Rule of thumb is that for wood beams you do the deflection calc first,
then the strength calc since wood has a relatively low modulus of
elasticity. Steel is the opposite, you figure the strength first since
that is likely the limiting factor.


Ned: Baumeister and Marks Standard Handbook for Mechanical Engineer that I
have just about ground into unreadable by repeated usage, and I'm not a
mechanical engineer, has a table 2 on page 5-32 that shows a simply
supported beam which means the ends are only restricted vertically and not
welded into a vertical column max deflection is:


f =
(W* (5* L^3))/(384* E*I) W= weight applied to center of beam
in pounds

L= length in
inches

E= 29* 10^6 if
it is steel

I = the moment
of inertia of the I beam section. Note the way to calculate this is found
on page 5-38 of the same book. The drawing is a bit messy but the I factor
does depend on the web thickness. It is a no brainer if you have the picture
from page 5-38 and all the dimensions from the I- beam