Lifting Analysis with Cables and Spreader Beams

I am preparing a lift analysis using cables and 2 spreader beams. I have tried multiple support types and tension members (for the cables) which resulted in unstable conditions. My latest attempt is using "Fixed but" supports and cables with a non linear cable analysis. The structure appears to be stable and the results look like I would expect. In the output, I notice the program is noting zero stiffness (directions 4,5,6) at the supports (crane hook) and ignoring the the moments. I also have an instability at one of the spreader beam attachment points and STAAD added a weak spring. In my model, the lifting points are geometrically centered, but NOT aligned with the center of gravity. I'm assuming the rigging contractor will adjust his lift points according to the COG. STAAD file is attached.

- Since this is my 1st time using this analysis type am I doing it right?

- Is the added spring on the spreader beam connection due to unbalanced loading (not aligned with COG)?

- When the program says "weak spring added" - how strong/weak is it? 


5542 - ChemPro GTE Lift 4.std

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