top chords bowing from stress
top chords bowing from stress
(OP)
I am hanging 60'- 3" gable trusses(4/12)and my top chords are bowing(and racking)in opposite directions(uniformly) on all my installed trusses. They are literally trying to lay down on the headers. One side toward the front of the building, the other toward the rear. When I try to plumb and lathe the top chords on one side, it aggravates the bow in the other side in an extreme(and scary)way. The builder I worked for prior to starting my own company inspected my build to try and help me dtermine the cause of this problem. The only thing he could come up with was that this truss behavior is due to the rafter lengths being too long and causing compression stress. He was right, they are too long. We measured them this afternoon. The bottom chord is built to the precise measurements shown on the spec sheet, but the top chords are not. Most are a combined total of 3/4"(or more)longer than the design drawing calls for. Could this be causing enough compression stress to force the trusses to behave like this? This is the second time I have attempted to hang them. This is a dangerous situation for my crew. Any help would be appreciated.





RE: top chords bowing from stress
Let me say this , If you are setting a 60-0 + span truss, you will have to go to extra efforts in order to keep them plumb. Can you say extra bracing???
JP
Truss Designer
RE: top chords bowing from stress
RE: top chords bowing from stress
RE: top chords bowing from stress
The truss supplier should have supplied you with literature on the correct method of installation (or where to obtain it).
Goto WoodTruss.com and read the free technical sheets:
-Installation of Long-Span trusses
-Temporary (during construction) bracing
-Permanent Bracing
The building designer should make sure the top chords are adequately braced with the purlins and metal roof diaphragm.
Too many of these trusses end up on the ground.
I'm sure the fabricator will provide the literature when he sells you the second set (replacement) trusses.
RE: top chords bowing from stress
RE: top chords bowing from stress
Of course if you bought the trusses from a legit company you should complain that they arent built to spec if the top cords are too long.
RE: top chords bowing from stress
My initial guess is going to be that the only bracing is the purlins themselves and they are all perpendicular(sp?)to the trusses themselves. Is this true? If so youll need to apply some "X" bracing or "45 degree" style bracing.
Check this TPC info out
http://ww
One other question I have is were the trusses plumb when they were istalled? Im sure if you asked the framer he will say he did. What kind of bracing is on the bottom chords?
One other thing is what is the truss spacing and loading? I would make a check on that also.
What style bracing is being used at the gable ends? Is there a diagonal brace from the bottom chord going back into the truss system?
Best of luck... JP
JP
Truss Designer
RE: top chords bowing from stress
Not the tpc.... thats a golf club.
JP
Truss Designer
RE: top chords bowing from stress
RE: top chords bowing from stress
RE: top chords bowing from stress