[TowerTalk] Rohn 45 Bent Leg

[Grant Saviers]

An 80' self supporting tower I helped tilt up got bent on all 3 legs 
when a brace was put near the hinge point.  So we did what was 
mentioned.  Built a concrete form, drilled some dowel holes in the 
existing base, added some rebar and about a yard of concrete.  It stood 
for many years.  Not pretty, but the JA's won't see it.  I think this by 
far is the easiest, cheapest, and best short of replacing the whole 
section (which from your description is the section buried in the 
concrete??)  A guyed tower has very low loads on the base compared to 
self supporting, so you are just strengthening the bad section.

I wouldn't try the reinforcing the problem leg with a steel bar and 
u-bolts.  I don't think there will be enough slip resistance to 
re-establish the original leg strength. (or you will flatten the leg, 
just as bad)

RE welding:  R25 is hot dipped galvanized inside and out so obtaining a 
structural quality weld is very difficult.  Usually, parts go back to 
the galvanizer for stripping off all the old galvanizing before welding, 
then are regalvanized.  The legs are 50ksi yield steel, nothing special 
re the alloy and heat treating.

You should be using Rohn bolts.  You might have ok strength stainless 
depending what you bought and where you bought them. Drilling new leg 
holes at the correct angle, round and at the right diameter is not 
easy.  I've done it in a milling machine for making hinge pins and even 
then it was hard.  Now I make base hinge plates with the pins welded to 
them after they are bolted into the tower. Much easier.  Another fix is 
to make a bidirectional "adapter plate", i.e stubs in both directions on 
a 3/16 or 1/4" steel plate. I've done that for joining brand x salvaged 
aluminum sections to Rohn 25 for short field day towers.  A lathe is 
needed to turn the stubs to the leg inside diameter.

Re a crane lift: six sections are 6 x 41.1 lbs so way below what the 
bolt loads are in normal use, or with two folks on the tower.

Grant KZ1W




On 10/21/2016 9:05 AM, Dave Leisman wrote:
> I need some advice.  I have a 70' Rohn 45 and had a guy with a tractor back into and damage one of the legs.  As well, the leg was
> hit hard enough to bend the diagonal cross support.  I could probably, with assistance of a come along, bend the leg back into place
> and bend the diagonal support back into place as well, but that would not resolve the huge indentation which resulted from the
> contact with the tractor., e.g., the leg's strength would still be compromised.  There is no antenna on top of the tower; I was just
> getting ready to place my TH-11.  The tower is guyed at 30' and 50' at the current time.
>
> My thought is to rent a mobile crane with a boom long enough and significant enough to lift the 6 sections above the damaged section,
> in total (still bolted together) from the damaged section; then cut the damage away from the damaged section, and then lower the 6
> sections down to the now repaired section, drill all the holes and bolt everything back together.  Is this possible?  I am concerned
> about climbing the tower, because of the damage done to the leg - because somehow I need to strap the 6 undamaged sections to the
> boom of the crane.
>
> Another question is whether the stainless steel bolts holding the 6 sections together are sufficiently strong enough to hold the 6
> sections together while I work on the damaged section.
>
> I really don't want to start over because that means another hole to dig, expense of more concrete, placement of additional guy wire
> anchors (and more concrete), and waiting until late spring.
>
> Any advice would be appreciated.
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