1

I currently have an aluminium (aluminum?) pole that's about 1"1/8 across, and it's embedded into concrete. I need this pole taller, and can acquire exactly the same spec pipe in any length to do this.

The pipe doesn't need to be directly end-to-end (there's nothing flowing through), but it should keep its position very well. There will be a slight load (~1kg) on this additional section, but not much. I cannot weld this pipe, but I can drill it or otherwise modify it.

What's my best option here? I've had three so far, and I'm not sure any are what I'm after.

  1. Drill and attach side 'plates' with bolts through.
  2. Find a pipe as near to the internal diameter as possible, and drill through the outer and inner pipes with bolts.
  3. Stagger the pipes, drilling and applying bolts the whole width.

Here are some quick visualisations of these:

Pipe visualisations

Are there options I'm missing to do this, perhaps?

For reference, the pipe is similar to this:

Aluminium pipe image

  • Am I reading this correctly? Isn’t 1kg about 2 lbs.? – Lee Sam Jul 15 '18 at 21:19
  • @LeeSam Yessir! – Dan Jul 16 '18 at 15:39
3

This gets close to opinion, but I'd lean toward the internal sleeve. It can be extra long without being unsightly, which will give a bit more strength.

The external plates would probably be fine.

Unless you could overlap option 3 quite a bit (>12" is what my intuition specifies), it doesn't strike me as being as strong.

  • An external collar might be stronger. If there is very little load, though, and appearance is important, I'd use an internal pipe held with construction cement (e.g. Liquid Nails). By filling voids between the pipes, this makes for a stronger joint, where there is less stress concentrated into a small area. Drilling holes in the pipe weakens it at that point. – DrMoishe Pippik Jul 15 '18 at 20:59
  • I would agree with internal sleeve and use a set screw on each side of the joint to hold it in place if a tight slip fit, other than that I might try to thread each pipe and screw them together with a coupling but a 1-1/2. Threading dies are expensive (do you have any electrician or plumber friends? ) my die set for a hand threader goes up to 2" but some only go to 1-1/4 as larger gets tough. – Ed Beal Jul 15 '18 at 21:25
  • Sounds like most might prefer an internal pipe if possible. That'd certainly be neater, though I now need to see if I can source a pipe exactly the internal diameter needed... – Dan Jul 16 '18 at 15:41
  • A hybrid of 1 and 2 might help to prevent the nuts against the aluminum from yielding the aluminum over time. Aluminum has no fatigue life, so any rocking motion will eventually cause it to embrittle around the nuts, so having a steel inner and outer brace would help significantly. – Hari Ganti Jul 16 '18 at 21:23
0

So when we examine materials for structural support, we look at vertical loads and horizontal (lateral) loading.

For VERTICAL loading, the end-to-end connection with either an interior or exterior connector is far superior to the bolted connection in “single” shear. Depending on what the length of the pipe is, it a 1 1/8” steel pipe will support about 3 kips up to about 5’ long. The single shear connection is significantly less, depending on size of bolts, grade of steel, etc.

For HORIZONTAL loading, it’s based on length of pipe, grade of steel, size of bolts, amount of overlap on piping, etc., but the single shear connection is still significantly less.

For 2 lbs. of loading, whichever is easiest and be a snug fit will work.

BTW, connecting a round pipe to a round pipe in single shear could be difficult...from a practical stand point.

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