Section properties

• Introduction
• Centre of area (centroid)
• Second moment of area (I)
• Calculating the moment of inertia (I)
• Changing to significant figures
• Comparing beam A and beam B
• Section modulus (Z)
• Calculating the section modulus
• Radius of gyration (r)
• Calculating the radius of gyration

Introduction

Section properties involve the mathematical properties of structural shapes. They are of great use in structural analysis and design. Note that these properties have nothing to do with the strength of the material, but are based solely on the shape of the section. It explains why some shapes are more efficient at supporting loads than others.

These properties are looked at in more detail following:

• centre of area (or centroid)
• second moment of area or moment of inertia (I)
• section modulus (Z)
• radius of gyration (r)

All of these values are generally calculated for both axes of symmetry (x-x and y-y on the standard coordinate plane). These axes are shown in the following diagram.