SHEAR FORCE : DEFINITION
Shearing forces are unaligned forces pushing one part of a
body in one direction, and another part the body in the
opposite direction. When the forces are aligned into each
other, they are called compression forces
William A. Nash defines shear force thus: "If a plane is
passed through a body, a force acting along this plane is
called shear force or shearing force.
Due to the act of shear force, it’s shearing, direction, and
overall analyzing of this force create a diagram that is called
the shear force diagram.
SHEAR FORCE DIAGRAM
Shear force diagram is an analytical tool used in
conjunction with structural analysis to help perform
structural design by determining the value of shear force
at a given point of an element.
The shear force diagram indicates the shear force
resisted by the beam section along the length of the
We can use a shear force diagram to analyze the beam
Using this diagram the type and size of a member of a
given material can be easily determined so that a given
set of loads can be supported without structural failure.
Although these conventions are relative and any
convention can be used if stated
explicitly, practicing engineers have adopted a
standard convention used in design practices.
The normal convention used in most engineering
applications is to label a positive shear force one
that spins an element clockwise (up on the left, and
down on the right).
The usual sign conventions to be followed for the
shear forces have been illustrated
Positive shear force
Negative shear force
GENERAL PROCEDURE TO ANALYSIS
At first, reaction forces are to be determined using
equations of equilibrium and the law of mechanics.
Shear forces are to be determined for various types of
loading case applied on beams.
According to the determined values of shear
force, the diagram is to be drawn.
Start with the far left side of the beam
2. If there is an upward force (i.e a support) then the SFD
will start at this force above the x-axis. If there is a
downward point load and no support, than the shear force
diagram will start as a negative at the value of the point
3. Move across the beam
4. As coming across the loads , by simply adding or
subtracting these loads from the value already
have, keeping a cumulative total.
Some examples of typical diagrams for various loading
cases with formulas are here .