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Re: Re: Nailed Wood Truss and Purlin Connections

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From: Dave Gaines <gainesengr(--nospam--at)earthlink.net>
Date: Tue Jun 13 09:14:06 CDT 2006
To: seaint(--nospam--at)seaint.org
Subject: Re: Nailed Wood Truss and Purlin Connections

 I don't know about the quality of lumber there, but its bad enough here that I'd be a bit suspicious of the connection due to the splitting problem.  Using such a small piece of wood, I'd be much happier to see a predrill and a wood screw instead of a nail for the simple reason that I wouldn't want to have to check each and every piece for the potential split.  Other than that, I'd don't see anything wrong with the connection, (assuming it qualifies to resist the load by calc).

Don

I'm glad you mentioned the   splitting problem - that was my first thought when I saw the connection.    
tiger(--nospam--at)palaunet.com <mailto:tiger(--nospam--at)palaunet.com>
      -----Original Message-----
From: Dave Gaines     [mailto:gainesengr(--nospam--at)earthlink.net]
Sent: Tuesday, June 13, 2006     1:52 PM
To: seaint(--nospam--at)seaint.org
Subject: Nailed Wood Truss     and Purlin Connections

    Terengue,         I believe you have to use the nail capacity     value from NDS for the plywood truss connections.  Reduce the value by     0.9 for dead loads.  Use the tables with a side board of whatever     the plywood thickness is and whatever the wood species is as the     side material.  Or you can use the NDS formulas to calculate     the nail value.  Check the actual nail size by pulling a few and check     embedment depth too.  If the values come even close to what the truss     demand is, you may be in the ballpark and can check it by a more detailed     method if necessary.  Of course, you need to do the truss analysis to     know the demand.         For the 2x2 holdown connections, again, check     the nail capacities by NDS.  If the 2x2 is end-nailed, the nail value     goes way down, per NDS.  If the small wood members are split by     the nailing then the nail may have no value.  Check all parts of the     connection.  You can ask for a mock-up of the connection in a frame or     jig that you can test with dead weights.  You can design a test rig to     test the connection.  Is the factor of safety for nail connections     around 8?  If so, divide the average breaking strength by 8 to get a     useable design value.  Why not add the hurricane straps     anyway?         Dave Gaines    Pasadena, CA          ----- Original Message -----       From:      Terangue       Gillham       To: seaint(--nospam--at)seaint.org       Sent: Monday, June 12, 2006 5:50       PM      Subject: Wood Truss and Purlin       Connections      
      All:             Does anyone know of a source for reference tables       describing allowable loads for nailed plywood truss connections?  I       am being called upon to do a lot of house plan reviews for local banks and       this material would be useful in cutting down my time spent on       them.             A second question regarding the use of 2x2 for       holdowns at roof purlin-rafter connections.  Is it fairly       common to place a 2x2 vertically, top nailed to a 2x3 purlin       (flatwise) running across the top of the rafter, 2x2 is butted up against       sideface of rafter and nailed in?  I saw this detail for the first       time yesterday on a house that I had Simpson type hurricane clips       specified for use, and I need to ensure that the holdown connections will       be effective.             As far as wind loads go, we use 100mph winds,       1994 UBC, so the loads aren't that bad.             Any comments from those that do a lot of wood       design would be much appreciated.                           
Terangue *Tiger* Gillham, PE
GK2,       Inc.

tiger(--nospam--at)palaunet.com <mailto:tiger(--nospam--at)palaunet.com>
               


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