[TowerTalk] Rohn 65G Flange Question

[Grant Saviers]

I purchased 200+ ft of R65G old enough to need regalvanizing which I had 
done.  I don't know if it is "old" or "new" design, never heard of that. 
  All flanges were center drilled around 1"+.  A line thru two flange 
bolts bisect the center of the tower. The holes are there for liquid 
zinc to flow out when galvanizing plus drainage.  Now 142' of it is in 
the air with 8 large antennas.  The 60 ft left over is available cheap.

My view on the welds is if done to code by a certified welder only one 
on top of the flange is all that is needed.  Clearly heavy duty 
fixturing is needed to weld up these tower section.  Never had a problem 
other than cleaning zinc drops out of holes.  Use A325 lubricated (often 
blue colored) hot dip galvanized bolts, heavy nuts, and Nordlock lock 
washers. (McMaster)  Bring muscles and a torque wrench to the job. 
110ft-lbs lubricated; 220ft-lbs clean.

Two problems with painted towers are the paint needs stripped if you 
want to regalvanize and the inside is not painted.

My Rohn Unguyed book says unguyed R65 is limited at 90mph to 3.3sq ft at 
60ft.  There were no designs for higher wind speeds and I think this is 
pretty much the lowest wind speed now code required.

Grant KZ1W
Redmond, WA

On 11/19/2020 15:32, Byron Tatum wrote:
> Hello-    I am looking at around 200' of much older tower, from commercial service that has orange/white paint scheme on it. It appears identical to Rohn 65G in construction -- the leg size, zig zag brace size and pattern, and flange square dimensions. However, looking closer, these differences appear when comparing this older tower flanges with a marked 65G specimen:
>      1. The flanges on older tower are 1/2" thick (Rohn 65G is 5/8" thick)
>      2. The flanges on older tower are oriented differently -- they appear to be rotated 45 degrees as compared to Rohn 65G specimen.    3. I cannot find any part number stampings on this tower -- the Rohn 65G has part number stampings.    4. The flanges on this older tower are drilled in center to allow drainage. The hole size is around 5/8" on some sections and around 1" on other sections    5. The weld around tower leg on flange top on this older tower is not as "heavy" as the weld on Rohn 65G specimen.
> Here are my concerns -    I wish to use some 65G tower as a self supporter adjacent to my shop, in vicinity of 70 to 80 feet high with light antenna load. I plan to install it according to Rohn's drawings for this application, per the highest wind load specs/strongest installation. This would be a substantial base and lots of concrete/rebar. But I want to know I have the strength of 65G. I am trying to find out the particulars of this tower. Some knowledgeable folks have stated that it is Rohn, just an earlier version of 65G that was redesigned at some point and thus the flanges rotated on newer design to prevent mixing.
>      The one thing that concerns me is the welding of the legs to the flanges. It is said that Rohn welds the legs to the flanges both inside and outside. I noticed on Rohn 65G that the hole on flange is much larger. Does Rohn actually punch out a hole in the 5/8" thick flange plate and slide it over the leg, thus allowing this double-welding? This point here is the main thing in my mind in comparing the strength of the two different towers -- the older tower has thinner flanges and the flanges obviously are welded to legs only on the topside of flange due to small drilled holes as mentioned earlier.
>    Can anyone fill me in on this please.Byron W5FH
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