1. An electric hoist, in which the load is supported on two lines, is fitted with a -inch improved plow steel (IPS) wire rope that wraps on an 8-inch-diameter drum and carries an 8-inch sheave with an attached hook for load lifting. The hoist is rated at 1500-lb capacity.
a. If full-rated load were lifted each time, about how many “lifts” would you predict could safely be made with this hoist? Use a fatigue safety factor of 1.25. Note that there are 2 “bends” of the rope for each lift of the load.
b. If the hoist were used in such a way that one-half the time it is lifting full-rated load but the rest of the time it lifts only one-third of rated load, what hypothesis or theory would you utilize for estimating the number of lifts that could safely be made under these circumstances?
c. Numerically estimate the number of lifts that could be safely made under the mixed loading described in (b). Again, use a fatigue safety factor of 1.25 in your estimating procedure.
