Chapter-4
Bending Moment and Shear Force Diagram
S K Mondal’s
Sagging If the bending moment of
If the bending moment of
A bending moment causing
the left hand of the section
the right hand of the
concavity upwards will be
XX is clockwise then it is a
section
positive bending moment.
clockwise then it is a
called as sagging bending
positive bending moment.
moment.
XX
is
anti-
taken
as
‘positive’
and
Negative Bending Moment
Hogging If the bending moment of
A bending moment causing
the
the right hand of the
convexity upwards will be
anti-
section XX is clockwise
taken as ‘negative’ and called
positive
as hogging bending moment.
If the bending moment of the
left
section
hand XX
is
of
clockwise then it is a
then
positive bending moment.
bending moment.
it
is
a
Way to remember sign convention
x
Remember in the Cantilever beam both Shear force and BM are negative (–ive).
4.3 Relation between S.F (Vx), B.M. (Mx) & Load (w) x
dVx = -w (load) The value of the distributed load at any point in the beam is dx equal to the slope of the shear force curve. (Note that the sign of this rule may change depending on the sign convention used for the external distributed load).
x
dM x = Vx The value of the shear force at any point in the beam is equal to the slope dx of the bending moment curve.
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