Thoughts on tall CMU columns

[Antnyt23]

I was asked if it was feasible to use a 25' tall reinforced cmu column in an atrium. The columns would be surrounded by glazing on both sides with bond beams at the mid height and top. Initially I thought it sounded a little tall for a cmu column, however, I ran some numbers just as a gut check to get an idea and it seemed fine. I just wanted to hear some opinions on this. I don't commonly use tall CMU columns.

25' column taking approximately 10' of trib wind area at approximately 28psf(already factored by .6 for asd). The columns would have a bond beam at midheight for the first floor, however, it would not have bracing in the other direction for the full 25'. I assumed simply supported column with effective height of 25'.

I assumed a 16"x16" column with 4 #6, f'm=2500psi, fy=60

H/t = (25)(12)/15.63 = 19.2 which is acceptable

Using the load combination of D+.75W+.75Lr and my total moment including accidental moment due to eccentricity came out to approximately 17.32k-ft
Axial load at midpoint of approximately 14kip.

I developed a P-M diagram and the loads fell safely within it. Double checked some masonry and steel checks and everything seemed like it should be adequate.

Just wanted to see thoughts on any possible issues that could arise or items that I may be overlooking.

 

[Antnyt23]

Forgot to mention that I did also check the buckling of P<1/4Pe using the minimum accidental eccentricity and will recheck if actual eccentricity is determined to be greater than the accidental assumption.

 

[theonlynamenottaken]

Have you checked deflection of the column with respect to a maximum recommended deflection for the glazing? I'm unclear on how its braced or connected to a floor diaphragm at mid-height, but if it could be considered to deflect over a 25' span I'd wager that you're exceeding or approaching the limit for the supported glazing.

 

[Antnyt23]

Thank you. I will make sure to look into the deflection issue you mentioned (ill make some conservative assumptions for an initial check for the glazing deflection).

Just FYI the columns will be surrounded by glazing for an atrium. It will be a two story building, however, in this area the columns will be unbraced in the primary axis running from ground to roof(spanning 25'). The axial loads on them will be fairly low (unless the truss design changes), however, they will be subject to a larger moment due to the wind acting on the glazing around them.

 

[jayrod12]

It would likely be easier to use a steel column that's wrapped in masonry veneer. They could attached masonry ties directly to the column.

 

[Antnyt23]

agreed jay.... initially the preference would be masonry if it would work. Was interested to see if anyone ever used tall masonry columns like this and if so any problems they were familiar with. I personally am use to using steel. Just wanted to kind of gain some information on tall masonry columns and issues that may come with them.