Choosing Columns For Splices

[marinaman]

I am designing a (5) story building. I would like the community's opinion on column selection when considering splices.

An example of what I'm talking about is where, by calculation, the column size required is W14 x 138. I plan on placing a column splice 4' above level 3. When looking at possible column sizes in the length from the top of the splice thru the rest of the height of the building, I could select lighter W14's or go to W12's. That being said, what do you guys think about matching column plan geometries versus splices requiring bearing plates and spacer plates.

When considering cross section geometries, do you guys try and stay within the same column series (W14's), 14's with just the same "T" dimension, or ignore all this and just pick the lightest column and use whatever bearing plates and spacer plates needed.

My gut tells me to select the same series, W14's, just lighter, for direct load transfer thru flanges and web. BTW...many of these columns are involved in concentrically braced frames.

Opinions are appreciated.

 

[txeng91]

I'm in the same boat, 5 stories splicing above the third floor. After doing some research, I'm deciding to keep the same column dimension so that gravity loads are transferred through bearing rather than the connection. Ideally you want to stay within the same column group (the sizes that are grouped together in the steel manual) because they all have the same distance between the flanges so you get 100% bearing area and you can shim out the difference in depth. With that you can just use the typical column splices shown in the steel manual and not have to worry about sizing any connections, except at the braced frames. I did a check I think they have around 75-100 kips of tension capacity which work with my frames, but if you have narrow frames with a lot of uplift you might have to beef up those connections. The manual only seems to specify 3/8" flange plates w/ 6 bolts to each column and no web plates, which I find odd. I;m thinking of going to 1/2" flange plates and web plates w/ 2 bolts to ea column.

My only issue is that there are some stacks where my bottom column is already at the bottom of a column group so I am transitioning from 12" wide columns to 8" wide. On the AISC tables they specify a bolt gauge and plate width for depending on the column width. Do I just use a flange plates to match the 12" wide column and use a larger bolt gauge at the bottom than the top or do I use a flange plate match the 8" wide column and use the smaller bolt gague to match the smaller column on both the top and the bottom. Ill keep researching and let you know if I find anything.