Steel beam supported with a wood column: 1

[nuche1973]

Howdy all. I am working on a wood framed apartment building. The floors are wood joist on wood load bearing walls. The corridor between units is metal deck and concrete. Large open areas in the corridor are desiged to be W-sections on HSS columns. As a VE item the architect wants to change the columns to wood (to negate the fireproofing cost). Size and span are factors in the beam selection. Steel is best for the deflection issues (L/360)and available depth (9" after allowing for mech ducts, concrete & deck). Is supporting steel beams on a wood column (probably a parallam or similar)accepted? I'm using IBC 2003 and haven't seen a definiative "yes" or "no". Any comments will be appreciated. Thanks.

 

[jhoulette]

Yes Dik
But the steel columns do not bear on plates right?
So you still have shrinkage across the grain at each plate, several stories it adds up.

Jim Houlette PE
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http://www.evstudio.us

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[dik]

It's a matter of detailing around this. Many old 8 and 10 storey warehouses had wood beams and columns. They minimised movement by having cast beam seats bearing on columns. I had understood he had steel beams and wood columns... little difference IMHO. Dimensional stability would not likely be an issue. Floor to Floor movement should be accommodated by detailing.

Dik

 

[msquared48]

It's not just the plates, it's mainly the floor joists that contribute to shrinkage unless engineered joists such as TJIs are used. If solid 2X10's are used, that's 9.25" of depth subject to shrinkage as opposed to 4.5" of depth for three plates per story.

So, 2/3 to the joists, 1/3 to the plates of the total shrinkage seen.

Mike McCann
MMC Engineering

 

[dik]

It's still a matter of detailing. You accommodate the change in floor height from xxx to xxx +/-. Say the plates shrink 1/8" total and the joists shrink 1/2"... You have increased the floor to floor height by 3/8" (numbers pulled out of a hat). It's still a matter of detailing; the problem is there whether you have steel columns or wood columns... IMHO.

Dik

 

[dik]

I should add that it is common practice when framing wood joists into steel beams that the top of joist is typically 1" above the top of beam to prevent a 'hump' in the sheathing. Still a matter of detailing.

Dik

 

[apsix]

Could someone clarify thanks? I'm not in North America.

All this discussion about shrinkage; is that because the non-engineered timber that you use is not kiln-dried?
I would only consider shrinkage if using green timber, and that would be very unusual where I am.

 

[msquared48]

The lumber used here should be kiln dried if spec'd, but unless you spec it, you may not get it.

Even at a moisture content of 19% or less, kiln drying, you will still get shrinkage. The effect should not be ignored, especially relative to finishes.

Mike McCann
MMC Engineering

 

[apsix]

OK, thanks Mike.

 

[nuche1973]

I guess I should add some variables into this discussion:
-Due to cost we are using 2x material (southern yellow pine for joists, SPF for studs/columns).
-Any "engineered" lumber is kept to a minimum, again for cost (this is at the Archy's direction)
-We wanted steel beams/steel columns, but the Archy pushed the steel/wood combo, citing cost due to fireproofing.
-I only have 24" to work with, this includes conc. slab,mtl deck (5 1/2"combined), HVAC ducts (9" with insulation) and the support structure (?).
-Average beam spans are 13' with L/360 deflection limits (based on the deck/slab).
I'd like to thank everybody for your input. It is truely appreciated.