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StructuralEng, Consultant
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Experience:  Structural Engineer
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From Canada. We're hoping to build two mezzanines the length

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Good evening from Canada. We're hoping to build two mezzanines the length of a 78'x42'x18' shop, 10' high) One row of support posts (into a 6" concrete base) would ideally span 25', giving us space to unload 24' lengths of fabrication steel into racks. So subtract some space for stairs at the door end, and we get four posts at ~25' spans. The mezzanine we hope will house shelving and racks (fasteners and hardware, only things we'd carry up the stairs), and atop the I-beam that will span the 25' we hope to run a rolling A-frame, from one mezzanine to the next spanning ~18'.
For my peace of mind, could the human answering this name the prime number that lies between twentysix and thirty?
What material would be ideal for the heavy support posts (I-beam, square tube, round?)
What material would be ideal for the "light" support posts along the wall (we estimated seven posts, but because it's along the wall, it's easy to double the number)?
What material would be ideal for the span of 25' (we have access to lots of 6x15lb I-beam, but I'm fairly sure that would be undersized)?
The rolling A-frame would be rated for 2-ton. The floor joists we think would be 2"x8", at 16".
I can help
That's a pretty slick test :-)
Customer: replied 9 months ago.
Thanks :) it's helpful to carry a large bag of scepticism when roaming the internet.
Customer: replied 9 months ago.
Will have to forgo the phone, twin babies are sleeping... yay small business.
Do you have a sketch of what you're trying to describe?
Customer: replied 9 months ago.
Ehhhh, sort of. Imgur link OK?
Customer: replied 9 months ago.
Customer: replied 9 months ago.
Brb in 5. Putting third child to bed.
Customer: replied 9 months ago.
Customer: replied 9 months ago.
No problem with the link? I can send the file through the justanswer system if you like.
Can you attach with the paper clip icon?
Customer: replied 9 months ago.
How's it going?

Are you able to attach your file with the paper clip icon?

Customer: replied 9 months ago.
I did yesterday with the "Add files" button.

Hmmm... I don't see it here.

Could you try one more time?

Customer: replied 9 months ago.
Will do, just a sec. If you scroll up I sent a link to the picture on imgur, you can try that too.
Customer: replied 9 months ago.
How goes?

This steel beam size is to span the 25' supporting 12' long joists and a 125 psf LL for a light storage in a warehouse.

You can plan for a W16x45 beam ASTM A992 Gr. 50, but the joists will need to be detailed to brace the beam against lateral torsional buckling.

Customer: replied 9 months ago.
Beautiful, and the support posts?

Assuming the system is braced laterally with rods or something similar, you can plan for 5x5x3/16 tubes. This assumes axial load and not eccentric connections.

Customer: replied 9 months ago.
Great! That pretty much covers it. One last question, the wall-side of the mezzanine that will have 12' spans, how much smaller i-beam can we get away with?

W8x18 with the same bracing requirements against lateral torsional buckling.

StructuralEng and other Structural Engineering Specialists are ready to help you
Customer: replied 9 months ago.
You've been a great help, thank you.

No problem. I'm happy to help. Good luck with your project.

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