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Q: Beam Sizing - Construction design question ( Answered,   1 Comment )
Subject: Beam Sizing - Construction design question
Category: Science
Asked by: drdestructo-ga
List Price: $20.00
Posted: 26 Aug 2006 08:47 PDT
Expires: 25 Sep 2006 08:47 PDT
Question ID: 759713
I am planning on building a loft in my shop.  It will be used for
storage of "normal" weight items (nothing extraordinary).  It will be
against the back wall of my shop and I can attach a ledger board to
that wall.

The deck will be 24 feet wide and will extend 8 feet out from the
wall.  I would like to span all 24 feet at the front from the two
front corners.  I am trying to figure how big of a beam will I need to
support this size span.  I intend to weld up brackets, placed on wood
or steel posts, for the corners to support the beam.  I could have a
center post, but would really prefer not.  Anything up to 4x18 or 6x18
is doable.

I plan to deck this with 3/4 plywood on top of 2x8 joists, 16" oc,
spanning the 8 feet.

The question:  Size a glulam beam spanning 24 feet.  Size one more for
if the span increased to 26'.  Can this be supported on 6x6 or 8x8
wood posts?
Subject: Re: Beam Sizing - Construction design question
Answered By: redhoss-ga on 26 Aug 2006 10:03 PDT
Hello drdestructo, I recently downloaded span tables from:

The one that applies to your question is "TABLE DF30" for floor loads
using Douglas fir-Larch glulam beams.

Before entering the tables we need to know the applied load in pounds
per lineal foot (plf). In your case I think we could safely use a dead
load of 10 psf and a live load of 60 psf. This gives us a total load
of 70 psf. Since your span away from the wall ledger is 8' the beam
will support 4' of the load. So, 4 ft x 70 lb per sq ft = 280 plf.
From the tables:

24 ft span:
Looks like your choice would be a 3 1/2 x 16 1/2 or
                                  5 1/2 x 15     or
                                  6 3/4 x 13 1/2

26 ft span:
Looks like your choice would be a 3 1/2 x 18  or
                                  5 1/2 x 15  or
                                  6 3/4 x 15

The load supported by each column in the 26' span case would be:

P = 280 x 26 / 2 = 3,640#

On a 6 x 6 column this would be 3640/(6 x 6) = 101 psi. There is
certainly no problem with compressive strength. I would suggest
fastening the column to the wall at mid-point (you don't say how tall
the columns would be). This would give you some additional safety in
case something damages the column and remove any chance of failure due
to buckling.

Please ask for a clarification if there is any of this you don't understand.

Good luck with your project, Redhoss
Subject: Re: Beam Sizing - Construction design question
From: garysouth-ga on 11 Sep 2006 10:03 PDT
I was looking for information on span tables myself since I face a
similar situation. Unfortunately the address given in the reply does
not provide those span tables. If any other span tables are available.
my load calculations came out to be a total of 13000 # on a 20 foot

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