On Wed, 13 Feb 2013 08:10:49 -0500, "dadiOH"
wrote:

Jim Elbrecht wrote:
Darro wrote:

The plan is to construct the beam with two rows of 2x3 spruce or
hemlock lengths with their sides bolted together to make up a beam
that is 2-1/2 inches in the vertical dimension and 3" in the
horizontal.

The total load on the beam would be about 30lbs. and would be
distributed evenly along the full length of the beam.

I say it can't be done.

Yes it can.

There is a span calculator someplace on
the web. It has been posted here. See what they say you can build
a 12' span with.

They say, using hemlock, that the sag would be 0.009" per foot, 0.11" total.
Increasing the load 10X would increase the sag approximately 10X too.
http://www.woodbin.com/calcs/sagulator.htm


Using Eastern Hemlock, I confirm about 1/2 " total compared to my
earlier manual calculation. Remember to use floating ends
(conservative) and don't forget to include dead load with live load.