Appropriate use of cap plates for W-shape columns w/ shear connections

[redsouther]

In our office, we have a "rule of thumb" that cap plates are typically provided at the top of all wide flange columns in structural steel framing, unless there is a compelling reason not to do so (erection issues, etc.) - even those with beams framing into the flanges and/or web only.

I haven't been able to find any justification for doing this in the code, or any of the AISC guides, and the only explanation we seem to be able to give is that it "helps the top of the column resist twisting and maintain its shape" if not otherwise braced by a concrete slab or roof diaphragm.

This happens fairly frequently in industrial buildings and support structures for equipment, and it's just something that we've always done. Most of the typical details I see in older detailing manuals always show cap plates as well. I'm wondering if anyone else has a similar rule of thumb, or if you've heard of more substantial justification for when cap plates are appropriate for columns in this condition.

 

[BAretired]

I would not use a cap plate on a WF column unless I wanted to bear something on it either now or in the future. It seems like a needless expense.

BA

 

[JAE]

I suppose if you have a single plate shear connection coming into one side of a web, the potential rotation of that plate due to vertical shear from the beam reaction could conceivably bend the web out-of-plane.

Twist - I don't see it. The column itself has no forces initiating any global twist and a cap plate wouldn't resist that at all as it is simply connected to the twisting column and goes along for the ride.

Warping of the flanges relative to the web: Maybe - but again, what sort of force is initiating this warping? I can't see it.

 

[delagina]

Cap plates for columns in industrial industry for equipment structures are used for lifting. many of these structures are modules. built off-site then shipped, transported and lifted as 1 modular structure.

 

[connectegr]

For top of column conditions with shear only connections, cap plates should not be required. Without the cap plate erection of the beams to the column web, at the top and lower levels, can be simplified by working the beam between the flanges with without interference. If moment or axial loads are present in the top of column connections, then the cap plate may be required.

http://www.FerrellEngineering.com

 

[csd72]

I disagree with others above that say that it is definately not required and would say it is a good idea but not always essential.

It depends on the exact configuration:
If the beams framing in either side are unrestrained then I would consider putting in a cap plate.
If the beams either side are restrained by joists, purlins e.t.c. then The column is restrained against any rotation and I would therefore not see any need to put it in.

The forces causing warping are the restraint forces and the eccentricities of the applied loads as well as any secondary stresses from out of straightness of flanges e.t.c.