Answer to Quiz No. 3

ERECTION PROCEDURE:

1. Hook up cranes to tower boom at position 1.
2. Hoist the tower boom to position 2.
3. Pin tower boom to mast.
4. Release load on Crane B.
5. Hook up boom pendants.
6. Tighten up on the boom suspension.
7. Unhook Crane A.
8. End of procedure.

From a crane capacity stand point, is this a safe lift? YES or NO



No, this is not a safe lift.

At POSITION 1, crane A has a 13.33 kip load and crane B has a 26.67 kip load. A kip is 1,000 lbs. 100% of capacity chart for crane A is 13.33/.9 = 14.81 kips and crane B is 33.34 kips. At POSITION 2, after the tower is pinned to the mast and the load to crane B is released, the load to crane A increases to 30.00 kips. This is an increase in load of 125%, well out side of the capacity chart and into the accident range.

At POSITION 2, if the load to crane A is released first, the load to crane B increases to 48.00 kips. This is an increase in load of 80%, well out side of the capacity chart and again into the accident range.

Many times, the transfer of a load in the air from one crane to another is a subtle thing and usually happens when using two lift cranes. All lifts should be carefully looked at from a load transfer point of view.

This rigging quiz is the result of a lesson learned experience where the load to crane B was release first and crane A started to turn over. To save the crane, the operator dropped his end of the tower boom and it was severely damaged when the tip hit the ground.


    


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