Elastic Section Modulus
For general design, the elastic section modulus is used, applying up to the yield point for most metals and other common materials.
The elastic section modulus is defined as S = I / y, where I is the second moment of area (or moment of inertia) and y is the distance from the neutral axis to any given fibre. It is often reported using y = c, where c is the distance from the neutral axis to the most extreme fibre, as seen in the table below. It is also often used to determine the yield moment (My) such that My = S × σy, where σy is the yield strength of the material.
| Cross-sectional shape | Figure | Equation | Comment |
|---|---|---|---|
| Rectangle | Solid arrow represents neutral axis | ||
| doubly symmetric I-section (strong axis) | NA indicates neutral axis | ||
| doubly symmetric I-section (weak axis) | NA indicates neutral axis | ||
| Circle | Solid arrow represents neutral axis | ||
| Circular tube | Solid arrow represents neutral axis | ||
| Rectangular tube | NA indicates neutral axis | ||
| Diamond | NA indicates neutral axis | ||
| C-channel | NA indicates neutral axis |
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