128
,. , «1 S'] are
respectively above and below
axis in unsymmetrical figures.
SECTIONS.
INEBTIA AREAS.
MOLESWORTHS J/OCKET-ßoOK
Moment of Inebtia. (Graphic Construction.)
D = Distance of edge of section from neutral axis
■ g - Distance of centre of gravity of each section
ot the “ inertia area ” from the neutral
axis.
a = Section of “inertia area” above or below
neutral axis.
1 = Moment of inertia = 2 D a g- in symmetrical
ngures.
I D a g + D] ax gx, where D a g and D.
dimensions __ ’
the neutral
To form the “in-
ertia area ” divide
the section into any
convenient layers,
drawing horizontal
lines to represent the
layers and neutral
axis. On a horizon-
tal line distant D
from the neutral axis
set off from any ver-
tical line represent-
ing the widths of
each layer respec-
tively, and from the
widths thus set off
draw lines radiating
to the point of in-
tersection of the ver-
tical line with the
neutral axis, then
the intersection of
these radiating lines
with the respective
horizontal lines of
each layer will give
points in the line
which limits the
“ inertia area.”