Engineering / Structural Engineer question

vonleyser · Jul 28, 2019

I am requesting some help on how strong a 5"x 5" x .125 wall thickness
length of 14 feet used as a column support would be. The load would be applied directly straight down.

How much weight could this support before the square tube would bend ?
or bend and buckle ?

Could the 5" x 5" square tube be filled with something foam/concrete, some other filler to increase it's strength ?

Thanks in advance
Mark

Erich · Jul 28, 2019

How will the bottom of the column be anchored?

Milland · Jul 28, 2019

Not an engineer, but my gut tells me that unless your loads are very controlled in line with the center of the tube you're going to get buckling at moderate loads at that length. Complete filling with a rigid setting material like concrete (ideally a hydraulic grout, or something else that expands rather than shrinks when setting) will help, but not as much as thickening the wall and increasing the size of the tube.

This page: Column Buckling Calculator has a number of stress calculators that you can review for helping to understand loads and limits.

vonleyser · Jul 28, 2019

Erich said:
How will the bottom of the column be anchored?

Bottom of column would be welded in place, load is set on top of column, and secured with welded and bolted brackets brackets There are 3 of the upright columns a distance of 20 feet apart to support two large ridge beams.
This would be for a house in the Houston area, so it does get more complicated as it goes.
List of materials going in are.
1) 5" x 15" x 22 feet long ridge beam (2 pieces each 22 feet) guessing 550 pounds
2) 28 Douglas fir rafters 4" wide ,12" deep, 17' approximately 28 pieces, 14 per side
each rafter is 256 pounds
3) 1-1/4" thick tongue & groove Beetle kill pine/Blue pine 1400 square feet
4) 1/2 plywood over the T&G
5) 5" of polyiso insulation again 1400 square feet
6) Metal standing seam roof, again 1400 square feet, 2500 pounds

I knew my simple question would get complicated, exterior walls will be secured to the columns 8' up from floor.

Steve in SoCal · Jul 28, 2019

Um,

Generally you spec a column with a load factor not to yield. It would be far less that the value you seek.

Steve

Milland · Jul 28, 2019

I think that you need a proper structural or civil engineer for your situation. You've got to factor in wind loads, twisting, and other perturbations that take you out of simple constrained column loads.

This isn't the sort of thing you should be crowd sourcing off a website. Harvey may not be the only hurricane you have to deal with...

vonleyser · Jul 28, 2019

Milland said:
Not an engineer, but my gut tells me that unless your loads are very controlled in line with the center of the tube you're going to get buckling at moderate loads at that length. Complete filling with a rigid setting material like concrete (ideally a hydraulic grout, or something else that expands rather than shrinks when setting) will help, but not as much as thickening the wall and increasing the size of the tube.

This page: Column Buckling Calculator has a number of stress calculators that you can review for helping to understand loads and limits.

Thanks for the link, but I can't / don't know how to fill in all the data, which leaves me helpless. :willy_nilly:

Trying to get this correct before I make a big mistake.

Milland · Jul 28, 2019

vonleyser said:
Thanks for the link, but I can't / don't know how to fill in all the data, which leaves me helpless.

Trying to get this correct before I make a big mistake.

I agree, that's why I posted #6.

vonleyser · Jul 28, 2019

Milland said:
I think that you need a proper structural or civil engineer for your situation. You've got to factor in wind loads, twisting, and other perturbations that take you out of simple constrained column loads.

This isn't the sort of thing you should be crowd sourcing off a website. Harvey may not be the only hurricane you have to deal with...

We have an Engineer that looked at all of our junk laying around and worked backwards to build a platform, if I remember correctly (we are checking our paper work now) our Engineer specked these tubes to be ok, they just look awfully thin to me. instead of cutting them back off the platform at this point I am double checking and if I have to add additional supports this is the time to do it, since they will be hidden in the wall cavities.

Milland · Jul 28, 2019

Gosh, like I said I'm not a real engineer, but even real engineers make mistakes (buildings fall down, rockets go boom (the wrong way)).

I don't mean to be an ass (can't help it though), but if I were you I'd get a second opinion from another engineer. Without seeing plans I wouldn't make any guesses, but you are correct to be worried about structural failure after the fact - it's so much more expensive and disruptive than getting it right the first time.

In your area I'd add in corrosion concerns for steel structures that are hidden, did your current engineer speak to that issue? Do you get salt water air blown in from the coast?

Rob F. · Jul 28, 2019

I do a fair amount of structural columns for buildings out of HSS and they are always 1/4" or thicker for what I am making.
Many times I will add straps to heavy wide flange beams to just sit on 4x6 wood posts.

Milland · Jul 28, 2019

Rob, are you an engineer or are you working from their specifications?

vonleyser · Jul 28, 2019

Milland said:
Gosh, like I said I'm not a real engineer, but even real engineers make mistakes (buildings fall down, rockets go boom (the wrong way)).

I don't mean to be an ass (can't help it though), but if I were you I'd get a second opinion from another engineer. Without seeing plans I wouldn't make any guesses, but you are correct to be worried about structural failure after the fact - it's so much more expensive and disruptive than getting it right the first time.

In your area I'd add in corrosion concerns for steel structures that are hidden, did your current engineer speak to that issue? Do you get salt water air blown in from the coast?

No salt issues here, we are 75 to 100 miles inland.
We have found a product that seems real good on rusted metal, Corroseal, painted on all of the exposed beams that were rusted, turns black, looks good, now the time test.

And I don't mind you being an ass, as I am one also at times.

vonleyser · Jul 28, 2019

Rob F. said:
I do a fair amount of structural columns for buildings out of HSS and they are always 1/4" or thicker for what I am making.
Many times I will add straps to heavy wide flange beams to just sit on 4x6 wood posts.

If these were 1/4' wall I wouldn't be here asking, but theses look unsafe to me, our
Engineer specked 18" piers for this, I had a company drill 20" holes and belled them to 36" on the bottom, I am not afraid to over build this house. My piers went from 4" pipe to 8" fiberglass, filled with concrete & rebar, so we will not have any rusting issues in our lifetime or the next generation that live here.

Milland · Jul 28, 2019

vonleyser said:
If these were 1/4' wall I wouldn't be here asking, but theses look unsafe to me, our
Engineer specked 18" piers for this, I had a company drill 20" holes and belled them to 36" on the bottom, I am not afraid to over build this house. My piers went from 4" pipe to 8" fiberglass, filled with concrete & rebar, so we will not have any rusting issues in our lifetime or the next generation that live here.

Anything stopping you from going to 1/4", apart from cost? If I understand correctly, you'll have some walls for part of the height of the columns, properly tied in they'll help prevent buckling and twist failure. But if they're low strength materials or not coupled to the columns well they may not help much.

Rickyb · Jul 28, 2019

Milland said:
I think that you need a proper structural or civil engineer for your situation. You've got to factor in wind loads, twisting, and other perturbations that take you out of simple constrained column loads.

This isn't the sort of thing you should be crowd sourcing off a website. Harvey may not be the only hurricane you have to deal with...

I agree 100%. I am an engineer and would not touch this project with a "14' pole". A little well intentioned info can end in disaster. An architect should be consulted.

Rob F. · Jul 28, 2019

Milland said:
Rob, are you an engineer or are you working from their specifications?

Fab shop, working off stamped drawings.

That said their is nothing keeping you from going larger than what the engineer called out in this situation. Consider the 1/8 wall tube a minimum requirement. Some things, like earthquake moment frames, need to be exactly as drawn for a certain amount of flex, no more or no less.

My thought would be to use the tube as specced since it has been engineered for your use and you already own it. If you are really worried about it fill it with concrete and and a stick or two of rebar. A "normal" house would just have a 4x4 wood post, how much stronger is the 1/8 wall tube than wood?

JS · Jul 28, 2019

vonleyser · Jul 28, 2019

Milland said:
Anything stopping you from going to 1/4", apart from cost? If I understand correctly, you'll have some walls for part of the height of the columns, properly tied in they'll help prevent buckling and twist failure. But if they're low strength materials or not coupled to the columns well they may not help much.

No nothing stopping me from doing this correctly other then me being 61 and doing 99% of the labor by myself.

Milland · Jul 28, 2019

vonleyser said:
No nothing stopping me from doing this correctly other then me being 61 and doing 99% of the labor by myself.

That's why you have to cultivate some young'uns! Nothing like watching another person do the work while you sip a Pina Colada.

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