Calculating the section modulus
To calculate the section modulus, the following formula applies:
where I = moment of inertia, y = distance from centroid to top or bottom edge of the rectangle
For symmetrical sections the value of Z is the same above or below the centroid.
For asymmetrical sections, two values are found: Z max and Z min.
To calculate the value of Z for a simple symmetrical shape such as a rectangle:
and y =
This gives the formula for Z as:
Note: The standard form of writing the value of Z is to write it as a number x 103 mm3, eg a value of 2,086 is written as 2.086 x 103.