I am disassembling an old potato barn for the joist timbers (doug fir) and I notice they are bowed with time. The beams are 20' in length and 3"x10" full dimension. Does anyone have ideas to take out the bow? I will try supporting them at each end with weight in the middle, but this will take some time. Maybe moisture application? They are probably 40+ years old.
(Sawing and Drying Forum)
From contributor T:
If you load it as you propose, it will probably take another 40 years. The coopers used to heat the wood under load to some 200 deg F to bend it, but I doubt that you want to do that. I have been re-sawing a large oak wine cask and, although the wood was beautiful, there were old damages from the bending that would have been important for the strength characteristics of the material if used for structural purposes.
Comment from contributor A:
If I had to guess what formula to use to predict the sag of those beams, I would choose a hyperbolic cosine (cosh). But comparing cosh (x) to a parabolic function with the same sag doesn't show any significant differences. The parabolic function has constant curvature, and hence all sections of your beams should be approximately equally deformed from straight.