As was stated before, it is not sag you need to worry about but
load capacity. Wood is pretty flexible so in a building you
ususally run up against the sag issues before the load
considerations. Here it is all about load. And load issues tend
to be catastrophic.

All the lumber is sized for house building things done in a
'standard' fashion. You are using it completely differently.

There is a beam loading calculator that some of the NG guys use
(I have a different one), see if someone will give a URL for it.

Use these values for a 2x4 laid flat:
Section Modulus = 1.3125
Moment of inertia =
Fb (max stress) = 900 psi (pretty variable!)
Youngs Modulus (elasticity) =1,000,000

Cheers.

Loren Coe wrote:

In article , Fitch R Williams wrote:

Loren Coe wrote:


with support at 32" intervals, how much load can a 2x4
support on its side?

btw, i am using 5/16"x3" lag bolts to fasten the brackets.

You might give some thought to the total load and moment on the studs
you are fastening this monster shelf to. It might be that the wall is
the weakest part of this structural system. Fitch


i hope the hell not. i possibly overstated the intended load, that one
33-34" section was pretty much the max, and not typical. the 40" section
was probably unique, against a plumbing wall, which actually speaks to
your point. those walls are pretty chopped up and even tho 2x the width,
are a worry. hopefully, i will hear some kind of creak or groan before it
completely collapses. :-(

there will be only a single shelf of the type i have described, but
definitely made to take a load. if i can relate the "sag" data to
some "limit" data, that would be useful. otherwise i plan to keep
an eye on things and an ear open. escpecially since another poster
cautioned the same as you. Best Regards, --Loren

ps. aren't you going to miss the Great NW? a brother and grandfather
both worked for Boing, the So. Seattle plant.