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RE: truss bracing

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Andrew Kester makes very valid comments about truss bracing and the
responsibility to provide them.

However, the plated truss industry has seen fit to define the responsibility 
of the SEOR in their "standards."  In my specs/GSN I state that *all* bracing 
that is required as a condition of design be provided and detailed by the 
truss designer.

The plated truss industry states that it is the responsibility of the SEOR to 
take the bracing forces into the basic structure, however, compression 
members can be designed so they don't need to be braced or the bracing can be 
self equilibrating, e.g., X-bracing between trusses.  The bracing force 
*does not need to be taken up to the diaphragm or into the basic structure*.

I have seen long diagonal compression members bowed several inches out of 
plane.  Yes, they did have longitudinal bracing (straight 2X4's running the 
length of the roof), but the bracing was installed at the junction of the 
diagonal member and the bottom chord.  Since the location of the asterisk was 
not detailed, the builder placed the bracing where it was most convenient for 

Another place where I have seen bracing omitted is in piggyback trusses.  I 
have seen the horizontal top chord of the lower truss completely unbraced 
from end to end.  Sometimes, there will be 2X4 spacers placed between the top 
chord of the lower truss and the bottom chord of the upper truss, but that 
hardly provides lateral bracing and, of course, the plans from the truss 
designer do not detail what bracing is required.

When No. 3 grade lumber was first included in the NDS, I went to a lumber 
yard and looked at what constituted No. 3 grade.  I then went back to the NDS 
and crossed out all references to No. 3's.

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

Andrew Kester wrote:

. > In my short career I have had plenty of negative experiences with truss 
. > bracing. I think this is a very overlooked aspect of roof construction 
. > both from the engineering, constuction, and truss manufacturer 
. > standpoint. I would make sure that your notes on your plans and specs are 
. > tight and clearly dilineate responsibility, as well as show whatever 
. > typical bracing details are necessary.

. > Correct me if I am wrong here...   The two basic types of bracing are 
. > very different: bottom chord and web bracing. Bottom chord is not likely 
. > to be used except in a wind event. I have read that failure is extremely 
. > rare due to lack of bottom chord bracing but it will prevent damage. Web 
. > bracing however is needed during gravity loads if the web member is too 
. > long and it needs compression buckling bracing. This is where the truss 
. > manufacturer will sometimes skirt their responsibility, IMHO. If you have 
. > a long span with a high roof, and some of the compression members are 8+ 
. > ft long, the truss manufacturer may design the trusses in a very 
. > minimalistic way where lots of bracing is required- usually to be 
. > designed by the SE.

. > That means you have to page through the cryptic calcs to find these 
. > little marks that indicate bracing points. Then the framer has the great 
. > job of getting up there and nailing off web bracing, which needs diag. 
. > bracing back to the roof. I have seen some real messes. I believe the 
. > truss manuf. knows darn well what they are doing, and instead of just 
. > putting in a few more webs or not using #3 wood, they pass the bracing 
. > buck to the SE and GC. They get paid the same amount, and they spend a 
. > little less per truss. Sometimes they require a double web which they do 
. > not provide- the framer has to scab on braces in the field. This is 
. > ludicrous. Would Vulcraft send out joists that need extra webs and angles 
. > welded on in the field just to work?? No, they should supply a product 
. > that can withstand the loads it was designed for with minimal bracing 
. > (but why should they unless someone makes them?)

. > What I suggest , if possible, is to require that all bracing be designed 
. > and supplied by the truss manufacturer. That way you are holding their 
. > hand to the flame. They will know up front that they will not be saving 
. > themselves any time or hassle supplying minimalistic trusses. They will 
. > supply more economical trusses (for the project, maybe not them), with 
. > more webs and  them, which is way more economical for the overall project 
. > and likely to be done right then having the framer install a spider's web 
. > worth of bracing. And from their prospective, if they know what they have 
. > to do upfront, they will bid accordingly.

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