Combined 2-Cross Section Column Equivalent Effective Length Factor

[chrislaope]

I know this topic had been discussed before in this forum by others, but I can not find the original discussed post, so I would rather post my question again.

Please see attached pdf file assuming all ends are pined ends, basically I am trying to find if there is a quick approximate method to estimate the Equivalent Effective Length Factor.

for example, in diagram (B), can I consider this way: top 10' W12x72 column will have a buckling curve along x-axis(top column's weak axis), however bottom 10' W12x72 column will have a buckling curve along y-axis(bottom column's weak axis), so the final buckling curve of the combiined column will along 45 degree between x-axis and y-axis, therefore I can take k=0.707, and get:
kL/ry = 0.707x240"/3.04 = 55.8.

Do you guys think above reasoning is valid or not?

Thanks

 

[structSU10]

AISC design guide 7 has a method to calculate effective lengths for stepped columns (Appendix B). You should be able to use that and be fairly accurate with not too much leg work. They have a chart so it should be quick.