Crane Column Cap Plate Material Grade

[B16A2]

Cap plates on columns that support runway girders should be flexible enough to allow the ends of the girder to rotate. (pinned ends)

This means, the plate has to be thin enough to prevent yielding the extreme fiber so it always remains in the elastic range...or so I believe. Would any of you bump up to grade 50 plate material in order to not have an overly thin (<3/4") cap plate? Grade 50 is less ductile, but if its kept in the elastic range I'm not sure it'd be a problem.

You can easily meet all normal girder deflection requirements and still have an end rotation on the order of 0.005 radians.

 

[dik]

I'm not sure it matters that much, thickness would have some effect on the 'flexibility', but yield strength would have little effect. I use cap plates to support continuous members; for others, a web or flange connection without the plate is normally used.

Dik

 

[hokie66]

Crane girders are normally supported on cap plates, but the support is actually over the column flange, as the beam and column webs are in the same plane. I see no reason why the yield strength of the cap plate matters.

 

[B16A2]

I believe it matters from a fracture point of view when you're trying to prevent material from strain hardening. Grade 50 can bend farther before creating plastic regions at the top and bottom of the plate.

 

[B16A2]

Note, to prevent prying on the bolts that fasten the crane girder to the cap plate, they must be located outside of the column flanges. (the girder will rotate about the stiff column flange) If not you start breaking bolts at the girder end rotates.

Therefore, you have to cantilever out your cap plate, which has to bend with the girder. All of this is standard crane construction in AISE, DG7, CISC,...they say to make sure the cap can sustain the rotations, but give no guidance on fracture.

If anyone has access to Fisher's paper on cap plates from the early 2000's let me know.

 

[hokie66]

I hear what you are saying now. But I have never seen the bolt breakage occur with bolts inside the flange. Fisher's 1979 book shows the bolts inside. Will look into it further. A lot of these runway details are the result of experience over the years, and different folks have had different experiences.

 

[hokie66]

I looked at some of Fisher's papers, probably not the one you meant, and for the detail with the bolts outside, he just says "the cap plate should not be overly thick", or something to that effect. Not much guidance. But for a detail where flexibility is necessary, I would be inclined to stick with the A36 steel. Why would yielding be detrimental in this case?

For lighter duty cranes with the bolts inside the flanges, I think leaving the bolts loose is good practice. The note was "finger tighten, back off 1/4 turn, and provide a lock nut". For heavy cranes, we used to do a rocker detail with the runway girder end plates bearing and a gap under the girder flange. A similar detail is shown in the CISC runway guide. A caution though, in some facilities, that type detail can lead to corrosion problems.

 

[apsix]

It's fatigue and not fracture due to exceeding yield which will usually be the problem for crane supports.
I'd recommend that design should ensure that stress remains well below yield.
Usually a higher grade steel will have limited, if any, increase in fatigue resistance.