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RE: Main Wind Force vs C&C Wind Force

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I’m not a senior associate either, so my input may likely be worthless for your endeavor, but yes, you are correct – even further, the strength of studs doesn’t need to be evaluated for CC, but rather only deflection using 0.7*CC.  (see the footnote deflection limits section/table of the IRC)

If CC in combined loading were required, there would not be a single home in Florida standing today…  I know this from working with two engineering firms who hold a majority market in the greater florida area, which both use this approach and getting my hands on numerous go-bys from other engineers who use roughly the same designs (simple assumption that they are taking the same approach)

I will say that EVERY engineer that I have worked with (I’m a specialty engineer, so that’s a fairly big number) has a different take on the split between CC and MWFRS – so good luck convincing him otherwise.

 

FYI – my take is that any ‘single members,’ or components and connections (any connections which will not behave as part of system – i.e. if that one connection fails the system will go flying –

 

For a closed structure generally anything which maintains the envelope of the structure from becoming a ‘partially open’ situation is CC – even this gets quirky when discussing the difference between say roof trusses and truss plates…

 

Take the case of a canopy.  Roofing materials and ALL connections are designed to CC, the main members are MWFRS, only b/c even if they fail they will not create a projectile situation, so long as the connection holds. 

 

But I’ve had engineers split hairs and say that there is a difference between a free standing canopy and one attached to a structure… not sure what sense that makes myself, but it goes to show the crazyness out there when it comes to wind loads…

 

 


From: Jason Christensen [mailto:jason(--nospam--at)wcaeng.com]
Sent: Tuesday, October 06, 2009 11:33 AM
To: seaint(--nospam--at)seaint.org
Subject: Main Wind Force vs C&C Wind Force

 

A senior associate and myself are having a debate. 

 

So please correct me if I am wrong: 

 

Desinging a wall element for out of plane force (be it masonry, wood, etc.)

 

When checking the element for forces that are combine, (i.e. axial + wind) one should use the MWFRS forces.  However that same element must then be checked for the C&C load, but that C&C load is not required to be in combination with any other loads.

 

If this is incorrect please let me know, also if anyone has a reference that would show an example of this I would be greatful.

 

Thanks,

 

Jason