Bending Moment Capacity

What is this formula?

The Bending Moment Capacity formula estimates the nominal flexural strength of a structural section based on the yield strength of the material and the plastic section modulus.

It is commonly used in structural steel design to determine the bending resistance of beams and other members subjected to flexure.

When to use it

Use this formula when checking the flexural capacity of steel members where plastic bending behavior is applicable and the section modulus is known.

Example

A steel beam has a yield strength of 250 MPa and a plastic section modulus of 0.0008 m³.

Data:

Fy = 250,000,000 Pa

Z = 0.0008 m³

Formula:

Mn = Fy·Z

Substitution:

Mn = 250,000,000 × 0.0008

Mn = 200,000 N·m

Result:

Mn = 200 kN·m

Applications

- Steel beam design

- Structural member capacity checks

- Plastic flexural resistance

- Building structures

- Bridge engineering

- Preliminary structural sizing

Note

This formula represents a simplified nominal plastic moment capacity. Actual design strength may require resistance factors, safety factors, lateral-torsional buckling checks, local buckling limits, load combinations, and code-specific requirements.