Steel Beam Size Selector

Steel Beam Size Selector – Definition

A steel beam size selector is a structural design tool used to determine the appropriate steel beam section based on applied loads, span length, and allowable material stresses. The goal is to choose a beam with sufficient bending strength and stiffness to safely support the required loading in buildings, bridges, and industrial structures.

Background Theory

1. Bending Moment Demand

For a simply supported beam under uniform load, the maximum bending moment is:

Where:

• www = uniform load (N/mm)

• LLL = span length (mm)

This is the governing moment used for beam sizing.

2. Section Modulus (Strength Parameter)

The required elastic section modulus is:

Where:

• FyF_yFy​ = yield strength of steel

• ϕ\phiϕ = strength reduction factor

• SSS = section modulus of the beam

A beam is considered adequate when:

Section modulus represents the beam’s ability to resist bending—larger values indicate stronger beams.

3. Steel Material Strength

Typical structural steel has a yield strength of:

The calculator uses a simplified strength φ factor to approximate LRFD-style design checks.

How This Calculator Works

Step 1 — Input

The user enters:

• Span length (m)

• Uniform load (kN/m)

Step 2 — Compute Maximum Moment

The calculator computes bending moment using:

Step 3 — Compute Required Section Modulus

The tool converts units and calculates:

Step 4 — Compare With Beam Database

A built-in table of W-shapes (with Sx values) is checked from smallest to largest.
The first beam with:

is selected as the recommended beam.

Step 5 — Output

The calculator returns:

• Required section modulus

• Suggested W-shape beam

• Beam Sx capacity

This provides a quick screening tool for selecting steel beams in early-stage structural design.