Forces applied to secure points

  • Thread starter jingojamie
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  • #1

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Firslty I should explain that I am neither a highly qualified engineer or physicist howver I am hopefull one of you out there might be able to help.

We have an 'A' frame with two legs attached to the deck on pins, the 'A' Frame is moved forward and backwards by two hydrualic rams positioned behind the frame and operating on each leg, the rams are mounted on pedestals behind the leg pivot points, again attached to the deck.

A winch is used to pull a wire through a block, the winch is mounted between the legs of the 'A' frame. The wire goes to the head of the frame and then down into a moon pool where the load is suspended. The head of the frame is positioned perpendicular to the CL of the moonpool with its mounting points behind it.

To calculate the SWL at the head of the frame I would normally look at the lead angle of the wire and the load giving a mutliplying factor of around 1.75t at the head.

My question is, does the load on the mounting points get spread over all 4 (two with the rams and two with the frame pivots)?

My overall intention is to determine the maximum load lift the setup can maintain but I am not sure what effect the 4 point mounts have on the overall load capacity.
 

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  • #2
nvn
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jingojamie: Can you post a dimensioned diagram of the system? Also show the wire "lead" angle, all pulleys, and explain what is 1.75t. The forces on the system are found using statics.
 
  • #3
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We have an 'A' frame with two legs attached to the deck on pins, the 'A' Frame is moved forward and backwards by two hydrualic rams positioned behind the frame and operating on each leg, the rams are mounted on pedestals behind the leg pivot points, again attached to the deck.
I think since this appears to be a real life safety situation, with peoples lives at definite risk, a competent engineer should be consulted.
The calculation is more than just a question of statics, and bending in the A Frame legs, various safety and condition factors need to be applied, not least to the rams.

I would imagine that such a calculation, followed by regular inspections and tests, is mandatory in most States.
 

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