Built up/Odd shape area reduction

[EngDM]

Hey all,

Clause 13.3.5 (S16-14) specifies an area reduction when calculating compressive resistance for elements subjected to elastic local buckling, and then refers to the width-to-thickness ratios specified in Table 1. My question is, what is the width-to-thickness ratio for a non-specified shape such as a top joist (hat shape). I'd imagine the top legs would follow the specification for the "legs of angles" but I'm not sure what to consider for the rest of the shape to find an equivalent area Ae to use.

 

[jayrod12]

The other plates would be considered supported on each side would they not?

To be honest however, I've always just treated these as per the outstanding angle legs because the limiting factor is really the top plates.

 

[EngDM]

Yea for those shapes that is what I've been doing, but for say a built up shape what would you consider. Is there a link between any of the properties of the shape to the width-to-thickness that can be used to determine this, perhaps a high warping constant or something (just spitballing).