Sir Dave,
My conclusion is Bending Stress in stress extended report(even in sustained case refers to
Sb = [(iiMi)2 + (ioMo)2]1/2 / Z (bending stress for expansion case)
so CS2 trying to do is multiply Sb by 0.75 becase Ii and Io is 0.75 of ii and io respectively for sustained case.
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