Stress reduction at wood stud walls (fire-rated)

[SacreBleu]

In the UBC and IBC, there is an "obscure" footnote in the fire-rated wall assembly tables. It simply requires a reduction of allowable fc' stress (multiply by 0.78) for design of load-bearing stud walls if wall is fire-rated. (I don't have access to the Codes now, so I can't give a page or section reference).
My question- does the reduction also apply to the bearing stud (post) at each end of header/beam? If so, what about double or triple studs at ends of headers? Are those considered more fire-resistant being nailed together as a multi-ply "post"? Finally, what about any 4x or 6x post in the wall?

 

[JAE]

Can you point us to the footnote - the code paragraph reference?

 

[SacreBleu]

JAE, because of all the crises occurring regarding the movement to ban DHMO and bread <LOL>, I had misplaced the Code references, but here they are:

UBC 1997 (Vol. 1) Table 7-B, Footnote 18 (page 1-84)

IBC 2000 Table 719.1(2), Footnote (m) (page 130)

IBC 2003 Table 720.1(2), Footnote (m) (page 121)

 

[JAE]

Hmmm...difficult to say. Section 719.1 - last sentence - seems to indicate that you'd have some work to do if you did "incorporate" something into the wall.

But the footnote m refers to "studs" which I would take, technically speaking, to be the repetitive structural wood components in the wall...which would include the bearing stud and mulitiple studs on either side of openings.

But I would think that a built-up column within the wall, supporting a separate beam, would be looked at as a column, not a part of a stud wall.

 

[SacreBleu]

Since the Code has no other clues about this topic, we decided to apply the 0.78 factor to all 2x and 3x studs, irregardless of whether single or multi-ply. We set up our Excell programming to not use the 0.78 on 4x and wider posts. Since the factor is multiplied th fc', the actual allowable compressive stress was not reduced as much. The tricky thing in the Code was that any L/d ratio had to be at least 33. A 2x4 stud wall at 9' high went from L/d=30.1 to 33, which reduced its allowable a bit.
Amazing how things in the Code go unnoticed for years until a sharp-eyed plans checker catches something.