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.

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.

 

[MiketheEngineer]

1.5 seems a bit low - but if you are not standing underneath it -- who cares...

 

[EricaB]

ASCE 7-10 extract:

The structure shall be designed to resist overturning
effects caused by the seismic forces determined in
Section 12.14.8.2. The foundations of structures shall
be designed for not less than 75 percent of the
foundation overturning design moment, Mf (kip-ft or
kN-m) at the foundation–soil interface.

This is where I get the 1.5 from.. it applies to seismic foundation design, which in the case of the crane would be the trolley. But I'm thinking it is a reach to apply the different the principles of foundation design to a crane structure.

The idea is to prevent the crane falling into the pool, this is not allowed under any condition.

 

[drawoh]

EricaB,

I asked this question over in the Structural Forum.

thread507-255357

JHG

 

[EricaB]

Thanks!

 

[Duwe6]

1.5 is actually sufficient. On every major lift, the crane operator will check his Load Chart for both tipping and for weight on the boom. Just make sure that you update the Load Chart for the rig.

And train the operators to rapidly land the load during an earthquake.

 

[PersonalProfile]

Assume you have done so, though suggest you consider reviewing local design standards, acts / regs etc.

Regards,
Lyle

 

[IceStationZebra]

I would be surprised if OSHA doesn't require you to get the original vendor's approval or a certified PE to go above the original design rating. And they should be considering the tipping moment. For reference the safety factor on lifting components is something like 3:1 or 4:1 depending on the component.

ISZ