Formula used
The calculator first evaluates yielding and local buckling. It then checks lateral stability using entered restraints. The smallest resistance controls the reported beam capacity.
How to use
- Select the design standard and reporting method.
- Choose units, steel grade, and section shape.
- Enter geometry or provide trusted section properties.
- Define span, unbraced length, supports, and restraints.
- Select a load case and enter design actions.
- Enable shear and interaction checks when required.
- Calculate and review every governing engineering warning.
Example data
| Example | Section | Steel | Span | Unbraced length | Load case |
|---|---|---|---|---|---|
| Fully braced beam | Wide flange | S355 | 6,000 mm | 500 mm | 35 kN/m UDL |
| Unbraced beam | Wide flange | A992 | 24 ft | 12 ft | 2.2 kip/ft UDL |
| Cantilever beam | RHS | S275 | 3,000 mm | 3,000 mm | 45 kN point load |
| Plate girder | Built-up I | S355 | 12,000 mm | 4,000 mm | 90 kN/m UDL |
Assumptions and limitations
This tool provides an engineering screening calculation. It uses simplified code-based stability relationships. Final designs require complete code verification and detailing.
Automatic geometry supports common symmetric steel sections. Channels and built-up shapes need verified manual properties. Connection resistance and serviceability remain separate checks.
Loads should already include required combinations and factors. Local rules may change resistance factors. A qualified structural engineer must approve final construction documents.
Frequently asked questions
What is steel beam moment capacity?
Moment capacity is the beam’s available bending resistance. It depends on strength, shape, and restraints. The lowest applicable limit state controls final capacity.
Why does unbraced length reduce capacity?
Long compression flanges can move sideways and twist. This behaviour causes lateral-torsional buckling. Additional bracing usually increases available bending resistance significantly.
What is a compact steel section?
A compact section can develop plastic resistance before buckling. Its elements remain within code slenderness limits. Compact sections usually provide the highest practical bending capacity.
Should I use plastic or elastic modulus?
Plastic modulus supports plastic moment calculations. Elastic modulus identifies first yield resistance. The selected design standard determines the permitted method.
What does Cb represent?
Cb adjusts resistance for the moment gradient. Nonuniform moments can improve lateral stability. Use a code-compliant value for the actual loading.
When does shear reduce bending capacity?
High web shear changes the available bending resistance. Codes provide interaction or reduction rules. This calculator applies a simplified high-shear reduction check.
Can hollow sections experience lateral buckling?
Closed sections have strong torsional stiffness. Lateral buckling often becomes less critical. Local wall slenderness may still control capacity.
Why enter manual section properties?
Manufacturer tables provide accurate properties for rolled sections. Built-up sections need verified calculations. Manual values also support shapes outside automatic geometry.
Can this replace structural design review?
No calculator captures every project requirement. Connections, deflection, fatigue, fire, and stability need review. Engage a qualified engineer before construction or procurement.