Steel Column cap splice

[tebodm]

I'm looking to extend/splice onto the top of an existing steel column to extend it through the roof level to support an HVAC equipment skid. The existing W10x49 column has girders framing into both flanges at top of column and girders framing into each side of the web at 2-1/2" below the top to support bar joists. I'm struggling with how the installer can attach a "cap" plate to the existing column to support the new HSS stub column extension. Does anybody have any good ideas? Thanks in advance.

 

[DETstru]

How many of these are there?
How about just using a W10 for the new post (instead of your HSS) and bevel weld it to the top of the existing W10x49? No cap required.

 

[WARose]

I'm struggling with how the installer can attach a "cap" plate to the existing column to support the new HSS stub column extension.

Do you have to have a cap? You could just weld the same size on top.

As far as the cap scenario goes: You don't think you have enough clearance for the welder (i.e. to weld the plate to the existing column)? Assuming that from the top of the girders to the top of the column is clear.....it should be ok for the cap plate to column flange weld. The challenge will likely come with the cap plate to web weld.

In short: with a 5" projection (of the cap plate) and 2.5" height (above the girder to the top of column).....it will be tough....but I've known welders that can do it.

A alternative might be to omit the weld to the column web and have the selected HSS member be the same depth and width as the column. In bending and tension, all the load will run from 2 sides of the HSS to the column flanges. (If you can make all that work.)

 

[KootK]

You could top side weld a couple of fitted stiffeners into the top of the column and effectively create a cap plate that way. Then slot the HSS to fit over the bit of web that projects up.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[tebodm]

Thanks for the great suggestions. I was having a brain cramp and these make perfect sense now.

@DETstru I have about 8 columns to do. I like the idea of welding the same size section on. I was stuck on the cap plate mentality trying to avoid as much field welding as possible and was thinking the HSS for easier roof flashing/termination but I think we can work with the W-shape stub.

@WARose I was struggling with the clearance for welding the plate as well. Think I will proceed with stubbing thru roof with same column profile as below.

@KootK I like the idea of fitting web stiffeners into the column and it could be done easy enough from the top side. If I idon't go with the full weld splice using the same column shape, this is the route I think I'd go.

 

[hokie66]

Another way, if the numbers permit, is to provide your new post with a base plate which welds to the top flange of the beams which frame to the column flanges. Not a direct load path, but it would be simple to do.