Damaged slip-joint monopole shaft section - repair limitations?

[Ezra Shemuly]

Hello all
(apologies for the low resolution picture, the matter is out of my hands)

the question at hand is a section of a slip-joint monopole that was damaged during off-loading at the client's warehouse
the monopole was designed based on TIA-222-H and should comply to all relevant American standards and regulations

is there a limitation or rule that limits the client from trying to fix this damage and using the damaged section?
meaning - can I quote a specific paragraph in a standard (that I'm not aware of) that prohibits the use of such a part after it was repaired?

also - what is the relevant standard that outlines the acceptable tolerances for such a repair? assuming I cannot prohibit the usage of the repaired part?

thank you

 

[KootK]

Not my particular area of expertise but, since nobody's jumped in thus far:

1) I feel as though this ought to be repairable. Unless I misunderstand, the damaged area of the splice will function largely in tension (bending couple) which should be pretty forgiving.

2) I certainly don't know of any "thou shall not repair" clauses. And it would seem a market impropriety for their to be one in my opinion.

3) I also don't know of a tolerance spec. That said, for the top to fit over the bottom properly, you'd need pretty tight tolerances. So that might be self solving.

4) If there's a prohibition of some kind, I would guess that it would be aesthetic in nature. Who wants to spend top dollar on a fugly pole? Maybe the client does if the replacement would be on their dime.

 

[Compositepro]

The poles are tapered and one taper fits into the next taper. There should be no issue in banging out the damage. Taper to taper fits are tight when assembled.

 

[Ezra Shemuly]

Not my particular area of expertise but, since nobody's jumped in thus far:

1) I feel as though this ought to be repairable. Unless I misunderstand, the damaged area of the splice will function largely in tension (bending couple) which should be pretty forgiving.

2) I certainly don't know of any "thou shall not repair" clauses. And it would seem a market impropriety for their to be one in my opinion.

3) I also don't know of a tolerance spec. That said, for the top to fit over the bottom properly, you'd need pretty tight tolerances. So that might be self solving.

4) If there's a prohibition of some kind, I would guess that it would be aesthetic in nature. Who wants to spend top dollar on a fugly pole? Maybe the client does if the replacement would be on their dime.

thank you for your input
my concern is not esthetic, this is irrelevant in that specific monopole's location
purely from functional point of view - assuming the damage is in the male (internal) side of a splice connection - which should have very close fitting tolerance,
and remembering these are multi-sided (18 sides to be exact) shafts, so the bends should overlap for it to be able to slide one over the other,
I am struggling to vision how can this damage be repaired with enough accuracy in the warehouse, using hammers and dollies.
how can I be confident (as I am the designing engineer responsible for the performance and integrity of this monopole) that this splice connection will function as intended once the repair is done?

 

[TLHS]

I think I kind of agree with you here. I'd be worried about slop in parts of the connection and the dynamic stuff related to wind. Getting it back to the original shape to prevent that feels pretty tricky. Obviously some amount of damage is okay, but I'm not sure that I'd be comfortable deciding what the level of damage is.

Also, these are normally higher strength steels. Do you have an issue with ductility and cold reworking this thing?

 

[dauwerda]

I feel that if they got it close, tolerance would take care of themselves. The two sections are typically jacked together with large axial forces and will tend to move as needed.

I disagree with KootK's point number one about the force being mainly tension. The moment is transferred through the splice joint as a couple. The inside of the female section will be bearing directly against the damaged portion of this male section. If not straightened sufficiently, it could be starting with a prebuckled shape.

If I had to go the repair route, I would have it straightened, then check for any cracking due to the straightening with mag particle testing. If any is found, grind out and repair with weld. Finally, I would weld on an end plate to the top of the section to reinforce the entire thing and help preclude any buckling issues due to it not being completely straightened.

 

[KootK]

I disagree with KootK's point number one about the force being mainly tension.

Not really I suspect. That was only the case when I was assuming that the damage was only to the female ends. Obviously, it's the reverse at the male end.

My concern is much greater when we're talking about male end damage. That said, your repair strategy certainly sounds prudent to me.

 

[jhnblgr]

These structures are subjected to high fatigue loads, I don’t think the repair should be allowed since there will likely be load concentrations that the naked eye cannot see.

 

[dauwerda]

KootK, I definitely interpreted your meaning wrong on the first read - I thought you meant axial tension, I now understand that you were referring to the hoop stress, and I am right there with you.

Fatigue is certainly a concern, but I personally have never heard of one failing at a lap splice joint due to fatigue. That tends to be much more of an issue at the base plate or at hand holes if they are present.

I think these slip joints all end up with hot spots and load concentrations that take care of themselves through localized yielding and redistribution of the loads.

I agree that the straightening process (as well as the damaging process that already occurred) could definitely result in a more brittle steel due to cold working, which is why I recommended checking for cracks. One could use heat while straightening to help prevent further embrittlement of the steel as well. If so, I believe you want to be in the 1000°F range and care should be taken not to go above 1100°F (heat crayons are a big help here).