Crane Tipping Factor of Safety

[EricaB]

I'm working on modifying an existing overhead crane. This crane is not a traditional design, it is a derrick style crane. In looking at the seismic analysis, the original design loads were quite low. We are going to try to qualify this crane for the higher seismic loading criteria, and I'm starting to wonder, what is the standard factor of safety against tipping for crane design? Any pointers would be greatly appreciated.

Also, I talked to the original vendor, they suggest a 5 to 1, I think that is a little high, but share your thoughts please.

 

[csd72]

I agree that 5 to one sounds excessive as this level of factor allows for fatigue and abuse of the components which is not really a factor in overturning.

Not sure what it should be though.

 

[Ron]

For mobile cranes, the actual load must be less than 75% of the tipping load. I would probably go to 50%.

 

[EricaB]

This is not a mobile crane, it is considered permanently installed inside of a building. The design criteria is such that if the crane were to experience a lifted load during a seismic event, it would safety retain the load, no tipping allowed.

I've always known 1.5 to 1 for tipping factors, but I can't find anywhere that advices using the higher FOS of 5 to 1.

 

[ToadJones]

Nuke plants and government may have much more strict requirements for overturning/tipping.
I seem to recall 5 to 1 being the correct FOS.

 

[ToadJones]

...i will post reference if I can find.

 

[EricaB]

Nuclear loves to over design.. job security!

I will say this much, the crane I'm asking about is our fuel handling crane, so I wouldn't be surprised if I have to go with the FOS of 5 to 1...

One thing I have found, but it doesn't directly apply to cranes, is in an NRC publication that says 1.5 to 1 for foundation designs, can be reduced to 1.1 to 1 for overturning. However, I don't want to misuse the guidance for foundations to apply to a crane trolley.

 

[ToadJones]

what type of crane is this?

 

[EricaB]

A picture is worth a thousand words...

 

[ToadJones]

handling spent fuel....5 to 1 sounds more than reasonable.

 

[MiketheEngineer]

Just don't stand under it - whatever FOS you pick..

 

[azcats]

I'm not that conservative compared to many of the engineers here. And while the probability of a seismic event during infrequent refueling is probably very low, even I don't think 5 to 1 seems unreasonable for the application.

 

[EricaB]

Probability of a seismic event in Florida.. very small.

However, nuclear requires seismic design, so we design for it.

And it would be impossible to stand under this crane unless you were swimming in the pool, which I would not advise under any scenario.

 

[EricaB]

I found this from ASME NUM-1, Nuclear Crane Code

Interfacing structures and foundations shall be designed such that the maximum resisting moment against overturning (based upon dead load plus rated load) will provide a safety factor of 2.

This seems fairly reasonable, not too low from a risk perspective, largely from the possibility of the loading combintation to ever be experienced by the crane being close to zero.

 

[csd72]

But the pool looks so blue and inviting! and I bet its warm.

 

[EricaB]

About 100º F.. on average for the pool water, about 10ºF less in the building ambient air.. 100% humidity. Great working environment!!