Built-up Crane Runway Girder

[Andrewstructure]

I have a client who has modified his crane runway beams with plates connecting the edges of top and bottom flanges of the plate girder (see attached image). He wants me to analyze the section to determine an allowable crane capacity.

My plan is to ignore the interior web and analyze the section as a box section, using AISC LRFD section F7.

Any comments?

http://files.engineering.com/getfil...4-490b-a981-07649656f7b6&file=Runway_Beam.jpg

 

[ToadJones]

I'd certainly investigate the original web as far as shear goes. The new webs are out-of-plane for shear loading and may take a more rigorous analysis.

 

[ToadJones]

This is a weird modification and it looks to have been a costly one.
Why did they do this?

 

[paddingtongreen]

I wonder what happens at the supports. Do the plates stop for top flange bracing? Interesting.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[apsix]

paddingtongreen's comment re what happens at the supports is important.
All that additional torsional strength might not be worth much if the boxing doesn't continue for the full length.

 

[Andrewstructure]

They just added the reinforcing because they had steel and welders employed at the company.

The plates were added due to serviceability concerns.

In the design, weak axis deflection is the controlling factor. I am planning on using the exterior web plates only for lateral analysis.

If it becomes necessary to use the exterior plates for strength I would have to assume that the interior web cripples before the exterior webs are utilized, essentially eliminating the interior web in my design. Does this sound reasonable?

 

[ToadJones]

I'll just say this....Your rail lies directly over top (or should) of the original web. I don't think eliminating it from your analysis is possible.

 

[paddingtongreen]

I doubt if there was much, if any, load on the girder when the plates were added so you might be being too kind to the plates if you assign a crippling load to the web and then share the balance between the plates. I would suggest that you check it that way and also when all three elements share the load by area, and use the worst result.

I'll be interested in how you calculate the shear in the welds for weak axis bending with that sloping plate.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[MikeHalloran]

Rail is often attached with hook bolts over the flanges of the runway beam or its cap channel. There are other ways, of course, but the pictured boxing plates would interfere with hook bolts. So, how are the rails secured?



Mike Halloran
Pembroke Pines, FL, USA

 

[JAE]

Don't forget fatigue checks on the welds.

 

[FLCraneBuilder]

Side plated WF's have been commonly used for crane bridge girders many many years. The sloped side plate seems rational.
However, when we do these - we end up having to provide diaphrams on approx 72" centers due to web buckling. Assumes 1/4" webs. If thicker, this might go away.