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Understanding Structural Systems and Seismic Impact of Design [Exercise B]
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Hello, can I get a more detailed explanation of how to solve question 9: “Within the program, the client specifies a 80’x50’ rectangular assembly space with movable chairs. The footing on the perimeter of the foundation wall is designed to be 1’ wide within silty clay. Which of the following statements are accurate?”
I understand how to get the vertical foundation pressure from IBC Table 1806.2, but not sure the logic behind how to calculate footing size required to support live load.
Thank you in advance!
@sedona.quimby Thanks for your question! In this calculation, you’re converting the total load the soil has to carry into the minimum footing bearing area needed so the soil pressure doesn’t exceed its allowable bearing capacity.
Per IBC Table 1806.2, silty clay can support a vertical foundation pressure of 1,500 psf. Using the basic bearing relationship: required area = total load / allowable soil pressure = 400,000 lb / 1,500 psf = 266.7 sf → round to 267 sf.
Now compare that to the provided footing area to determine if the foundation is sufficient. A 1 foot wide continuous footing around an 80’ x 50’ rectangle has plan area = perimeter × width = [2 x (80 + 50)] x 1 = 260 sf.
Since 260 sf < 267 sf, the footing as designed is not sufficient for a 400,000 lb load at 1,500 psf. You’d need slightly more width or another load path.
Hope this helps!
Kiara Galicinao, AIA, NCARB
Product Coordinator
Black Spectacles
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Can you please help me to understand the logic behind the formulas used in question #1 & 2, about the ‘Beam Overhanging One Support - Uniformly Distributed Load’?
Got it, thanks for the explanation!