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CHS class 4
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JoshPlumSE
Structural
Generally, the easiest thing to do is this:
1) Determine what b/t ratio will be sufficent to get you down to a class 3 section.
2) Artificially reduce your "b" values to the point where the b/t ratios meet the class 3 restrictions.
3) Calculate some effective section properties (A, I, S, Z, J) based on the reduced widths.
4) Use the reduced properties in your capacity calculations.
There are other ways to do it. The cold formed steel codes have much more complex methods for calculating effective section properties and dealing with local buckling. But, the other method is so much simpler that it just makes more sense to use on anything that can be considered a "borderline" class four shape. If you're way out into the slender range, then the simple method probably isn't as effective.
1) Determine what b/t ratio will be sufficent to get you down to a class 3 section.
2) Artificially reduce your "b" values to the point where the b/t ratios meet the class 3 restrictions.
3) Calculate some effective section properties (A, I, S, Z, J) based on the reduced widths.
4) Use the reduced properties in your capacity calculations.
There are other ways to do it. The cold formed steel codes have much more complex methods for calculating effective section properties and dealing with local buckling. But, the other method is so much simpler that it just makes more sense to use on anything that can be considered a "borderline" class four shape. If you're way out into the slender range, then the simple method probably isn't as effective.
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