Does anyone know why wind diaphragm capacities (NDS) are 40% higher than seismic? 4

[AaronMcD]

I searched for a while and couldn't find anything except one old thread where someone mentioned a safety factor change that doesn't make sense to me, and there wasn't much info provided.

http://www.hellodwell.design

 

[rowingengineer]

I assume this is the thread you are referring too, thread337-223905

you might have to track down teh link that JAE seemed to review and understand.

 

[HTURKAK]

This snap is from IBC Illustrated Handbook ;

(As with diaphragms, the allowable shear capacities for wood structural panel shear walls
may be increased 40 percent for wind design only. As explained within the section on
diaphragms, wind loads are essentially monotonic and bounded, a safety factor of 2.0 is
deemed sufficient for wind loading. Because code tables use a factor of safety equal to 2.8,
this results in a 40 percent increase in the tabulated values for wind load design. It is simply
a coincidence that this 1.4 increase factor is numerically the same as the factor used to
convert strength level seismic loads to ASD level in the alternative ASD load combinations
in Section 1605.3.2 ..)

 

[AaronMcD]

@HTURKAK
So it does have to do with a safety factor change. The safety factor is currently 2.0
So did they decide to switch to a 2.0 factor for everything and reduce seismic capacity rather than increase wind capacity?

Seems like this would be simpler if they just tabulated the actual allowable loads, OR just used 2 different safety factors with a single table.

http://www.hellodwell.design

 

[HTURKAK]

The safety factor is currently 2.0 and deemed sufficient for wind loading. Regarding the seismic loads , still 2.8 and this figure in compliance with the (overstrength ) omega factor for the subject structural systems.