**In a Nut Shell:** The
topic of shear flow frequently occurs when dealing with “built-up”
beams. These are beams fabricated with
several pieces joined by glue, nails, bolts, or
welds. These fasteners must be
sufficiently strong to withstand the lateral (transverse)
or longitudinal shear. It is common to
describe the load by the term, “shear flow” given
by the following relation:
where q is the shear flow in (lb/in), (lb/ft), (N/mm), (N/m)
V is the value of the shear
force at the section
Q is the first
moment of the area between the location where the shear stress
is being
calculated and the location where the shear stress is zero about
the neutral (centroidal)
axis; Click here for discussion
of Q.
I is the moment of inertia of the entire
cross-section about the neutral axis
The shear flow may be used to calculate the shear stress (in the case of continuous
joints)
by dividing by the width of the beam supporting the stress.
where t
is the width of the cross-section at the location where the shear
stress is
being
calculated
If the joints are not continuous such as in nails, screws, and bolts, then it
is more convenient
to
use q
as force per unit length along the beam.
In
such a case q (lb/in) =
F(lb/nail) / s(in/nail)
Here F
= s q and
F is the force across one nail
and s is
the nail spacing.
Click
here for strategy in calculating shear flow in beams. Click here for examples.
** ** |