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RE: Question on wood Roof Trusses

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Peter,

At the risk of being flamed, I will repeat, "There is *no need* to carry 
bracing forces down to the base structure!  This is a condition of design and 
can be self-equilibrated."

The designer of a pony truss bridge does not carry the compression chord 
bracing forces to the abutment.

The designer of a thru truss bridge does not carry the compression member 
bracing forces to the abutment.

The internal bracing of compression members does not cause the structure 
reactions to change as there are no new external forces involved.

Likewise, the designers of metal plate connected wood trusses can provide 
the necessary bracing of compression members without carrying the forces down 
to the base structure.

A. Roger Turk, P.E.(Structural)
Tucson, Arizona

Peter McCormack wrote:

>>Sorry if this is a repeat message, but I have been very busy the 
last couple of days and only gave my emails a cursive glance....to 
my dismay....

Dennis...can you summarize the thread for me? Where do we 
stand (the building designer) are we responsible for the bracing, 
connections etc of the truss system, or is this the responsibility of 
the truss designer (who I had been assuming was responsible)

The little truss diagrams I have seen specify the reactions at the 
heal of the truss, the assumed loading, but little information on 
laterial loading. For example, if I am responsible for the lateral 
bracing, how do I effectively design a bracing system without 
knowing if the "cladding and component" pressures I apply to the 
webs of a gable truss is the same as the truss designer to 
determine if I need to strengthen the webs with 'L' bracing or if the 
vertical diagonal bracing up to the top chord of an internal truss 
(and another to the bottom) will be adequate.

As for the location and connections of bracing to prevent the out of 
plane buckling of the truss chords etc....do I need to analyze the 
system myself? What about the load-slip parameters of the metal 
plate connections?

This is scary.....<<