I am trying to get an idea of how much load / weight (2) 9 foot long piece of 3.5" x 3.5" x 1/4" thick hollow square steel tubing can support when used vertically as a column. The columns would be place at each end of a 17' engineered lumber beam(Glulam) There will be 3.5" x 5.5" x 1/4" flat stock at the top and bottom of the pier which would be welded the tube. The tube would be secured using anchors to a concrete footing at the bottom and secured to the bottom of a glulam using structural fasteners.

Just for the sake of concentrating specifically on the load bearing capacity of the steel columns. The beam is supporting a residential living area with a live load of 40 psf and a dead load of 20 psf.

  • Will the load be centric or eccentric?
    – Solar Mike
    Commented Mar 4, 2022 at 12:09
  • How can I correct you? this is your project so you know the details - all we can do is guess.
    – Solar Mike
    Commented Mar 4, 2022 at 12:25
  • @SolarMike by correcting his understanding of "centric" and "eccentric". I would take those to mean "centric - is the post in the middle of the span" and "eccentric - is the post off-center of the span", but I didn't look them up...
    – FreeMan
    Commented Mar 4, 2022 at 12:32
  • 5
    Bit worried when people ask these sorts of questions tbh. There are fixed and variable loads (rain, snow etc), structural stability unknowns, safety margins you should apply etc etc etc... What does the larger structure look like, and will it involve use by people? If so, I would consider involving a professional.
    – MiG
    Commented Mar 4, 2022 at 12:37
  • 1
    Would be nice to know what it is for. Holding up a beam to hang flower pots is much different than holding up a beam supporting a house. Those posts should hold a few tons straight down without any other types of loads acting on them. Having the beam with a big hot tub above it in the centre is much different than an empty floor.
    – crip659
    Commented Mar 4, 2022 at 13:01

2 Answers 2


According to the Manual of Steel Construction, a 9’ long x 3.5” x 3.5” column with 1/4” side walls can support 47 kips. (47,000 lbs.).

+1 to you for giving all the info needed. Often people forget to include the thickness of the column.

Btw, this is based on A36 steel. Probably the weakest steel you could possibly find.

  • Thank you for your response I have A500 steel columns. I appreciate your feedback.
    – Andrew
    Commented Mar 5, 2022 at 1:59

More weight than you have ; about 100,000 pounds or more depending on the strength/type of steel. Very roughly, 3 square inches of steel with minimum yield strength of 35,000 psi. As the comments point out, the limit will depend on geometric factors such as buckling, etc; not the strength of the steel.

  • Thank you for your feedback blacksmith. It is much appreciated.
    – Andrew
    Commented Mar 4, 2022 at 16:21
  • "Slender column loading" will likely be the limit. But I'm not going to try to calculate it. Short enough columns have to be crushed. Long slender columns bend sideways and buckle. Push on the ends of a hunk of ziti and a hunk of spaghetti to get a feel for the difference ;-)
    – Ecnerwal
    Commented Mar 4, 2022 at 18:10
  • "As the comments point out, the limit will depend on geometric factors such as buckling" - That's the the real answer, and you haven't given it. But your opening can easily be read to say "you're good to go no matter what" which is a terribly irresponsible opening sentence for this situation. Commented Mar 4, 2022 at 21:16

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