Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

RE: truss bracing

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Title: Message
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.
 
My two Euros......
 

Andrew Kester, EI
Longwood, FL