Design of arched bottom chord of timber truss
Design of arched bottom chord of timber truss
(OP)
I am working on the design of a heavy timber truss with an arched bottom chord (30' radius). The architect would like to cut the bottom chord from a 8x18 or 8x20 to be an 8x14. The chords will be spliced at the center king post. Is this even possible? Or does it need to be glulam?
The loads in the bottom chord are as follows:
Tension = 9.0 kips
Moment = 9.0 ft-k
I calculated my radial tension per NDS 5.4.1.3: fr = 3M/2Rbd = 3*12000*9.0/(2*30*12*7.5*13.5) = 4.44 psi <= 15 psi.
Is this correct?
Any ideas on how I can check a solid sawn member?
Thanks!
The loads in the bottom chord are as follows:
Tension = 9.0 kips
Moment = 9.0 ft-k
I calculated my radial tension per NDS 5.4.1.3: fr = 3M/2Rbd = 3*12000*9.0/(2*30*12*7.5*13.5) = 4.44 psi <= 15 psi.
Is this correct?
Any ideas on how I can check a solid sawn member?
Thanks!






RE: Design of arched bottom chord of timber truss
Whatever you do, don't forget to account for the thrust caused by the arch.
RE: Design of arched bottom chord of timber truss
Just out of curiosity, I did a rough check to see if the geometry of cutting a curved (rough) 8 x 14 out of a (rough) 8 x 20 would yield a significant length curved 8 x 14 beam. Assuming the ends of the curved 8 x 14 are perpendicular to the beam's center line, I get a length of less than 12'. You did not mention the required length, but sounds somewhat short.
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RE: Design of arched bottom chord of timber truss
RE: Design of arched bottom chord of timber truss
RE: Design of arched bottom chord of timber truss
RE: Design of arched bottom chord of timber truss
I quite agree. One thing that I've always struggled with, however, is how far to take my own investigation of such a delegated item before passing it on. Obviously, not just anything will work, particularly when it comes to connections. Got any advice in that regard? All that I've heard so far is that keeping your member utilization under 70% might facilitate doable connections. Rough science.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Design of arched bottom chord of timber truss
RE: Design of arched bottom chord of timber truss