Static equivalent hoist load
Static equivalent hoist load
(OP)
While in a discussion regarding the analysis of some portable skids that will be lifted with a crane (about 8ft X 30ft) the subject of "hoisting loads" was mentioned. While the hoisting should be performed in a "smooth and consistent manner" it seems logical that a "dynamic load" will be induced. Without doing some dynamic calcs based on a HEAP of assumptions relative to the hoisting maneuver is there a "rule of thumb" or code driven (unable to find in ASD manual, IBC, UBC, etc.) static equivalent that the structure can be evaluated to?






RE: Static equivalent hoist load
Having recognized a potential safety issue, you could upsize every part of the system to increase your factor of safety.
RE: Static equivalent hoist load
If you think about it, a 100-tonne crane can exert a much greater "shock" on a 2-tonne load than say a 10-tonne crane.
RE: Static equivalent hoist load
corus
RE: Static equivalent hoist load
RE: Static equivalent hoist load
I regularly engineer skids for a manufacturer of natural gas metering devices. These skids are up to 60 foot long and may contain multiple metering "runs".
I have found that the largest stresses occur during the lifting and setting operations.
For these skids (composed of tube steel for the base frame and various other shapes for pipe and equipment supports) I base the design on the maximum deflection during the lift. Working with the manufacturers engineers we have determined that for our purposes the maximum deflection allowed is 3/8". If the calculation indicates that we exceed that value then we simply add more lifting locations. Since stiffness is more important than stress we very seldom obtain stresses beyond 10 ksi in the base steel.
RE: Static equivalent hoist load
Do you apply a percentage "adder" to the weight of the skid to account for the hoisting? Or do you just design the skid as if it were just hanging by its lift points?
henerythe8th
RE: Static equivalent hoist load
RE: Static equivalent hoist load
Normally, crane load charts don't require you to add acceleration to the weight of the object, if that helps.
RE: Static equivalent hoist load
I just use dead weight (very carefully calculated) for the lift, but I do add in a horizontal component at the lifting points due to the sling geometry.
RE: Static equivalent hoist load
henerythe8th
RE: Static equivalent hoist load
DPA