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M-salem
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Join Date: Mar 2009
Location: Abu Dhabi - UAE
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Boom Stress Calculation for Offshore Crane

12/08/2009 12:04 AM

We have offshore crane that has 5 sections with total length of 115 ft with following dimensions :-

Crane static load is 30 ton

Boom cords dimension is 5" diameter with wall thickness 9.5"

Boom lacing is 3" x 6.35mm

Our concern is that we need to replace the tip & middle section with new ones that have same cord dimension but different lacing dimension of 4" x 8.56mm.

Please advise if this replacement would be acceptable from engineering point of view.

Thanks
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ba/ael
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#1

Re: Boom Stress Calculation for Offshore Crane

12/08/2009 7:30 PM

The chord dimension is 5" diameter with wall thickness of 9.5"? I assume you mean 9.5 mm? Why do you mix Imperial and metric dimensions?

If the only change you are proposing is to replace 76 x 6.35 RHS (Round Hollow Section) with 102 x 8.0 RHS ( can't find 102 x 8.56 RHS) then the new lacing members (assuming the same yield strength) will be stronger than the old ones. They will also be heavier, thereby affecting the magnitude of the lifted load.

You should retain an engineer familiar with this type of design to review your proposal and advise how best to proceed. It is foolhardy to act upon engineering advice from a forum such as this.

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Kev_brown
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#2
In reply to #1

Re: Boom Stress Calculation for Offshore Crane

12/09/2009 9:27 AM

Just as an off-topic comment.

A few years ago I was having a carpet fitted and the person who came to measure up started stroking his chin and sucking his teeth and came out with the statement that I was going to struggle to get value for money as rolls of carpet come in either 4m or 5m widths but the width of my room was 4m and 2inches!

I just looked a little shocked!
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M-salem
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#7
In reply to #1

Re: Boom Stress Calculation for Offshore Crane

12/17/2009 1:06 PM

Thanks Bruce for your comments, actually, we have done the engineering study on the stress and the weight through our engineering department, and got the approval from the manufacturer, however, this approval was not documented as it should be, and I wanted to lessen to other opinions.

Study showed that no big difference in total weight, and new lacing can stand the stress that will be applied

Could you advise any software that can do CRIMONA calculations?

Regards.

Salem
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atsysusa
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Join Date: Nov 2009
Location: Washington DC area
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#8
In reply to #7

Re: Boom Stress Calculation for Offshore Crane

12/17/2009 2:22 PM

Don't you mean CREMONA Analysis? But now you have lost me again. If you are still referring to validating the design don't you want to do Finite Element Analysis?

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atsysusa
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#3

Re: Boom Stress Calculation for Offshore Crane

12/09/2009 9:47 AM

Recipe for disaster. Pay attention to Bruce's advice and retain a licensed mechanical engineer who specializes in cranes and hoisting equipment. The absolute worst thing you can do with a boom crane is mix + match - unless you want to make a U-tube Movie of people dying.

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CaptMoosie
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#4

Re: Boom Stress Calculation for Offshore Crane

12/09/2009 10:55 AM

Hello,

Contact the original designer/manufacturer of the crane for an engineering review. Hope they they have a Licensed Structural/Mechanical Engineer on staff to review any proposed rehab of your crane. If they're any good they'll investigate metal fatigue as well.

.....the previous responders to your posting are absolutely correct about retaining the services of a licensed professional engineer WHO IS QUALIFIED. DO NOT TAKE ANY OTHER ADVICE FROM ANY FORUM AS IT WILL BE A RECIPE FOR DIASATER!!!

Just curious as to why you want to make these structural changes?????

Have a great sunny day!

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pipeit
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#5

Re: Boom Stress Calculation for Offshore Crane

12/09/2009 4:45 PM

Exactly! When I read the OP my head was going side to side with the responses and good answers it is now going up and down, I don't like those kind of You Tube videos anyway.

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atsysusa
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#6
In reply to #5

Re: Boom Stress Calculation for Offshore Crane

12/09/2009 5:46 PM

If you like the answer - rate it {:>)

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