40' I-beam span to be able to hoist 4000lbs in center?
Would need to know what the web height is and what else it's supporting. My opinion is its probably unsafe since it isn't designed for it.
This would require a minimum section modulus of 13.33 in? to avoid exceeding the tensile yield stress of structural steel. S = M/Fsy = 2000*20*12/36000 = 13.33 in?
