Crane Rail Support Beams - Deflection Limits 1

[Nulukkizdin]

Working through a retrofit of an (E) steel fabrication building. The original building sports a 20T crane that runs along rails supported at 20'-0" OC. In the proposed retrofit, the architect is showing two of those columns being removed, creating a 60'-0" span over which the crane will continue to run.

That said, I'm looking to design a (N) steel beam that will support the crane rail over this new span. In doing so, I'm curious as to what type of deflection limits I need to hold my design to. I'm assuming there will be not only a L/___ limit but also a maximum allowable deflection number?

Similarly, due to the requirements of ASCE7-10 4.9.4, I'm putting 20% of the vertical load as a lateral force perpendicular to the beam. Two questions on this:
1) My original assumption is that this lateral force should be applied IN ADDITION TO the vertical load on the crane, is this correct?
2) Similar to my question above, what kind of deflection limits should be imposed on the out of plane loading case?

Thanks!

 

[JAE]

Your best bet would be to get AISC Design Guide 7 - that has criteria for crane runway design including recommended deflection limits.

Can be found here: AISC Design Guide 7

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[txeng91]

For the lateral load, it is 20% of the crane capacity including the hoist and trolley weight, (just the parts that actually move laterally) so you can exclude the weight of the crane girders. This lateral load would definitely coincide with the maximum hoist load of the crane system. I believe it is produced by wheel friction and/or swinging of the suspended load, both of which are a function of the carried load. You would need to size the cap channel on the crane girder to take this load and span 60' between the columns, which might be an issue, maybe see if you can use the cap channel in conjunction with the top flange of the beam for added strength and reduced deflection. I'm not sure what the allowable horizontal deflection would be but for the vertical deflections the ASCE 7 specs different parameters for different classes of cranes, so you would need to determine the crane class first. I think the highest deflection allowed for light duty cranes is L/600, so 1.2" over a 60' span. Not sure if that would be an issue or not. I would contact the manufacturer of the crane and see if they have any recommendations on horizontal or vertical deflections. Last time I did a retrofit on a crane I found the Canadian guide pretty helpful, lot of good info on connections and details, see link below

http://www.cisc-icca.ca/files/publications/techpubs/design/craneguide/CraneGuide2E5P.pdf

 

[Agent666]

As a first guess on upper limits back analyse the existing arrangement and see how much further you think you can push it based on code limits.

Crane manufacturers also often have limits to which their own cranes can operate.

 

[thaidavid40]

You probably ought to also look into the guidelines given in the AISE TR-13, too. For 20 tons and 60 feet, you might do better with a truss, or a plate girder.
Dave

Thaidavid