Crane Outrigger loads

[tmschrader]

Hello

Ia anyone here involved with calculating max possible loads on outriggers given the CG of crane and loads? Or know a consultant that does? Not the pressure loads on the soil but the actual rating for each outrigger.

Most of the articles I found assume a very rigid crane and do not account for any flex in the crane body. If using higher strength 100kSI steel the crane body will flex more. As the crane body flexes a high load cause one outrigger to bend and flex. As the one outrigger beam flexes the next outrigger will start to absorb some of the load. For a 100% rigid crane the crane it may start to tip, and the load does not transfer to the next outrigger. When using 100ksi vs std 36KSi steel this effect of transfering the load to the next outrigger is increased by almost 2.5 to 3 times. Think of the crane body as a torsion bar with 4 beams extending out from the two ends. This should help visualize the difference.


This below article partially addresses what I am seeing with the difference between outrigger max rated loads from a fully (or say more) rigid crane and the lighter 100KSI outrigger bed frame that I am seeing. Apparently, the codes do not address this yet. I talked to a steel MFG last week (SSAB) and some crane MFG's are even using 180KSI!! steel in the most outward boom extensions.

Thanks

https://wheco.com/2012/08/is-that-crane-tipping/

 

[GregLocock]

Given that one foot might break through a manhole cover or whatever I can only assume that each is designed to take the full righting load. Since it is man rated lifting gear at least in Australia I'd expect an FoS of 8, which should be sufficient to cover any extra loads due to elastic deformation.

Cheers

Greg Locock


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[dhengr]

Tmschrader:
Of course, you have to take into account the flexure of the entire crane structure, and a higher strength steel will deflect more from a given a load, than a lower strength steel might before it starts to yield. The crane manufacturer should make some comment on the need to do this, when you move back from the outriggers, in their loading charts, so the total CG does not move out of line by too much. When you have a hundred or 150’ of stick hanging out there this makes a difference in the radius of the lifted load, and this has to be taken into account. In terms of total lateral movement of the boom tip, flexure in the outriggers is probably a bigger deal (roll of the whole system) than some deflection further back in the structure. The crane manufacturer is trying to lighten his machine so it will still be road worth, and you have to account for these higher strength steels and their deflections in your stability calcs.

 

[TimSchrader2]

Hello

Thanks
A safety factor of 8! That's alot. This Boom is not rated for people, just concrete. The critera in the states is to have 3 pads on the ground, it should still be stable with three pads. I have the standard. One pad starting to lift. The linked article shows this

Note that as the crane body flexes the load each outrigger takes can be less then it would be if you assume a rigid crane. Even 65% of the Load reactions calculated using the standard rigid body analysis most often found in documents. You apply moments to the rotating base and calculate reaction loads at the rig supports. The article above is the only article I found that starts to address this effect. The FEA shows less max reaction loads cause the FEA accounts for load sharing caused by the Crane body structure deflecting. It does deflect like a torsion bar when the load is over the side.

 

[GregLocock]

In Oz any rigging that may have people underneath it is a factor 8, tested to 4 annually (thereby using most of its fatigue life up but I digress).

Cheers

Greg Locock


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