Maybe.
If your duct is circular, then yes you can analyze it with CAESAR II, being aware of the following limitations:
1) CAESAR II uses the "3D beam" element. This is essentially an infinitly thin stick element. Your analysis is subject to the limitations of this element.
2) Most piping codes develop SIFs assuming the D/t ratio of the pipe is less than 100. If you duct exceeds this, your SIFs are outside the scope of the codes.
3) Your results will be global, system results. Don't expect CAESAR II (or any other piping program) to tell you about local buckling, or any other 2nd order effects.
4) As to what code - where is the duct, what does it transport?
If you duct is not circular, you can't use CAESAR II.
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Regards,
Richard Ay - Consultant