# RE: Principal Section Properties

• To: seaint(--nospam--at)seaint.org
• Subject: RE: Principal Section Properties
• From: Roger Turk <73527.1356(--nospam--at)compuserve.com>
• Date: Mon, 5 Apr 1999 20:41:28 -0400
```Zachery,

I faxed you a sketch of Mohr's Circle for Inertia.  Mohr's Circles can be
applied to stress, strain, and, the first one that I learned in Statics, to
Inertia.

Knowing I(z), which is the *minimum* moment of inertia for the angle and
therefore one of the properties about one of the principal axes, it turns
out that the other principal moment of inertia, the maximum moment of
inertia is I(x) + I(y) - I(z).

A. Roger Turk, P.E.(Structural)
Tucson, Arizona

Zachary Goswick wrote:

. > 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.
. >

```