Free Steel Plate Girder Calculator — Design Guide
Design built-up steel plate girders for heavy loads and long spans. The calculator checks flexural capacity of slender-web girders, shear buckling with tension field action, intermediate and bearing stiffener design, flange-to-web weld requirements, and combined flexure-plus-shear interaction per AISC 360-22 Sections F5 and G2-G3, AS 4100 Section 5, EN 1993-1-5, and CSA S16 Section 14.
Applications: bridge girders spanning 80-200+ ft, heavy industrial crane girders, transfer girders in buildings, and long-span roof girders. Plate girders are economical when standard rolled W-shapes are inadequate.
How to Use
- Enter girder geometry: overall depth, flange width and thickness, web depth and thickness.
- Select material: flange and web grades (typically A572 Gr 50 flanges, A36 web).
- Define loading and bracing: uniform or concentrated loads, lateral bracing of compression flange.
- Review flexure: compact/noncompact/slender classification, composite vs non-composite.
- Check shear: web buckling (h/tw), tension field action, stiffener spacing.
- Design stiffeners: bearing stiffeners at supports, intermediate transverse stiffeners.
Design Code Requirements
| Check | AISC 360 | AS 4100 | EN 1993-1-5 | CSA S16 |
|---|---|---|---|---|
| Web slenderness limits | F5.2 (h/tw ≤ 5.7√(E/Fy)) | Cl 5.2.2 | Cl 5.1 | Cl 14.2 |
| Flange compactness | B4.1b (bf/2tf limits) | Cl 5.2 | Cl 5.3 | Cl 11.2 |
| Flexural strength (slender) | F5.3-F5.6 | Cl 5.3 | Cl 5.4 | Cl 14.1 |
| Shear (web buckling) | G2.1 (Cv factor) | Cl 5.11 | Cl 5.2 | Cl 14.4 |
| Tension field action | G3 | Cl 5.11.3 | Cl 5.3 | Cl 14.5 |
| Transverse stiffeners | G2.2 | Cl 5.12 | Cl 5.4 | Cl 14.6 |
| Bearing stiffeners | J10.8 | Cl 5.13 | Cl 6.2.6 | Cl 14.7 |
Key Design Considerations
- Flange proportioning: Flange area Af ≈ Mu / (phi _ Fy _ d * 0.95) for preliminary sizing
- Web proportioning: Web depth h ≈ L/12 to L/15 for economical designs
- Optimal span-to-depth range: 12-20 for plate girders
- Web slenderness: h/tw typically 150-300 for optimized girders
- Tension field action: Only available when transverse stiffeners are provided (a/h ≤ 3.0)
Frequently Asked Questions
What is the economic span range for plate girders vs rolled sections? Plate girders become economical when spans exceed 60-80 feet and standard W-shapes are insufficient or when the required section is deeper than 40 inches. Between 40-60 feet, assess both options — a deep W-shape (W40 or W44) may be more economical than a built-up plate girder due to lower fabrication cost.
What is tension field action in plate girders? Tension field action is the post-buckling shear resistance in slender webs. After the web buckles in shear, diagonal tension develops along the web's tension direction, anchored by transverse stiffeners and flanges. AISC 360-22 Section G3 provides the tension field action equations. This mechanism provides 30-60% additional shear capacity beyond elastic buckling and is available only when stiffener spacing a/h ≤ 3.0.
When are transverse and bearing stiffeners required? Transverse (intermediate) stiffeners are required when the nominal shear strength without tension field action is inadequate or when a/h > 3.0. Bearing stiffeners are required at supports and concentrated loads where web yielding or crippling governs. AISC 360-22 Section J10.8 provides the design procedure for bearing stiffeners — they must be designed as compression members with an effective column section including a portion of the web.
Which design standards cover plate girders? AISC 360-22 Sections F5 and G2-G3 in the US, AS 4100 Section 5 in Australia, EN 1993-1-5 (plated structures) in Europe, and CSA S16 Section 14 in Canada.
Is this plate girder calculator free? Yes, completely free with unlimited calculations.
Disclaimer (educational use only)
This page is provided for general technical information and educational use only. It does not constitute professional engineering advice. All structural designs must be verified by a licensed Professional Engineer (PE) or Structural Engineer (SE). The site operator disclaims liability for any loss or damage arising from the use of this page.