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Wood Supporting Masonry or concrete? 1

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Ian999

Civil/Environmental
Mar 6, 2001
3

Section 2304.12(IBC 2000) and Section 2307(UBC 1997) says: "Wood members shall not be used to permanently support the dead load of any masonry or concrete."

Situation: 3" concrete floor slab.

What is the reason the building code has precluded wood walls as supports and not allowed the engineer to use engineering judgement? (Possibility is creep or rot but couldn't this be accounted for in the design?)

 
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It is because of the "hidden" nature of the structural support and the potential for rot, creep, and deterioration from contact with concrete. The parameters are too variable and nebulous to be reasonably accommodated by engineering judgment.
 
Exception #1 of the stated UBC section allows wood framing to carry up to a 4" thick, non-structural, masonry or concrete floor or roof surfacing. I often design garages on downslope lots with a 3 1/2" concrete slab supported by wood framing.
 
We some times support brick veners (non-structural) on 5"x5" steel angles lagged to wood walls. These are used support the brick walls over roofs. Then this is not legal?
 
boo1...attaching a steel ledge angle to wood is not a problem. It's only when cementitious materials (concrete, grout, mortar) are in direct contact with wood in a structural application that a problem exists.
 

To prevent the concrete from contacting the wood bearing wall a piece of felt could be placed to act as a barrier. The way the code reads however, it seems as if wood walls are barred completely from any load transfer in regards to concrete. (This pertains to structural concrete, also depends on the definition of structural)

Wood bearing is allowed in residential construction in the IBC but not sure in the UBC.







 
Ron:
Now you've got me confused....I've argued many times with my architects that no way shape or form can brick veneer be supported by wood members. UBC 97, section 2307 states:

"Wood members shall not be used to permanently support the dead load of any masonry or concrete".

Then the exception:

"Veneer of brick, concrete or stone applied as specified in Section 1403.6.2 may be supported by approved, treated wood foundations when the maximum height of veneer does not exceed 30 feet above the foundations. ....

So veneer can be supported by a treated wood foundation, but not by a steel angle bolted to wood framing. That's how I interpret it. Now I would probably agree with you that the "problem" is with cementitious materials weeping moisture into the wood...but the code doesn't allow it.
 
JAE...my reference was primarily to ledge angles supporting brick veneer over wall penetrations such as windows/doors in residential applications. In these applications, the ledge angle is an "assist" to the coursing bond of the masonry and doesn't take all the load.

IBC 2000 (Section 1405.5) allows this application provided the masonry does not exceed 40 psf and that the angle is attached to the wood studs with lag bolts.
 
In the IBC...makes sense there. But do you agree that under the UBC you technically cannot do this?
 
JAE...yes. Another example of code disparity!
 
I believe that the intent of the code is that no concrete can used as a structral element supported by wood construction. However if the concrete is a slab not acting as a horizonal diaphram or shear wall it is permitted. Such as elevated non-structral slabs. It should also be noted that the weight of the concrete which is usualy high need to be accounted for in both lateral and gravity calculations.
 
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