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Load Factor For Mobile Crane.

Load Factor For Mobile Crane.

Load Factor For Mobile Crane.

My friends

I have to check a concrete framed building and slab for the case of a heavy crane that will support it temporarily as a steel superstructure is erected. What load factors would be appropriate for use with ACI?

1.4 DL + 1.4 Crane Weight?
1.2 DL + 1.6 Crane Weight?
1.2 DL + 1.2 Crane Weight?

The last one makes sense to me since crane weight is a well determined dead load and 1.4 would be conservative for such a short term loading(about a week at the same location). The ASCE publication on construction loads is not specific on load combinations. Is it?

thanks in advance

RE: Load Factor For Mobile Crane.

1.2D + 1.6 * (1.33 x Crane) + 1.6 * Construction Load

Dead weight is permanent and static. Per code, it only includes building materials and permanent equipment. I would also add a dynamic factor on the crane and construction area load.

RE: Load Factor For Mobile Crane.

The crane weight is well determined. The load per wheel or outrigger is not so well determined, and will depend on wind load, among other things.
Soil failure example here: https://www.youtube.com/watch?v=xz71eVreMDc

RE: Load Factor For Mobile Crane.

You won't find explicit code guidance for this.

For mobile cranes on bridges (note, AASHTO is generally more aggressive than ASCE/ACI) I would tend to use 1.25DL and 1.35LL. Depending on operating conditions, I usually also factor the crane and/or the pick weight with a dynamic load factor.

Jstephen is right -- you also want to be careful about the assumptions (or provided values) for crane reactions to the structure. What I mention above was using a pretty refined breakdown of how cranes transmitted load to the bridge in a variety of circumstances (based on lots of experience).

Remember -- considering the duration of load to reduce load factors only makes sense for probabilistic loads like wind or seismic events (excluding timber structures). A load is a load (and a crane is a crane) no matter how long it sits there -- you don't want to race against a failure mechanism.

The name is a long story -- just call me Lo.

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