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RE: Conventional Wood Framing

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I agree with Jordan’s comments.  >From a technical standpoint if the plan isn’t a “box” the loads don’t easily resolve themselves and additional members (beams, braces, purlins, columns, struts, ceiling beams, tension rings, etc) will be needed to support the real world conditions. 

 

Section 3.5 - Roof Systems of the Wood Framed Construction Manual provides the most usable language I’ve seen, although it is still lacking. 

 

Chris

 

Haffner Consulting Engineering

www.haffnerconsulting.com

Office & Fax:  541-478-3052

 

-----Original Message-----
From: Jordan Truesdell, PE [mailto:seaint1(--nospam--at)truesdellengineering.com]
Sent: Tuesday, August 28, 2007 8:36 AM
To:
seaint(--nospam--at)seaint.org
Subject: Re: Conventional Wood Framing

 

No, they are supported by magic.  Okay, not really magic, but a careful random combination of gwb ceiling tension, unanticipated load paths through non-loadbearing walls, and hoop stresses in the roof diaphragm.  The IBC, if I remember, is no more helpful than what you've probably found in the UBC.

If you do a diligent trace of the loads, you'll find that certain, simple geometries will work without support, but that most modern plan-book and architect-designed roofs do not work by normal mechanics. Sometimes you can get a hip end to work by making a multi-ply king post truss at the end.  Many valleys and hips use the same principal as ridgeboards, but few non-engineers make sure that all the forces resolve somewhere definable.

I believe the building codes are written to carefully avoid talking about such things, in hopes that nobody will notice (isolated/spread footings are given similar treatment in the prescriptive design code).

Jordan



Bill Allen wrote:

In conventional wood framing, are vertical members required to support hips, valleys and ridges?

 

Are there any better references which are more definitive than the single paragraph I’ve found in the UBC?

 

TIA,

 

T. William (Bill) Allen, S.E.

ALLEN DESIGNS

Consulting Structural Engineers
 
V (949) 248-8588 F(949) 209-2509

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