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RE: Nailed Wood Truss and Purlin Connections

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Tiger,
 
Any idea of methods used in Guam?
 
Michel Blangy, P.E.
Design Engineer
-----Original Message-----
From: Terangue Gillham [mailto:tiger(--nospam--at)palaunet.com]
Sent: Tuesday, June 13, 2006 4:06 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: Nailed Wood Truss and Purlin Connections

Dave:
 
Thanks for the reply.  As far as why not just use hurricane clips, it's a matter of supply.  I live and work in Palau, and that's an awful long ways from you guys which makes shipping things VERY expensive.  Another big part of it is that the construction industry here is still "old school".  We don't get a whole lot of typhoons (unlike Guam to the north), no appreciable seismic activity either, and we haven't had a true building boom as of yet.  All this added together means that contractors pretty much use the same method of doing things that they have for the past 30 years.  Metal connectors are just beginning to make an appearance here, and if they do get carried by the local stores then I will specify them.  Otherwise, it is useless to specify something that they cannot obtain and use.
 
Of course, I could always start importing them...
 
I'll look over your email and see what I can do.  I'm glad you mentioned the splitting problem - that was my first thought when I saw the connection.  I need to figure out a different way of doing that, since I don't relish the thought of clambering up on the roofs of all of these houses to check the entire thing for split 2x3 purlins.
 
Regards,
 
Tiger
 

Terangue *Tiger* Gillham, PE
GK2, Inc.

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 -----
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>