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Wood Stud Firewall F'c reduction

Wood Stud Firewall F'c reduction

Wood Stud Firewall F'c reduction

(OP)
Has anyone run into this before? It came from Nation Gypsum Association's ESR Report #1338


4.2.1 General Fire-resistance-rated Design Information:
a.
The axial design stress of the wood studs used in fire- resistive construction must be reduced to 0.78F?c, calculated in accordance with Section 3.6 of the American Forest & Paper Association’s National Design Specification for Wood Construction (NDS), with the maximum design stress not greater than 78
percent of the calculated allowable stress with studs
having a slenderness ratio, le/d, of 33.

Does that mean in my NDS bending/axial spreadsheet, I multiply F'c by .78? If so it does seem to make much difference as the equations do not seem to be very sensitive to axial compressive strength unless the studs are really short. Seems E and Fb are more important. This would be for an exterior wall where significant bending and axial loads will occur.

Thanks

RE: Wood Stud Firewall F'c reduction

Yes, that limit didn't seem to make much difference in my exterior wall designs seeing wind loads but will change interior rated walls controlled by gravity. That limit is also given in IBC table 721.1(2) foot note m.

RE: Wood Stud Firewall F'c reduction

(OP)
Thanks Wallache

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