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RE: Valley Rafters

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Randall,

Stick with industrial, residential work is a black hole you may never be able to escape.

Joe

 

Joseph R. Grill, P.E. (Structural)

Shephard - Wesnitzer, Inc.

Civil Engineering and Surveying

1146 W. Hwy 89A Suite B

Sedona, AZ  86340

PHONE (928) 282-1061

FAX (928) 282-2058

jgrill(--nospam--at)swiaz.com

 

-----Original Message-----
From: Randall Moore, PE, SE [mailto:ranmoo(--nospam--at)ec.rr.com]
Sent: Monday, September 12, 2005 12:36 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Valley Rafters

 

In that I have a strong interest in moving towards more residential design / analysis (from a background exclusively heavy industrial) and from reviewing this thread, there seems to be a myriad of ways to look at residential component design.

 

Can you recommend resources (TEXT BOOKS, design guides, software, etc.) that can be used to design the components of a residential structure.

 

Waiting for "Ophelia" in Southeastern NC!!!

 

TIA

 

Randall Moore PE, SE

Wilmington NC

 

----- Original Message -----

Sent: Saturday, September 10, 2005 2:02 PM

Subject: RE: Valley Rafters

 

Thor,

 

The design of a valley has more to do with the connections than with design of the member itself.  And it has to do with the roof structure as a system. The components of the system include the rafters, the ridges, valleys and hips, and the continuous double top plate.

 

In a rational and properly designed roof system, only the rafters need to be designed for flexure.  If the rafters are tied in each direction, their axial components of force resolve into an axial force in the valley or hip, so that neither the valley nor the hip acts as a beam.  However, as you follow the axial forces through the system, the forces at the connections can become pretty large, and even unmanageable.  And it can become impractical to tie rafters in each direction.  If you can’t follow the axial forces through the system and resolve them all with designed connections, you should not hesitate to design ridges, valleys and/or hips as beams.

 

The conventional light-frame construction rules for framing can result in roof systems that cannot be rationalized.  Nevertheless, they seem to work O.K..  If they are not magical, perhaps, as Barry suggested, it has something to do with the buttressing or diaphragm action of the sheathing.  I have not figured out how to take advantage of the action of the sheathing in a gravity-load design of a roof-framing system.  

 

Nels Roselund, SE

South San Gabriel, CA

njineer(--nospam--at)att.net


From: Avicpeng [mailto:vicpeng(--nospam--at)telus.net]
Sent: Friday, September 09, 2005 3:04 PM
To: SEAINT
Subject: Valley Rafters

 

And just to start ... does anyone design the valley rafter of a roof, or do you write it off as "standard framing"?  If not, why not?  If so, why?


Thor Tandy P.Eng MIStructE
Victoria, BC
Canada
vicpeng(--nospam--at)telus.net