Redwood beam span and also the “golden mean”
yojimbo2
| Posted in General Discussion on
I am going to build a pergola. The front beam has to span 17′. It will have approximately 18, 4×6 at 12′ redwood sitting on it. The other ends of these redwood 4×6 will be attached to a ledger on the house. I have been unable to find a span table for anything like this.
I was thinking of using an 8×10 redwood beam to span this distance. Too big, too little, any thoughts.
Another thing I have been grappling is the ideal height of a pergola. It will be covering an outdoor kitchen. I was leaning towards 8′ to the bottom of the lowest member. I would like to use the “golden mean” to figure this out, but I have no idea how to do this.
Replies
I would prefer a 6x12 beam, but that one you have will do it fine. Remember this is only supporting dead load since a pergola supports no live loads, unless you grow a massive grape arbour over it as well.
i'm not sure how to apply the golden rectangle ratios to height of a 3D space, only 2D opennings
I would like to use the "golden mean" to figure this out, but I have no idea how to do this.
Scale it to the dimensions of the Parthenon.
The golden ratio = 1.61803399
The golden ratio = 1.6180339. So for a 17' long section, the height would be 10' 6".
Pergola beam span
Actually a 4x10 with an Fb 1300 and an E 1,100,000 will be more than enough to do what you describe. Beyond that it is whatever look you want.
The attachment to the house and rigidity also needs to be adequately addressed.
Actually a 4x10 with an Fb 1300 and an E 1,100,000 will be more than enough to do what you describe
I think I know what the E stands for-modulus of elasticity, but not really sure how to use that information.
I looked up Fb -Fb (F sub b) is an engineering symbol for the bending strain, in P.S.I. of a beam. F sub b = M(Y)/I
again, not sure how to use this.
Is there an online beam span table available? I have only been able to locate one for joists.
Agree with 4x10
One question...will the 4x6's spaced 12" on center look too heavy?
It depends -- is it your wife asking?