From: nicksanspam@ece.villanova.edu
Newsgroups: alt.building.construction alt.home.repair misc.consumers.house misc.rural
Subject: Re: Maximum Span for Shed, without supporting posts??
Date: 28 May 2005 08:30:20 -0400

James  wrote:

>...how far can you span with 2 x  10's, and how far with  2 x 12's  ?
>By the way, these joists were 12 inches apart.

If modulus S = bd^2/6 = d^2/4 in^3 for b = 1.5" and bending moment M = Sf
= 250d^2 in-lb for fiber stress f = 1000 psi and total load W = 8M/(12L)
= 167d^2/L pounds for an L' span, floor loading w = W/(LC) = 167d^2/(L^2C)
pounds per square foot (psf) for L' beams on C foot centers.

So 9.25" 16' 2x10s on 1' centers might support w = 167x9.25^2/(16^2x1)
= 55.7 psf. On 16" (1.33') centers, w = 42 psf... 11.25" 2x12s with
L = 24' make w = 167x11.25^2/(24^2x1.33) = 27.5 psf, with cross-bracing
for torsional longitudinal stability.

With a post and beam in the middle to halve the span, 12' 2x10s on
2' centers might support w = 167x9.25^2/(12^2x2) = 50 psf... 2x8s
might do w = 167x7.25^2/(12^2x2) = 30 psf.

Nick