replying to mjacobsen925, Ray Hayes wrote: Your reply is foolish. This appears to be a valid question about using a pipe section to support a hoist - an overhead lifting design that requires calculation. 1.5" black iron pipe is the support beam suggested for available electric garage hoists.
For any who care, stress = M*c/I = M/s. Bending moment = M = WL/2, s = 0.326 in^3 for 1.5" sch 40 pipe. Assume yield strength=30,000 psi. L=60". stress = M/s = W*L/(2*s). If Safety Factor = 2.0 (low for a lifting operation
- F.S> should be 6 for overhead lifting): Yield/F.S = 30000 psi/2.0 = 15000 psi = W*60/(2*0.326); W = 163 lbs. Yield Strength (30,000 psi) is the load where the pipe will bend without springing back to straight. Original request was for a 1" deflection at the center. This is way overloaded - typical beam limit might be L/360 = 0.167". But just for yucks: max deflection = y = W*L^3/(48*E*I); E=29e6, I = 0.310 in^4 (1.5" sch 40 pipe). y/W = 60^3/(48*29e6&*0.310) = 0.0005, or W/y = 2000, or W = 2000*y. So to get a
1.0" deflection on a 60" pipe (if it did not yield) would be W=2000 * 1.0 = 2000 lbs. *
BUT the stress with that 2000# load would be M/s = W*L/(2*s) =
60/(2*.326) = 184,000 psi - 6 times the yield strength (meaning the pipe would bend to failure). *
For reference, limiting deflection to L/360 would allow a load of: W = 2000*y = 2000*
(60/360) = 333 lbs. This corresponds to a F.S. = about 1.0.
Take away - pipe is not as strong as it looks. Don't stand under that hoist, be careful it does not snag on something that lets it go to its full cable tension unless the support beam can handle that weight.