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telecommunication tower: lower leg reinforcement

telecommunication tower: lower leg reinforcement

telecommunication tower: lower leg reinforcement

(OP)
Tower leg is overstressed by around 10% and bracing can not be added nor reducing antennas loading.
any proposals?

RE: telecommunication tower: lower leg reinforcement

That doesn't leave many options! Can you strengthen the members? Can you encase in concrete?

RE: telecommunication tower: lower leg reinforcement

(OP)
Hi Ron
How to strengthen the legs at the lower panel noting panel is 3m and the legs are braced at 50cm interval
Regards.

RE: telecommunication tower: lower leg reinforcement

Add some steel to it. Or, as Ron says, encase it in concrete. Maybe if you give a bit more information about this tower leg you would get better answers. A picture or sketch would help.

RE: telecommunication tower: lower leg reinforcement

the tower leg is an angle section with toes facing inwards and the bracing connections are all on the inside, correct?
If so, you can stitch weld plates to the outside face of the angle legs, increasing the area and section modulus. should be a straightforward calculation to check the increased axial capacity. if the over stress is only 10% a 6 to 8mm plate should do it.

RE: telecommunication tower: lower leg reinforcement

(OP)
does this mean installing plates segments between existing bolts/nuts and above tower base shoe?
if so the leg will have non uniform section how to proceed/or may be I'm missing something?
Thanks

RE: telecommunication tower: lower leg reinforcement

Be sure to look at not only welding, but a bolted option for the leg plate reinforcement. Coax cable is know to be highly flammable and I've seen a few towers go up in flames due to welding. If the transfer of load can be accomplished primarily with bolts and just welding at the ends, I'd take that route.

RE: telecommunication tower: lower leg reinforcement

If this is a three legged tower, the legs are 60 degree internal angles, specially made by the tower manufacturer like Rohn or Valmont. If welding a plate across the legs it not possible, then fabricate an additional angle section to go over the outside of the existing leg and bolt them together.

Similar method for a four legged tower, only can use off the shelf angles.

Will gave to do some grinding for a tight fit...

Mike McCann, PE, SE (WA)


RE: telecommunication tower: lower leg reinforcement

The tower is likely HDG so, it's a matter of removing some of the coating and welding BAR material to the leg of the angles between the connection points. The new section is based on the reinforcing. At the connections because of the lateral bracing, you can check this as a steel section and not a compression element subject to buckling. Load capacity will approach As*fy*phi. It is then a matter of cleaning the welded areas and applying a zinc rich primer.

Dik

RE: telecommunication tower: lower leg reinforcement

A similar issue cropped up here a while back but I'm unable to dig out the thread. The answer seemed to be that the best reinforcement strategy was to sister a new structural member to the old one with some U-bolts wrapping around both sections. No welding, no bolting, no galvanizing touch up. There, I think that it ended up being another angle nested inside or outside of the original. The efficacy of the strategy would, in part, be a function of the particular failure mode that is governing your check. This setup works well for principle weak axis buckling. For torsional buckling, one might have to sister with a section that itself possesses some torsional stiffness. Or do something else.

Initially, what concerned me about this strategy was the relative impermanence of the set up. I've relaxed on that since. Really, any determined vandal with a wrench could probably find a way to disassemble one of these towers with or without reinforcement.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: telecommunication tower: lower leg reinforcement

would a problem area be to reinforce the leg below the two bracing elements ?

is it a column failure (which would be helped by mid-span reinforcement) or simple brute force (ie the ground reaction, which need to reinforce the ground attmt point) ?

It looks like a four poster to me (the far post is inline with the near one, but I think I can see the far footing).

Why is it impossible to add additional legs if reinforcing the existing legs doesn't work ?

How did this thing get to be 10% down ?



another day in paradise, or is paradise one day closer ?

RE: telecommunication tower: lower leg reinforcement

Is the tower in use all the way to the top? If not, chopping off the top above the highest antenna might help.

RE: telecommunication tower: lower leg reinforcement

(OP)
I looked at the complete survey photos there is a top MW.
Thanks any way

RE: telecommunication tower: lower leg reinforcement

(OP)
Dear Kootk
for the U bolts option do you have any references for such design
and references to verify U bolts size/spacing/etc..
Thanks for your time

RE: telecommunication tower: lower leg reinforcement

not my area but i'd've thought reinforcing the footings will be difficult.

is it unreasonable to add feet, like another four on a diagonal diamond pattern ?

another day in paradise, or is paradise one day closer ?

RE: telecommunication tower: lower leg reinforcement

My only "reference" would be the applicable steel design code. The strategy -- or at least one strategy -- is to cut down the unbraced length of the failing member so you'd probably have three U-bolts on the reinforced span: one at each end and one in the middle. Design the original member as braced at the U-bolts and design the bolts and reinforcement to be strong and stiff enough to do the job of being the bracing. AISC manual appendix 6 can help with that. I don't know transmission tower design codes so I'm unable to help there.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

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