Flagpoles

[NLEngineer]

I am looking for some information on flagpole design. I am conducting some preliminary research into the correction of a problem with the pin openings on a flagpole. The flagpole is an aluminum, 50', cone tapered, tilt-down (pin connection pivot point with two steel channels for supports imbedded into the concrete foundation) flagpole in an open area close to the coast line that needs to be able to withstand Category 2 hurricane wind speeds and gusts (up to 120 mph). The problem involves the holes on the flagpole itself. A hurricane hit the area in 2003 and since then these openings have been getting larger, the pins are "banging" against the openings and forcing the aluminum to roll back whenever the wind changes. Presently the flagpole is on a tilt and we are looking for some way to rectify the situation without replacing the flagpole. I have come up with a few ideas on how to right the situation, but I am unfamiliar with flagpole design and any input would be greatly appreciated.

Thanks
NLEngineer

 

[pba]

Replace the flag pole.
This one has failed - given the nature of Aluminium in terms of fatigue you cannot, realistically effect a repair.
Does it really have to withstand a hurricane?

 

[NLEngineer]

A hurricane is what cause the damage in the first place so basically it would be good if it was able to withstand high coastal winds at least.
Thanks for your help pba.

 

[Peter]

Weld a thick wall tube into the flagpole for the pin(s) to bear against. You can then also weld a doubler onto the outside of the flagpole to locally reinforce the wall.

 

[NLEngineer]

Thanks for the help Peter. That was close to what I was thinking, just wanted to make sure I was going in the right direction.

 

[STR04]

Poles are designed for service loads (10-yr) with a flag raised and strength design (50-yr) with flags lowered. If the flag was up during a hurrican then I think the user is SOL.

 

[vmirat]

What if you filled the bottom section of the pole with concrete up to where the pivot point is? You would have to install a closure plate to contain the concrete. Not only is this fairly simple (no welding), but it would provide counterbalance as you lower the pole for maintenance.

 

[dbuzz]

Aluminium does not perform well in contact with concrete, unless there is some sort of surface protection.

 

[transmissiontowers]

You should be careful welding on aluminum since the base metal heat affected zone can loose its temper.

http://www.alcotec.com/qanda1.htm

_____________________________________
I have been called "A storehouse of worthless information" many times.

 

[vmirat]

Good Grief! You're absolutely right, dbuzz, the aluminum would have to be coated with either bituminous paint or zinc chromate to keep the concrete from eating it alive. I was so focused on fixing the mechanical problem I forgot about the chemical thing.

 

[NLEngineer]

Thanks for all the info everyone. I wasn't thinking about chemical reactions either.

 

[rb1957]

how about bolting/riveting rather than welding ?

 

[pba]

My original response was to replace the flag pole and I still believe that to be the correct solution, but no one else seems to concur! I assume that the wind forces are likely to have done more damage that simply enlarging a pin hole.

If you are to keep the existing pole can't you just replace the pins with larger ones?

 

[TFL]

what about just rotate the pole 90 degrees and redrill holes for the connection. you can add more/larger fasteners to increase capacity

 

[rb1957]

i think the posts are suggesting that the flagpole can be salvaged.

how about bushing the holes ? or use larger diameter pins ...

how much deformation has there been at the holes ? is the pole still straight (straightish) ?

 

[NLEngineer]

The pole is on a tilt, but not by very much, I guess you could say it is straightish (it also depends on how windy it is). There has not been an extenisve amount of damage (the holes have enlarged about 1/4"), most of it occuring during the hurricane, but high winds are slowly opening up the holes even more. Right now replacement is not an option.

 

[rb1957]

a 1/4" is might lot of deformation ! what dia pins do you have .... 2" ?? how thick is the flagpole (wall) ... ie bearing area for the pins ?

can you lower the flagpole, or do you have to repair in situ (this'll really restrict your options) ? can you access the inside face (near the pins, to rework) ? or the outside face ? i'm thinking of collars to reinforce the damaged area. can you rework the outside face (or is this restricted by the flagpole mounting) ?

how basic is your manufacturing support ... sophisticated (can do machinings), routine (rework stock material), basic (can buy common hardware and materials and beat them into shape) ?

 

[NLEngineer]

I'm not 100% sure on all these questions. I'm new to this job and I am currently unfamiliar with the manufacturing support, but for this project I believe it would be more on the routine side of things.
But I can say that the flagpole can be lowered, and taken off the supports in order for it to be fixed.
We do not have exact information about everything right now, as this is preliminary and we're just looking at ideas at the moment. I believe the wall is about 0.188" thick and the pin diameter is about 2". I think I may be mistaken at the increase in hole size as I am trying to track down original measurements or drawings of some sort, then I'll know more.
There is also space between the pole and it's supports because there possible used to be a sleeve there.
I apolgize for the lack of info, but I myself am having a hard time tracking down certain things at the moment.
Thanks for all the help though!

 

[rb1957]

could someone remake the last 2' to 4' of the flagpole, and then "cut and paste" ? this would move the more complex manufacturing tasks to somewhere where they can do them, but costs money ?

can you "precision" drill holes ... if you had to replicate the existing holes in a solid repair piece ? i'm picturing repair plates around the outside of the flagpole, the inside would be nice too (possibly manufactured off-site); then you'd need to replicate the original holes.

can you freeze fit bushings ? say in LN2. this would be a good way to repair the holes, but can be a little bit tricky ... i've never dealt with 3" repair plugs !?

why is replacement out of the question ?

 

[NLEngineer]

Replacement is out of the question right now, because I work for the governement and by the time someone would get the paper work done to replace it, it will have failed for sure. It's not exactly at the top of the list of things to be done at the moment, and will probably be replaced in after a couple of years anyway (especially if we are unable to come up with a good solution).
Thanks for all your ideas anyway, they've been very helpful.