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RE: Lateral Stability of a Box Beam ?

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Check out the APA website.  They have some literature on plywood-lumber box beams that probably covers the subject.


Eric R. Ober, PE, SE


Holbert Apple Associates

3423 Olney-Laytonsville Rd., Ste. 6

Olney, Maryland  20832

(301)570-1460 (Phone)

(301)570-1462 (Fax)




-----Original Message-----
From: Bill Allen [mailto:t.w.allen(--nospam--at)]
Sent: Thursday, January 15, 2009 1:51 PM
To: seaint(--nospam--at)
Subject: Lateral Stability of a Box Beam ?


I have a situation requiring two beams, approximately 12" apart spanning about 27 feet. They aren't supporting much more than their own weight, but I'm concerned that if I just use the span as the unbraced length, the beams are going to be very large.


I would like to put plywood top and bottom to increase the effective lateral torsional strength. Is there a good reference in determining the capacity of such an assembly in wood?


Thank you,



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


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