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Steel Combined Forces (Chapter H)

Steel Combined Forces (Chapter H)

Steel Combined Forces (Chapter H)

(OP)
So I've always wondered this...

In Chapter H, Section H3, Part 2, it has an equation for combined forces (shear, torsion, moment, torsion). But, when Torsion is less than 20%, it says go back to H1, where those equations only have Axial and flexure, but with obvious different mathematical relationships than the latter. I have read the commentary, and I get it more or less, but my question is about the shear term. I am wondering when they say if "torsion" is less than 20%, do they really mean the "torsion and shear" together...otherwise...where does the shear term go if, for example, you have no actual torsion?


RE: Steel Combined Forces (Chapter H)

I think they mean exactly what it says. However, you raise an interesting point. What if torsion were at 19% of capacity and shear were at 82% of capacity? That would be a problem by section H3, but not by H1. That is what you're getting at, right?

Personally, I don't know how you could get shear demand quite so high without having a similar effect on moment demand. Not in a realistic scenario. But, if you could, then this would be a loop hole in the code logic. At least in my opinion. That being said, I think it is mostly an academic argument unless you can present a realistic scenario where this would happen.

Even if you had a very large shear force applied close to a support point, I think the section would fail locally (i.e. J10) at the applied load.

RE: Steel Combined Forces (Chapter H)

I agree with JoshPlum. I don't think they mean "torsion and shear" when they "say shear". When you have significant torsion (over 20%), that torsion translates to high shear stresses within the section. When you add the shear stress due to torsion to the shear stress from flexural bending, shear may control the design.

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