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Steel columns in 4 storey wood frame building - shrinkage issue

Steel columns in 4 storey wood frame building - shrinkage issue

Steel columns in 4 storey wood frame building - shrinkage issue

(OP)
I am working on a 4 storey multifamily wood frame building and have to put some steel columns from transfer slab elevation up to the roof to pick up some heavily loaded steel roof beams (Pf ~ 250 kips). The project is on a ski hill with roof snow load of 300 psf.  The problem we have is that the shrinkage of the wood frame will cause the steel columns to "poke" thru the roof.  While we don't expect any structural damage, there will be an issue with the drywall on the top floor directly adjacent to the column. Each floor level will have 4 plates for a total of 16 plates, so we can expect about 1 1/2" of shrinkage by the time we hit the 4th floor.  I do not plan to connect any wood frame elements to the steel columns on each floor.  Does anybody have any details that we could try to minimize this damage?  

RE: Steel columns in 4 storey wood frame building - shrinkage issue

Use engineered wood products (PSL, LVL, TJI, etc.).  They dont shrink.

RE: Steel columns in 4 storey wood frame building - shrinkage issue

(OP)
Are you suggesting engineered wood products for all of my stud wall assemblies?  The source of the shrinkage is on the top and bottom plates of the stud walls....

RE: Steel columns in 4 storey wood frame building - shrinkage issue

Use them where ever you may have a shrinkage problem.  Trus Joist now makes an engineered wall stud that is "straight and true".  Maybe use them for your top and bottom plates?  I believe the product name is TimberStrand LSL.  Trus Joist at 1-800-628-3997 I'm sure would be more than happy to help.  Unfortunately, I think the studs cost about twice as much as a regular solid sawn stud.

RE: Steel columns in 4 storey wood frame building - shrinkage issue

The engineered lumber is a good idea.  

A couple of questions for kme though:

If the column is 40'+ tall and the wood framing is not connected to the column, then how is the column braced? If you have beams connected to the column, and the wood framing rests thereupon in some configuration, then why would each floor not act independent of the rest?

Have you considered steel studs and plates with engineered lumber floor joist bands?  Like materials will behave similiarily, but again my first question comes to light.  

Can this be designed so that the column 'floats' independent from the wall, in other words can you frame a loadbearing stud wall from the FFE to the 4th floor ceiling elevation 'around' the steel column and integal with the rest of the framing?  I don't know that this is a good idea, but I am having a problem figuring out why the floor framing is not connected to the column in some fashion.

Can you explain a bit more, it might solicit input from others. Also, can the roof framing be furred out to accommodate this movement ie, leave a space between the top of column and roof sheathing.

RE: Steel columns in 4 storey wood frame building - shrinkage issue

(OP)
You are correct, the columns are 40 ft tall. Thru each of the 2nd, 3rd and 4th floors, they will be laterally braced by the floor sheathing. However, it is not my intention to attach any of the lower floor levels to the steel columns in any fashion. Therefore I expect the problem will only be present on the 4th floor.

I have seen some examples where other engineers have put built up plates below the steel columns (ie. 16 plates for a 4 story building!). However, my column loads are such that this approach would require massive baseplates to control the wood bearing stresses.

I think my only options at this point are:
1) crown moulding on the 4th floor - crown mouldings would only be fastened to the ceiling and i would leave a deflection space of 1 1/2" between the cieling and wall gyproc.

2. Frame a false ceiling for the 4th floor, makeing sure this it is not fastented to any of the roof trusses (total roof area is about 28,000 ft2)

I can also mitigate some of the shrinkage by using D.Fir plates (normal framing species is SPF) with carefull attention to moisture content. Maybe I should also fabricate my columns 1/2" or 3/4" shorter than what they should really be?

Anymore thoughts anybody?

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