50 year old gantry crane rail maintenance 1

[MrJB]

Hi all, We have been approached to provide structural engineering advice/maintenance measures for the ongoing operation of a number of 50 year old overhead gantry crane rails enclosed in an even older shed. There are two rails. One was originally rated to about 30t and the other 10t. The rails are about 150 and 80 metres long respectively. Design life was probably 25 years although the cranes have been relatively lighlty used ie lifting to near max capacity may 200 times/year and even less so in the last 10 years. They were downrated a number of years ago to approx half their original capacity due to fatigue related concerns by another firm.

There are 3 solutions that we are considering:
1-Condition analysis and further downrating of gantry cranes with a limited lifespan
2-Condition analysis and strengthening of existing rails/columns ie propping the crane rails mid span
3-Replacement of crane rails although stability of the rails would probably still come from the old shed.

Project cost, lifetime cost and down time for carrying out repairs/upgrades are factors. We would like to propose the most time/cost effective solution that can be justified from an engineering point of view.

Does anyone have any recommendations/experience in a similar situation and/or experience analysing crane girders for fatigue?

Thanks

 

[SlideRuleEra]

...the cranes have been relatively lighlty used ie lifting to near max capacity may 200 times/year and even less so in the last 10 years.

They were downrated a number of years ago to approx half their original capacity due to fatigue related concerns by another firm.

There are 3 solutions that we are considering:
1-Condition analysis and further downrating...
2-Condition analysis and strengthening of existing rails/columns...
3-Replacement of crane rails...

We would like to propose the most time/cost effective solution that can be justified from an engineering point of view.

Does anyone have any recommendations/experience in a similar situation...

As a "sophisticated" Owner, I question the other firms downrating, unless supporting engineering backup is available to justify that decision.
If backup exists, suggest your firm review it as part of the current condition analysis.

I also question your firm's approach to the problem. The proposed three solutions dictate that "something" be done... further downrating, strengthening, or replacement. Also, your firm's "time/cost effective solution" will almost certainly be further downrating (zero cost and zero repair/replacement time required).

Suggest your firm propose a thorough condition assessment, including with the cranes loaded. Then there could be five (5) solutions that "can be justified from an engineering point of view":

The three your firm is currently proposing plus
4) Previous firm's downrating remains unchanged.
5) Upgrade capacity, but not necessarily to original value.

 

[dik]

Can you reliably test the existing setup for fatigue failure or impending failure? What current loading do they require for their hoists? Why did the other firm downgrade the capacity? Was it based on anything... or did they just think it was the thing to do.

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-Dik

 

[EdStainless]

When we looked at our cranes, we had both a structural and a crane expert involved.
Our footings and columns were fine.
We replaced crane wheels and rails, along with reinforcing the rail supports.
We ended up using heavier rail that the original. Design rules have changed over time.
We knew the condition of the bridges and hoists so those were not an issue.
We did the work in sections to minimize disruption.
And we were able to preserve the original ratings.



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[IRstuff]

4) Previous firm's downrating remains unchanged.

I would see this as a corner point of option 1, since "condition analysis" could suggest that no change is needed.

the cranes have been relatively lighlty used ie lifting to near max capacity may 200 times/year and even less so in the last 10 years.

Unless you review actual video footage of every operation of the crane, I would take this would a grain of salt.

We delivered an instrument once to the Navy and when installed, they complained that the instrument was misaligned, but we argued that it was in alignment when shipped. We asked, "was it dropped?" and they responded, "Of course, not." We get the instrument back, and the mounting flange that was 2" thick aluminum had a corner bent upward by a solid half-inch, so obviously dropped, and on a corner. As with detective mysteries, "everyone lies," so trust but verify. And in this case verification is not possible.



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[XR250]

Seems like there has to be more sophisticated processes for determining fatigue? Aren't there any x-ray methods? Otherwise, how do you do it?

 

[EdStainless]

We did UT of the rails and actually removed a couple of rail supports for PT and UT examination.

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P.E. Metallurgy, consulting work welcomed

 

[human909]

A quick google results in lots of NDT companies specifically mentioning gantry cranes in my area. Surely there would be other NDT experts in your area.

I'd start with a blank slate and ignore the previous down rating unless it was based on some solid investigation. Just because it has a design life of 25 years doesn't mean it won't last 250 years.

I'm hardly an expert on fatigue but I suspect that fatigue of major members would be fairly negligible. Fatigue for steel is normally in hundreds of thousands or millions of cycles. Unless this crane is in HEAVY industry then it might only be lifting 20T-30T once a month or once a year.

I suspect that corrosion (if applicable) and changes in design rules would have more impact than fatigue.

 

[MrJB]

Thanks for the input.

The facility is a precast concrete yard so just by the nature of the buisiness they are limited to one/two heavier lifts (but not necessarily max capacity) per day per precast bed and a number of lighter loads ie reo cages. There isn't a detailed record of the entire lifting history or number of precast beds yet in the last few years the half rated capacity has worked just fine and client would be very content to maintain this until a following review.

We work under Australian Standards. A fatigue assessment is required based on lifting cycles and load spectrum lifted. If they lift max capacity 10% of the time and less than 50% of capacity the rest of the time the standard allows upto 250 000 lift cycles without requiring fatigue considerations. Give 50 years of operation x 200 work days x 20 lifts per day that comes out at 200 000 lift cycles. They would have another 50 000 lifts up their sleaves below fatigue considerations would be required. If our client provided us with the lifting history of the cranes to the best of their ability and we stated something along the lines of based on X provided by the client we think you should do Y - how far could that go for showing our engineering due diligence? This could help paint part of the picture and the numbers above could be wildly inaccurate.

The condition analysis/assessment is a given as a first step of the entire shed and gantry crane rails. The outcome could be no additional work to the crane rails yet we would need some very good analysis to go against previous engineering judgements. Despite being located on an old swamp the footings/slab appeared to have performed adequately. I doubt our visual assessment would pick up any fatigue based concerns though in the rails. Doing some NDT on a couple of select gantry crane rails is a good idea and potentially expanding if there are any issues detected. Has anyone gone through this process?

Dik - how would you propose reliably test the existing setup for fatigue failure or impending failure?

Edstainless - what is UT and PT?

 

[dik]

I don't specialise in I'm not into testing for fatigue, and would seek out someone that was.

I would think that ultrasonic (UT) and possibly dye penetrant (PT) or mag particle would indicate if there was an initiation of fatigue cracking, but am not confident. There may be other testing that is better, and the ones mentioned may have shortcomings...

There are others on this site that specialise in this type of work and I was hoping that other members might fill in the 'blanks' a bit. I'm still in a learning mode...

A periodic review of the structure may be in order since the loading history may not be fully known... even without a history, a periodic review should be considered.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[human909]

The condition analysis/assessment is a given as a first step of the entire shed and gantry crane rails. The outcome could be no additional work to the crane rails yet we would need some very good analysis to go against previous engineering judgements.

Why don't you find out what those judgments were based on. From your description they were based on nothing at all.

Doing some NDT on a couple of select gantry crane rails is a good idea and potentially expanding if there are any issues detected. Has anyone gone through this process?

Why don't you just ask the local experts.

https://www.walshsteel.com.au/non-destructive-testing/

https://ixt.com.au/