I am trying to calculate the maximum torque that a piece of cypress wooden beam can handle before it snaps or becomes structurally unsound. I know this will depend on the thickness and width of the wooden beam.

Does anyone know where I can lookup the property value (coefficient or some other value) that will allow me to calculate the max tolerable torque given the thickness and width? I am looking for the value for cypress wood, but if there is a database for other types of woods, that'd be even better.

For reference, I am trying to design a bathtub bench for sitting that will hold up to 300 pounds. The current plank is 1 inch thick x 3.5 inches wide x 30 inches long.


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You can always try engineering toolbox online, it may take some digging but they would have something to give you an idea. If you are a student you can use Fusion 360 to test various materials, using the simulation environment. It is not exact, but it should have a material you can use for wood. I've used this method to calculate steel pipe strengths. Hope this helps!

The angle of twist of a wood beam in Radians is $$ θ = \frac{TL}{ GK}\space and\space torsion\space stress\space is f= T/(\beta\times h\times b^2) $$ T applied torque, L member length, G shear modulus which could be approximated by E/16, K is cross-section shape factor for a rectangular beam and beta is approximately 3 for your member dimensions, 1 and 3.5 inches.

so the stress is

$$F_{shear} = \frac {T}{\beta\times h\times b^2} $$

h is the long side and b is the short side of your member section.

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