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In article . com,
says...
Here it is EXACTLY as given in the reference:

Compression = 12000 / (Ld / A) with a maximum of 0.6 Yp

I should have added that: L = length of unbraced span in inches
A = area of compression
flange in square inches
d = depth (or heigth) of
beam in inches

Just noticed that in this booklet the unit for stress is ksi, ie.
Kilopounds per square inch.

The job I used it on had a 360 in. span, 12" beam, 5" flange width,
average fl. thickness 1/2" (I'm guessing here).

Plugging all this into the formula above gets you: 12000 / {(360 x 12)
/ (5 x 1/2)} = 12000 / 1728 = 6.944 ksi or 6944 psi allowable
compressive stress.

If your bending stress calcs exceed this you need a beam with larger
section modulus, or reduced loading. In a structure you'd add
bracing or stiffening to the compression flange. This of course is not
possible with an under running trolley hoist.

Sorry for the confusion.

Wolfgang

BTW: From the formula above you can see that the strength of the steel
does not affect the allowable compressive stress. This is indeed the
case for column buckling calculations where the column exceeds a
certain "slenderness ratio": ie. tall skinny columns can be made from
A36 (36 ksi Yp) which would buckle at the same load as the same column
made from 100 ksi Yp. steel. Neat stuff, buckling.WFH.

Very useful information, Wolfgang. The formula agrees exactly with the
tabulated data for unbraced beams in the AISC Steel Construction Manual,
at least for a W8x15 section, which I checked beacause it's the
travelling beam in my crane.

In the past I've seen large factors of safety for cranes bandied about
with no explanation. If I understand your first post, in addition to
limiting stress in the compression flange of the beam based on the
formula, the max stress in the beam must not exceed ultimate tensile/5.
UTS for A36 is 58-80 ksi, so 12-16 ksi max stress, compression or
tension, in the beam. Is that your understanding?

Is this a general factor of safety that applies to all components in the
lifting gear?

Ned Simmons