Roof Trusses

Question: 

I am a professional engineer looking for information concerning the failure of metal plate connected wood trusses and methods of repair. I am looking for this information with regard to developing recommendations for the repair of truss systems in the floor structures of two-story multi-family dwellings. I see frequent failure of truss systems of this type in both in bending and due to catastrophic failure at the gussets.

Question: 

What are the requirements on the permanent bracing of bottom chords? Can gypsum board diaphragms be used?

Question: 

I am a structural engineer on a project with a wood trussed roof. I have noticed some variations in the peak height in a run of identical trusses. Do you have any information on tolerances for the final dimensions of manufactured trusses?

Question: 

What type of wood is usually used for wood trusses? I live in Louisiana and I would guess pine, but I want to make sure.

Question: 

Are there any associations that have recommendations for the installation of wood trusses?

Question: 

I am a building inspector and I have a question on information provided on truss design drawings. What does the uplift reaction number represent? Some manufacturers are very specific and state “to provide for mechanical connection of the truss to the top plate with a connector capable of withstanding a specific load.” Others simply list the uplift reaction with no further information. These are the ones that have caused a debate as to what the number actually represents.

Question: 

What is truss uplift?

Question: 

I almost always see wood trusses erected with no stability bracing at points of support. It seems to me that common sense and section 3.3.3.4 of The American Wood Council’s National Design Specification for Wood Construction (NDS) require that lateral support be provided at points of bearing. Plywood decking doesn't provide any more restraint for a wood truss than it does for a roof joist. I doubt if it was a concern with short span trusses having 4 in.

Question: 

The truss industry maintains that the design of truss roof and floor system permanent bracing is the responsibility of the building designer. System permanent bracing covers the entire structure and all bracing element interactions.

Question: 

What does KD-HT mean?