Percentage Loading in Lift Padeyes

[hungrydinosaur]

Hi Folks,

I am doing a hand calculation to find the percentage loading in 4 lift padeyes on a structure which is 2000mm L x 1500mm W x 1200mm H. Attached image shows a structure with the COG exactly in the center. This would then have a percentage load on each liftpoints/padeye as 0.25 (which is 25%, as there are 4 padeyes A, B, C, D). My question is if the COG is offset from the center by 150mm and 50mm in the horizontal plane, towards one liftpoint/padeye (for example say toward liftpoint/padeye A), how can we calculate the percentage loading on each lift point? Thanks in advance.

Hungry Dinosaur

 

[kingnero]

Perhaps a stupid question, but as this is for offshore, shouldn't you use 200% (or more) of the entire weight, per padeye?

To answer your question see attachment. Basic statics I'd say.

 

[Ussuri]

You have 4 unknowns in the sling load in each leg. You can set up a system of equations, sum in x direction = 0, sum in Y direction = 0 and sum in z direction = 0. The fourth equation is the skew effect, but in answer to your question, sum of vertical loads in one pair of diagonal slings - 50% total lift weight (ie a skew factor of 1.0). You can then solve for your sling forces and then compare the %'age difference in each leg due to your offset.

 

[Compositepro]

Without using load eveners (pulleys or levers) on the support cables you can easily have 100 percent of the load on only two cables. If you rig 4 cables of equal length as shown in the OP. The load will tilt when lifted so the cg is under the hook, and one cable will have zero tension. The problem is indeterminate without some extra rigging.

 

[elreedyman]

i hope to return to dnv for lifting specific for padeyes design or with examples in [URL unfurl="true"]https://www.elsevier.com/books/marine-structural-design-calculations/el-reedy/978-0-08-099987-6[/url]

 

[Clumpweight]

Rather concerned that you are distributing 25% load on each when requirements for the design of a 4 leg sling, in accordance with EN 13414-1 : 2008, Steel wire rope slings - Safety - Part 1: Slings for general lifting service. This code is recognised as complying with the EEC Machinery Directive. This method is intended to be used for a equal leg length sling, but can be used for unequal leg length slings. see attachment.