Calculation of basic geometrical section properties are based on the
geometry of the section, not on stress and strain. Stress and Strain
are value which can be obtained by using geometrical section properties.
You cant calculate stress or strain without first knowing what the
section properties are can you? As for the principal axis section
properties, you can find the angle between the geometric and principal
axes using mohr's circle. Now that you know that angle, you can find
the section properties about the principal axes using the geometrical
properties about those axes.
Before you dig yourself too deep in a hole, you better dig out your old
statics book. My Beers & Johnston (3rd ed. ) in chapter 9 shows Mohr's
circle for calculating moment of inertia about any axis.
Moh's circle is not just for stress/strain!
Richard Lewis, P.E.
Missionary TECH Team
The service mission like-minded Christian organizations
may turn to for technical assistance and know-how.