Wood Truss Plates ??? 1

[sgc]

Greetings,
I am kinda new at this site so forgive me if I have this entered more than once.
I want to beef up the load handling ability of some existing 2" x 4" syp trusses which are constructed with small metal plates. I would like to cut larger (much larger than the metal plates) pieces of plywood and glue and attach these new oversized wood truss plates over the existing metal plates.
Is liquid nails the best glue to use?
Can I use a staple gun or is nails the best choice? What length?
Will 1/4" plywood be the best thickness plywood to use?
I considered getting larger metal plates with predrilled holes but the cost gets way high for say 12" or larger plates, then I would have to hand nail these plates to boot.
Any advise welcomed.
Thanks,
SGC

 

[sc]

sgc

Glue only is not a means of creating good quality fixity of the gussets to timber trusses. The reason being that glue only holds to the surface of the timber, thus creating a shear connection on a very small thickness. In some cases timber will shear before the glue.

Staples do not have a good shear strength or pull out strength (that is why truss manufacturers use nail plates). The Australian timber codes recommend nailing or screwing at fairly close intervals for ply gussets.


I don't know if I missed it in the earlier posts, but you will also need to consider the additional live loads. If the attic created is to be used for storage then there will be minimum live loads that are significantly more than normal floor live loads (it will be in the loading code somewhere).

Please keep chasing your PE for the answer.

regards
sc

 

[Miper]

Wood airplanes were and are glued together, and trusses are extensively used in wood airplanes. The joints are gusseted and the gussets are usually attached with glue only, no nails or staples. A good glue joint will always hold while the adjacent wood fails. That is the definition of a good joint, not a bad joint -- provided that the joint is primarily in shear and not in bending. If you have large bending loads within the joint, then a glue failure could result from shear at the surface, but the whole point of a truss design is to have essentially no appreciable moments transferred across the joints.

In airplane structures, nails are not used because they tear up the wood badly and because they tend to pull out, while glue has none of these drawbacks.

I know, I know, this isn't an airplane, but to say that a nailed joint is better than a glued one makes no sense to me.

Perhaps the Australian code requires closely spaced fasteners in ply gussets because of the inherent weaknesses of building grades of plywood, which have lower strength than solid wood and a tendency to delaminate.

 

[sgc]

Gretings again,
It is good to hear different peoples views and coming from different backgrounds makes for interesting perspectives.
I am getting a little concerned about my PE, I am not sure if he is too busy or didn't take this little home project of mine serious.
There is a wall inside the building that I could convert to load bearing. I could use this wall and the two end walls as support, go into the attic and place beams directly under the peak where the load is greatest. But this will give me a 30' span to deal with. Getting the beams in there is possible through the end walls, but the question is the design of the beams. I recently went into a local house being built and they had 3 - 16" laminated type beams nailed together with a 30' span to hold up the second floor and roof. I am wondering about this possible approach to my situation.
I do appreciate the responces and any expertise in these areas.
SGC

 

[smcadman]

I found this site when I was searching for trusses for a 10' x 12' mini-barn (shed with gambrel-roof) that I am building:

http://www.truss-frame.com/

I hope it helps a little.

Flores

 

[smcadman]

Oops, the "I" was attached to the link. Here it is again:

http://www.truss-frame.com/

Flores

 

[wishinew]

Let's say your Architect knows what he is saying. The following info I used when I built my own trusses. From the book "Basic Carpentry" by John Capotosto, copywrite 1975, Page 200. You can use 3/8" or 1/2" exterior grade plywood, waterproof glue, 4d (3/8"ply) or 6d (1/2" ply), 3" on center. A picture of this truss was donated by the "Forest Products Lab." Look it over before you act.

 

[sgc]

Greetings Again!
I gave up on my PE (still hasn't gotten back to me). I have been working with an architect who is one of the two designers on a multi million dollar building project under way where I work. I asked this architect if he would help me with my home project plan, to my delight he took it seriously and drew it up and made the following observations. The additional weight was not the problem (as coferred by the PE I was previously going to use) but the moments were of concern. The structural recommendation was to nail 45 degree knee bracing 4' lateral and 4' vertical connecting each top truss and the side walls (just under 4' high) (trusses are on 16" centers). Also being the non-risk person that I am, and taking the advice of this thread's expertise, I am planning to adapt a few non-load bearing walls to load bearing and will be installing some beam support to boot.
Wishinew and Smcadman I appreciate the imput and am interested in the sources you submitted.
Thanks again,
SGC