Truss Bracing
Truss Bracing
(OP)
I am in the middle of designing exposed Glulam trusses. These trusses are parallel chord flat trusses about 7'-6" in depth, and are top chord bearing. The bottom chord is entirely in tension, and I am trying to determine if and how to brace the bottom chord. The trusses will span 66' and the bottom chord is about 55' feet long, and the truss overall looks very similar to a steel bar joist, at least in shape. The 1997 NDS (ASD) Appendix A (A.10 part B) says 'Also bottom chord lateral bracing should be installed in the same bays as the vertical sway bracing, where practical (I hate that phrase), and should extend from side wall to side wall.' I cannot picture what this sentence is telling me to do, this bracing is different than the struts between bottom chords which should extend from 'end wall to end wall' which I can picture. Can anyone explain this sentence to me, and can anyone provide any experience in the bracing situation I have as a whole?






RE: Truss Bracing
RE: Truss Bracing
RE: Truss Bracing
However the "where practical" as you indicate leaves the thing loose, since many won't want what to them may look unnecessary, once all is properly accounted for.
RE: Truss Bracing
RE: Truss Bracing
RE: Truss Bracing
Your trusses are large and any out-of-plane load may fail the trusses so the answer to your simpler question 'if' to brace the bottom chord is a definite yes.
Since the spacing of the trusses is also large at 24', I feel, it will not be possible to use single members as tie rods between the bottom chords due to slenderness difficulties. You need another trusses from each vertical of the left-truss to corresponding vertical member of the right-truss to take care of lateral loads.
Weld perpendicular gusset plates to each gusset plate at ends of each vertical member. You can then use these perpendicular plates to connect your lateral trusses. In the end you will have a grid like pattern of trusses in plan view. Remember to stiffen the right angle between the gusset plates.
HTH
RE: Truss Bracing