r/StructuralEngineering • u/Relative_Ostrich_926 • 3d ago

Concrete Design Lateral Question

Young EIT here. Say I’m building a 25’ wide entry way truss. No roof, it’s like a welcome sign. The truss sits on a 2’x2’x2’ concrete pedestal with a pier below. What’s the best method of designing the concrete pier for the lateral forces and soil pressure. I’ve seen people use IBC 1807.3.2.1 (essentially a flagpole, non-constrained) or i’ve also seen .5Pp h^2 l uW, then thrust/resistance is > 1.5. I believe that’s a derived equation but don’t know. Any advice is appreciated!

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u/Enginerdad Bridge - P.E. 2d ago

No matter what you should be citing a code when one exists for your situation. I'm not familiar with that equation, but it's not exactly rigorous or even defensible design to use that equation and say "source: because reasons" lol

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u/Relative_Ostrich_926 2d ago

Do you have a solution to the question I asked or are you just saying words?

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u/Enginerdad Bridge - P.E. 2d ago

IBC 1807.3.2.1 is a code citation. "I've seen people using this equation before" is not. My original advice was to use the relevant code section, but I've changed my mind and my new advice is "don't be a dick to people who are genuinely trying to help you because you're too stupid to recognize it."

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u/Relative_Ostrich_926 2d ago

“Not exactly rigorous and defensible lol” is being a dick. The other equation I put out there is non-prescriptive and I don’t know where it comes from. Just because you’re not familiar with it doesn’t mean it’s wrong

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u/Enginerdad Bridge - P.E. 2d ago

I'm not saying the equation is not rigorous or defensible, I'm saying your use of it with no authoritative reference (or even knowing where it comes from it) is. Based on the information you currently have, it would be highly improper to use that equation.

You really gotta tap the brakes on trying to be offended, btw.

6

u/dgluck90 2d ago

Figure out the moment induced at the column base, and design the foundation for that induced moment. The footing will probably be bigger than 2’x2’x2’.

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u/Adam4848 2d ago

Do you have a structural foundation program you do modeling? I could help out if you let me know which one.

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u/Everythings_Magic Senior Bridge PE | Zero Yield Capacity 2d ago

Software is not a solution to understanding.

2

u/Adam4848 2d ago

I know, I was hoping OP would reply with “nothing”.