Crane Runway Beam | Cantilever & Splicing

[bookowski]

Looking at a crane runway beam and have a couple of questions:

System:
- 10 Ton overhead crane (for a small steel fab shop)
- Runway beam span = 68ft, but due to site constraints the end footing needs to be held back so the client wants a +/-60ft. span + +/-8ft. cantilever

I have never done/seen a cantilevered runway beam but I have a feeling it isn't a great idea. In general I know that continuous runway beams are discouraged, and therefore the cantilever is likely to suffer from the same fatigue related issues. Has anyone done/seen a small cantilever like this?

Based on the demand and span I could get a rolled shape to work but we can't get a single piece of that length to the site. I have read that welded splices should not be used in runway beams due to fatigue issues, what about bolted splices - are those also to be avoided?

 

[dik]

I've done a 12' cantilever with 10T and no problems Splice at first interior support for shear only (no moment)... Mine stuff and SF=5 dictated.

Had to use a WT section welded to the top of the cantilever beam... stiffness an issue and also deflection.

Used Eurocodes to accommodate LTB for bottom loaded cantilever. Their LTB calculations accommodate the location of the load whether top, mid, or bot of the section.

Dik

 

[bookowski]

Thanks.

I am not able to push the splice to the first interior support, that would require a 68ft. piece which we can't get into this site. I need a splice somewhere along the beam.

 

[SteelPE]

Would it be possible to cut down on the length of the last 60'-0" bay to say 30'-0" by placing an intermediate support and splice the runway beam there?

 

[theonlynamenottaken]

Are you sure that you can get a rolled section to work with a 60' span? With a span that sizable I'd think you'd have lateral issues. Many times with crane rail spans over ~45' I've had to find alternatives to the typical "single W-beam with C-channel cap" section to get the lateral deflection, web sidesway buckling, and torsion under control, though I'm usually working with larger crane capacities. If you have to make a moment splice and you have lateral deflection issues with the large span your answer may be to design a bolted box truss. A box truss would resist the lateral thrust loads, probably result in less overall tonnage of steel, and should accommodate a bolted moment splice easier. Maybe you could sell the owner on the idea based on them doing the truss fab themselves?

Also, see this thread for some good advice/thoughts:

Link

 

[bookowski]

I am not positive but based on initial numbers it looked like it would be ok, 10T isn't too heavy. There will be a catwalk adjacent to the beam which will form a horizontal truss to take lateral.

 

[bookowski]

So I'm not seeing anyone that has done or is recommending a splice along the beam length....?

 

[bookowski]

No one has any advice on splicing a runway beam?

In the example from AISC design guide 7 they come up with a W27 + cap for a 70ft. span - for a 70ft. rolled shaped I'm assuming that it would be spliced, so I am assuming this is done. Everything I read suggests that you should not splice a runway beam, including the design guide itself. If I do a full pen and adhere to the fatigue requirements of AISC is there a problem?

 

[CTW]

I don't think there's a problem as long as you've covered all the details. But I'd suggest researching further to see if you can determine why most publications suggest not splicing a runway beam. If you find anything, please update this thread so that others can understand the reasoning as well. Researching some publications from AASHTO regarding bridge girders may help too.

Look at it this way, there are much longer spans used on crane runways which utilize plate girders. So for a 90 ft span plate girder, shorter lengths of plate have to be spliced together to create 90 ft long flanges and web. Although I would suspect that the plate splices occur at different locations.

 

[CTW]

90 ft might not have been a good example to use as I believe some plate sizes are available in that length if memory serves me correctly.

 

[chicopee]

And don't forget to weld on stop plates on the cantilever end.