Sizing spread footings for overhead warehouse crane

[Zrebse]

I am trying to size spread footings for an overhead 15-ton crane inside a warehouse building. I have an allowable bearing capacity based on the geotech investigation. I have live loads (vertical load on the order of 40 kips with around a 40 kip-ft moment) and the following statement from the structural engineer: "All the loads should be considered live load due to their moving nature. The dead load of the columns and beams is insignificant relative to the magnitude of the crane bridge, hoist, and rated capacity loads." I interpret this statement as meaning that the significant dead loads are just from the weight of the crane and its rated capacity load (shouldn't the capacity load be a live load?).

I am used to sizing footings based dead loads. However, in this case, with such large live loads, it seems that I need to account for the live loads as well. What load should I use to size the footings? Does anyone have a technical or building code reference that would provide guidance for this design? Any help would be greatly appreciated.

 

[PEinc]

Zrebse, you appear to be in over your head. Footings should not be designed for only the dead load. The rated crane capacity is a live load. You should hire a structural engineer.

http://www.PeirceEngineering.com

 

[oldestguy]

Sounds to me like your geotech may be basing his recommendation on something with the soil below. Perhaps you should say something here as to what the borings show generally. Otherwise the recommendation sounds like the geotech is very inexperienced.

I'd get another opinion.

 

[hokie66]

Does it really matter whether you consider the entire load as dead or live? Just take it all as live load, which may be a bit conservative, but that is good for crane supporting structures.

 

[shobroco]

I'm with hokie; all live load simply adds a bit of safety factor. Obviously you don't ignore any of the loading.

 

[chicopee]

All the loads you need to consider + a certain percentage for the crane load test.

 

[TXStructural]

In some soils, I have seen geotechs consider soil capacity to be higher for transient loads (due to settling, compression, or whatever, that occur under constant loads), hence the sizing of footings for dead loads. But obviously the footing design has to consider all loads. IBC 2012 1808.3 requires the use of the most conservative loading, and while it permits reducing live loads, that would not apply here. ("Foundations shall be designed for the most unfavorable effects due to the combinations of loads specified in Sections 1605.2 [strength design] or 1605.3 [ASD]...")