Lifting a 30m 35te Spud Leg: Crane Weight Calculation

[Gixer1127]

TL;DR Summary

Lifting a 30 metre spud leg on the back of a barge with a quayside mobile crane

Hey folks.
A quick question. Not homework, very much work related. I've been asked to plan a lifting operation to lift a 30 metre long by 35te (metric tonne) spud leg from horizontal to vertical. The spud leg is essentially a cylinder approximately 2 meters in diameter. It is held at one end on a pivot pin. As the crane lifts from horizontal to vertical the one end will be pivoting on this pin until vertical when the leg will be clamped into position.

My question is, from initial lift of one end, how much weight can I expect the crane to be lifting? Will it be half the weight and decreasing as the load moves through 90deg until fully supported on the pivot pin?

If it's expected that the load will be 17.5te then I can get away with using our 230te crane providing I can get within 19m of the pick up point. If it's going to be more than 50% of the load weight then I will need to use our 450 crane.

Even better if someone can give me an equation to use in the future for this type of work.
Cheers, Gixer

 

[berkeman]

Can you post a drawing of the setup? Also, who needs to sign off on this at work (for worker liability issues)? Here in the US it would likely be the local Union and EH&S...

https://ehs.berkeley.edu/

 

[berkeman]

Also, is the crane going to be on the barge with the spud legs as it lifts them, or will it be alongside the barge on the dock?

https://www.hmsbroker.com/charter-type/spud-leg-barge/

 

[Gixer1127]

Hi Berkeman. No issues with liability as this will be down to me as final signatory on the plan. Basically, the lifting foreman will draft the plan and I'll review, recommend any changes if needed , and sign off. I'm in Senegal so slightly different rules apply.
That all being said, I just need confirmation of what I'm.thinking. 50% of load weight decreasing as the load swings up through to vertical.

 

[Gixer1127]

Also, is the crane going to be on the barge with the spud legs as it lifts them, or will it be alongside the barge on the dock?

View attachment 338142
https://www.hmsbroker.com/charter-type/spud-leg-barge/

Quayside for the mobile crane and I'll expect the crane to keep tension on the load as it moves to vertical to prevent any shock loading.

 

[Baluncore]

TL;DR Summary: Lifting a 30 metre spud leg on the back of a barge with a quayside mobile crane

As the crane lifts from horizontal to vertical the one end will be pivoting on this pin until vertical when the leg will be clamped into position.

1. Firstly, the side-forces will get you every time. If the bottom pivot is fixed, how will you make sure that the crane lifting wire remains vertical?

2. Just when you think the lift is done, and you breathe a sigh of relief, the vertical force will get you.
As the leg approaches vertical, the vertical force needed to reach that final point in the lift, will equal the total weight of the leg, but since, the leg is attached at the bottom to the barge, the lift force will become equal to the weight of the leg and the barge.

3. Once vertical, any reduction in water level, due to waves, or tide, will present a pseudo-infinite vertical force on the lifting wire, since the bottom pin is then also lifting the barge. The same will happen if the barge moves sideways due to a wind. The down-force on the closest crane stabiliser will punch a hole in the quay, and the lift radius will increase as the crane operator becomes a passenger, on his last day at work.

What started out as an easy lift of half the weight, rising to the full weight as the leg approaches vertical, plus the barge, suddenly becomes another crane disaster video on YouTube.

 

[Baluncore]

The top of a leg, standing on a pivot point as it approaches vertical, will need to be pulled sideways with a small static force, for the leg to become closer to vertical. At that point, the leg will fall over the centre, presenting a significantly greater dynamic side-load and vertical-load, to the crane. The horizontal and vertical mix of that dynamic impulse is dependent on the length and angle of the lifting wire. Once the leg reaches near vertical, the direction of the subsequent fall becomes dynamically chaotic, and quite unpredictable.

A constraint must be set on the maximum leg angle while being lifted by the crane, at say 60° in light winds, or 75° in still conditions. The leg must then be supported by three or more guy wires, before the guy wire lengths are adjusted to pull the leg into the true vertical.

 

[Gixer1127]

Folks, thank you for your replies. Very much the road I was travelling. The dynamic amplification of a lift like this using a crane that does not have motion compensation would be very difficult and potentially dangerous. I will use the points you have brought up to question the team that are requiring this to go ahead.
Thanks again, very good points raised.

 

[Juanda]

Could you share a video of the operation when the time comes?