Wood Truss Joints

[Lake06]

Hi,

Does anyone know of a good reference book or manual to check 2x wood truss joints connected with metal plates by hand?

 

[KootK]

Start with TPI1: Link.

This may help too: Link

One manufacturer's ICC report: Link


I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[jayrod12]

Perhaps the truss gurus here can elaborate, but I've never been able to determine the capacity of the truss plates themselves, typically I ignore the fact it exists and provide a new plywood gusset to take 100% of the design load.

 

[KootK]

Ditto.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[oldestguy]

Use ring shank nails and you really got it. US Forest Products lab has published info on those nails. As I recall I allowed 100 # when I built them.

USFPL has a formula for "yield" (0.015 ") loads on common nails parallel to grain. p=KD3/2 lb/nail, Where K is 1,440 to 2200 for soft woods and D is in inches diameter. Ultimate loads approach 3-1/2 times this when tested. Ring shanks much better.

 

[BigInch]

I used to do truss designs for Clary Corp. way back in the 70's. I'd say they work pretty damn well.

Capacity Tables can be found here,

http://www.wholebuild.co.uk/assets/user/thiclirost/gn20agrement2010.pdf

 

[oldestguy]

Here is a recent USFPL paper on the subject

l.fs.fed.us/documnts/fplgtr/fplgtr113/ch07.pdf

 

[SLTA]

I once talked with an engineer at Big Truss Design Company who said they purposefully do not provide load capacities on the metal plates. They never did give a good reason why, though.

Please remember: we're not all guys!

 

[BigInch]

Most likely so nobody else could use it commercially, or hold them potentially liable for any failure. I can pretty much guarantee you that they are far better than plywood and bolts, as long as reasonable care is taken with positioning the plates during fabrication. There's more potential for doing damage to the wood while drilling bolt holes, or getting the holes too close to the member ends, plus the consequential reduction in cross-section area.

 

[KootK]

I've had the misfortune to have to pull toothed plate connected lumber apart for salvage. The capacity really is surprising. Sure am glad that I decided to go to college.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[medeek]

What type of metal plates? I'm assuming the standard metal plates you see on MPC trusses, but usually those are pressed into place with a hydraulic press of sorts.


A confused student is a good student.
Nathaniel P. Wilkerson, PE

http://www.medeek.com

 

[XR250]

I recall reading somewhere that it is about 80 PSI

 

[BigInch]

Yes good number. It would be right about 80lbs per inch of plate area.

 

[concretemasonry]

I don't think you would find reliable strengths for the plates them selves, especially if they are installed "by hand".

The basic reason is that the plates are designed to be installed in a plant location with controls and the plate manufacturers also offer truss designs supervised by professionals.

A plate manufacturer does not see a benefit to sell just the plates for unsupervised use and incur liability if they are used by a "nail bender" with no liability.

A truss is a structural component that is based on performance, controls and just as prestressed and precast concrete, unless the engineer takes chances.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[BigInch]

They are reliable if installed according to instructions. It is possible to buy only the plates in some DIY stores, but having the hydraulic, or roller equipment needed to place them properly on hand for only a few trusses would lose economy. The real benefit of these things is obtained by using automatic cutting machines to accurately cut the joining angles for each piece and shop fabricating thousands of the same floor and roof trusses, then shipping the entire lot to site where they can be errected very quickly.

 

[KootK]

All of the truss shops that I worked for in the 90's had a special tool for field applying truss plates. It was a steel cube about the size of a cereal bowl on the end of a steel pole. You'd lay the truss against something sturdy, set the plate down, and pile drive it with the steel thingy like you were a Celtic warrior of old attempting to crush the skull of a fallen foe. I know, in retrospect, it was pretty nuts. Neither the plates nor the wood substrate fared very well in the process.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[XR250]

Seems like it would have been easier to convert a vise into some sort of field press

 

[medeek]

Most truss plants have a device for pressing plates in the field. On a large attic truss project I was involved with a number of the plates were missing on some of the webs. I alerted the truss manufacturer and the owner and they had a couple guys come out with this contraption and field installed all of the missing plates. Another thing to note was they trusses were already positioned on top of the walls at 24" o/c.

A confused student is a good student.
Nathaniel P. Wilkerson, PE

http://www.medeek.com