Adjustment Factors 1

[SteelPE]

I am designing my first wood structure (a garage) and have a question about the adjustment factors. Currently I am designing a 2x6SPF No 2 stud for an exterior wall. As far as I can see, under to worst loading combination, I have the following adjustment factors.

CD = 1.6 (wind case)
Cf = 1.3
Cr = 1.15

When I multiply these together I get an increase of the allowable bending strength of 2.392x the base design values. This is quite large…. Is this correct for this condition?

Sorry about the simple question.

 

[JAE]

Yes but only for the D+L+W or D+W load combinations and only for Fb. Fc has a different CF factor (1.1)

You also have to check for the D+L condition without the Cd = 1.6 case. You'd use Cd = 1.0.

 

[Ron]

JAE...as usual you are da man!

 

[cg3375]

Is there an allowance or duration increase allowed in shear capacity when designing a wood moment frame in place of a shear wall (with wind only) for either the top plates or header such as the 1.4 allowed in panels per IBC section 2306.3.2?

Example, SYP #2 as my top plates has a value of 90 psi. Can this be increased for a wind only collector and if so how much (1.4, 1.33, 1.6)?

Any opinions or thoughts are appreciated.

Thanks !

 

[JAE]

You should start a new thread.

 

[abusementpark]

SteelPE,

Be sure to be cognizant of the additional wall stud bending increase factor in IBC to use in lieu of Cr = 1.15. I believe it is 1.35 for a 2x6 and 1.5 for a 2x4.

I can't recall the exact provision right now, but it is in the wood section of the code. I would check that out to see if it applies to what you are doing.

 

[SteelPE]

abusementpark

In the part of the country I come from we don’t use the IBC…. We only use a state interpreted version of the IBC… and the adjustment factor only applies to studs spaced ano more than 16” o.c. My studs are spaced at 2’-0” o.c. (forgot to mention that above).

Not being used to wood design, I was just shocked that the number was so high (and it looks like you can go even higher for some cases).

 

[FSS]

Don't forget the allowable deflections from wind. Depending upon your wall finish these can be the controlling factor and not stresses.