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RE: roof truss daiphragm forces

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Hi Tim,

 

It’s not commonly done.  Tell your plan checker to look at the diaphragm in the other direction, or perpendicular to your trusses.  Will he require continuous drags at some spacing in that direction also?  Even if it is a fully blocked diaphragm, in the transverse direction those blocks would be broken every two feet, why is that any different? There are other ways to look at it but this might be the easiest to help him understand.

 

Otherwise, it sounds like its time to “pull rank” as the engineer and say “no”.  (You could add that you did consider his position first…)

 

Truitt Vance, P.E.

 

 


From: Pinyon Engineering [mailto:Pinyonengineering(--nospam--at)hughes.net]
Sent: Thursday, May 17, 2007 8:58 AM
To: seaint(--nospam--at)seaint.org
Subject: roof truss daiphragm forces

 

Hi

I just went thru a plan check for a garage with roof trusses (the house color is sand)  The plan check engineer wanted me to install straps across the ridges of the trusses to account for internal diaphragm stresses.  I designed the chords of the diaphragm.  I added a note for the truss mgf to add an additional 2000 lbs tension capacity to the ridge plate connection(I calced this) (for all the trusses) instead of the straps.  I have never had this comment before.  is this commonly done? or is this guy super conservative?

 

Tim Rudolph

Pinyon Engineering

Bishop CA