real tight. See illustration below.
>
>
>
> o <--- tower leg (did you find
> the other 2?)
>
> 1/2" carriage bolts--->|-->| | <--|<--- 1/2" carriage bolts
> ___|___|______|___|___
> ___|___|______|___|___ <-- steel bar
> ___|_o_|______|_o_|___ <-- purple heart
> ___|___|______|___|___ <-- wall cladding
> ||2|| || ||
> ||x|| ||<||---- 2x4 stud
> ___||4||______||_||___
> ___|___|______|___|___ <-- 1/4" ply
> ___|___|______|___|___ <-- band iron
> 1/2" carriage bolts--->|-->| |<--|<--- 1/2" carriage bolts
> bolt heads ---> U U U U
>
>
> 10g. Plumbed the tower and installed the lag bolts through the band
> iron
> on the inside and into the studs.
>
> 10h. Tightened the carriage bolt nuts on the outside.
>
> 10i. Installed the lag bolts through the steel bar and purple heart
> on
> the outside and into the studs.
>
> 10j. On the inside screwed and glued 1/4" drywall to all surfaces
> but
> left a gap at the band iron slightly greater than the width of the
> band
> iron.
>
> 10k. Covered the gap with 2" wood trim such that the trim may be
> easily
> removed so I can get at the carriage bolt heads in the future
> without
> damaging the drywall.
>
> 10l. Painted the inside of the penthouse.
>
> So, I have a 25' tower clamped to the wall with about 17' of tower
> projecting above the penthouse roof. No guy wires. (This puts the
> beam
> at about 45'.) The clamps, being lagged to several studs and the
> studs
> being tied together by the X-bracing and the plywood skin screwed
> and
> glued to them on the inside, distribute the tower forces over a good
>
> chunk of wall. (Almost sounds like I know what I'm talking about.)
>
> Does it work? I've got the old TH3 tri-bander on the tower. A few
> months ago we had the worst wind in 25 years. Some (not all) 2 ft
> diameter trees on the boulevard lay right over leaving 5 ft deep
> holes
> where their roots used to be. I went up on the roof (it's flat,
> remember) to check out the tower. The top might have been moving
> laterally an inch or so, no more. The next day I checked the
> drywall in
> the penthouse. Not the slightest sign of a crack anywhere.
>
> There is no vibration/noise issue. I sleep really well at night
> and,
> more importantly, so does my wife.
>
> Hope this was of some intrest.
>
> 73 de Jim Smith VE7FO
>
>
> n4kg@juno.com wrote:
>
> >Here's another N4KG 'NEVER DO'
> >
> >NEVER use a House Bracket to support a non-self supporting tower,
> >unless you have at least one set of guy wires 30 ft or less above
> the
> >bracket.
> >
> >Besides the Vibration / Noise issue, if you get a really STRONG
> >wind and lose your tower, you will also have a HUGE repair bill
> >for your house.
> >
> >There is nothing STRONGER, SAFER, and more COST EFFECTIVE
> >than a PROPERLY GUYED TOWER.
> >
> >Note that for tower heights under 70 ft, Rohn shows a 35 ft (50%)
> >guying radius for their (discontinued) fold over tower
> intallations.
> >
> >Tom N4KG
> >
>
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