## Fco expression ?

## Fco expression ?

(OP)

Has anyone seen this expression for plastic compression allowable ...

Fco = Fcy*(1+sqrt(Fcy)/1333) "for Al plate", Fco, Fcy in psi ... dates from mid-60s

used as a column allowable ...

attached the calc

Fco = Fcy*(1+sqrt(Fcy)/1333) "for Al plate", Fco, Fcy in psi ... dates from mid-60s

used as a column allowable ...

attached the calc

another day in paradise, or is paradise one day closer ?

## RE: Fco expression ?

"C"should be your first hint that this has gone by the wayside.It looks more like an empirical formula than some kind of exact one.

Is this for working out the transition from elastic to plastic buckling of long columns?

Does the end of the chapter have references to the source of this calc?

STF

## RE: Fco expression ?

## RE: Fco expression ?

The transitional L'/rho value referred to is the transition between long & short columns. If your L'/rho is greater, you have a long column, which is evidently the case the author had, and you can use Euler's formula. Since he had a "long" column the author does not go on to show the short column formula, which would be a linear function of L'/rho containing Fco. The Johnson-Euler formula is another empirical short column formula. It is parabolic and is often used for steels, whereas a linear short column formula is often used for aluminum alloys.

I do not have a copy of MIL-HDBK-5C to confirm this. Newer versions of MIL-HDBK-5 do not seem to have these formulas. Similar (or identical?) equations appear in Bruhn, chapter C4.5 titled "Column formulas for aluminum alloy tubes". He gives different forms of the equations depending on the exact alloy.

## RE: Fco expression ?

Yes, the Bruhn reference is where it is, LPS for you !

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