Reinforced Tower Leg
Reinforced Tower Leg
(OP)
So I've got an interesting problem. I've got a telecommunications self support tower where the legs have been reinforced by u-bolting a channel onto the tower legs.(I've attached 2 photos for reference) So from what I've seen, there's nothing that will allow the reinforcing channel to develop any of the compressive load that the tower leg is taking. I'm assuming the u-bolts are snug tight and as there would be no shear transfer there, the leg still takes all of the load. However, the with channel the overall shape is more rigid. So I was wondering if the following approach would be applicable of if I'm just a little outside the box on this one..
Pn= FcrAg
Fcr- I would use the composite member to calculate this... reductions as required for fastener spacing and all
Ag - Use the original 1 3/4" SR leg
So I'd be using the rigidity of the composite section to get my flexural buckling stress but I would only use the area of the leg as if unreinforced.
I'm thinking... either A) I'm oversimplifying.... B)This approach is already used and I've just never seen it... C) I'm a genius (this one is the least likely)
Thanks All
Pn= FcrAg
Fcr- I would use the composite member to calculate this... reductions as required for fastener spacing and all
Ag - Use the original 1 3/4" SR leg
So I'd be using the rigidity of the composite section to get my flexural buckling stress but I would only use the area of the leg as if unreinforced.
I'm thinking... either A) I'm oversimplifying.... B)This approach is already used and I've just never seen it... C) I'm a genius (this one is the least likely)
Thanks All






RE: Reinforced Tower Leg
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: Reinforced Tower Leg
RE: Reinforced Tower Leg
Mike McCann, PE, SE (WA)
RE: Reinforced Tower Leg
http://www.unistrut.biz/Literature/SeismicBracing/...
Need to check:
Capacity of the original member with braced length = U-bolt connection spacing
Capacity of the combined members for the full unbraced length. I would use Ag for only the original member as you noted.
Definitely oversimplifying because:
The bracing member is eccentric to the buckling member - not sure how to consider this. The buckling moment from the original member will place a small torsional load on the members (buckling reaction is eccentric to action).
Are the U-bolts tight? Will they remain tight?
RE: Reinforced Tower Leg
That's correct. With a reduced kl/r... my original legs will pass... essentially the rigidity of the channel will brace the SR leg. I just didn't know if this approach was appropriate.
RE: Reinforced Tower Leg
RE: Reinforced Tower Leg
RE: Reinforced Tower Leg
Check in TIA222G, but I think there is a provision to relax the KL/r ratio under certain conditions.
Been a couple of years since I investigated one of these towers, and I cannot remember the application clearly, but I know it does exist.
Mike McCann, PE, SE (WA)
RE: Reinforced Tower Leg
RE: Reinforced Tower Leg
Big help, huh...
Mike McCann, PE, SE (WA)
RE: Reinforced Tower Leg
If you were considering it a built up member we would also do a number of checks outside of tnx on the member as well, since tnx would only do a built-up check and not check each component of the member or anything regarding the connections between them.
RE: Reinforced Tower Leg
1) Radius of gyration = SQRT((I_leg + Iy_channel) / (A_leg))
2) Everything else the same as usual using the properties of the original leg alone.
Since the centroids of the leg and channel are located fairly close to one another, it's probably not much of a loss to ignore any potential for composite behavior.
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: Reinforced Tower Leg
another day in paradise, or is paradise one day closer ?