Achieving 10mm crane rail support deflection limit while not overdesigning the column and footing? 1

[FLR84]

Hi everyone,

I am designing a 22m span gantry crane shed with 6.4m bays and a crane rail support at 8m above the footings. There will be two 10 tonne cranes running next to each other.

If I model the column bases as pinned, then the footings can be regular pad footings but the size of column required to reduce the deflection at the crane rail level to under 10mm is insane. (500UB).

If I model the column bases as fixed, then the deflection limit can be achieved with reasonable sized columns, but the pad footing size required to resist the bearing due to moment (200kNm) is crazy.

I see other engineers using regular sized pad footings (~1.3m by 1.3m by 600 deep) and lighter columns than what I'm calculating even with fixed column bases.


Is my approach to this wrong? Is there a better way to model it?

Thanks everyone.

 

[straub46]

I think the lateral deflection you're trying to hold at 8m is unreasonable. That's L/800 of the column height. The beams that support the rails are generally only designed for L/800 vertical deflection and usually L/400 lateral deflection. But that's for the beam itself, generally the column deflections are held to typical building drift limits (L/240ish).

What lateral load are you using? You should only be using 100% of one crane or 50% of both for multiple cranes in an aisle (or adjacent aisles).

 

[JStephen]

X-bracing between columns? Increase size/depth of beams at top?

 

[FLR84]

I think the lateral deflection you're trying to hold at 8m is unreasonable. That's L/800 of the column height. The beams that support the rails are generally only designed for L/800 vertical deflection and usually L/400 lateral deflection. But that's for the beam itself, generally the column deflections are held to typical building drift limits (L/240ish).

What lateral load are you using? You should only be using 100% of one crane or 50% of both for multiple cranes in an aisle (or adjacent aisles).

Yes you are right. I downloaded the new standards for crane rails here and the lateral deflection limit has been increased to H/300.