huangyhg

cruciform column consisting from "i" shaped profiles
i have a problem with the design of cruciform column consisting from "i" shaped profiles. should i consider the them as two parts and consider only the part which is in the bending direction or add the weak axis strength of the other part?? i don't know exactly which part of the code (lrfd)i should use..(f1 to f12)
and also i wonder the axial load design...if there any writings or source for an example calculation, i'd appreciate much..thanks for your help..
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i did the same recently. i guess you mean an i section with it's flange against the web of another i section. i would consider it as a built up section and work out the moment of inertia and the elastic modulus of the combined section. i don't know anything about us codes but to be safe i would design it using only the elastic modulus as it is not a very compact section any more. then you have to ensure that they are connected enough to allow sharing of forces evenly.
carl bauer
i agree mostly with carlbauer. that assumes the sections are welded together. you might have to consider slenderness of the various elements to guard agains local buckling.
if you are actually building this from rolled "w" shapes, then you don't need to worry about slenderness.
see section e4 (b) (i) of aisc 13th ed.
cruciform shapes also bring up the limit state of flexural-torsional buckling, where they twist on their own axis.
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