A structural steel welded box beam is a high-performance member fabricated from four steel plates into a closed, rectangular section, giving extreme torsional rigidity and balanced strength in both axes. Because the closed profile forms a continuous load path around its perimeter, its torsional stiffness is 50–100 times that of an equivalent open section and it resists lateral-torsional buckling inherently, so engineers can span further and design taller, more slender frames under heavy and eccentric loads.
We fabricate box beams and columns from Q235B/Q355B, S235JR/S355JR or A36/A572 Gr.50, with internal diaphragms at the spacing your load demands and corner seams by SAW under WPS/PQR. Members are Tekla-detailed, dimension-checked, critical welds UT/RT Grade I/II, then Sa2.5 shot-blasted and painted or galvanized.
Specification of Box Beams
| Product | Welded steel box beam / box column (four-plate closed rectangular section) |
| Section Type | Closed box, welded from four plates; internal diaphragm stiffeners as required |
| Material | Q235B/Q355B · S235JR/S355JR · A36/A572 Gr.50 |
| Dimensions | Plate width/thickness sized to section modulus; length per transport or in segments |
| Welding | SAW corner seams under WPS/PQR; internal diaphragm seams pre-completed |
| Welding Grade | I/II (UT/RT on critical & full-penetration welds) |
| Surface Treatment | Sa2.5 + high-performance painting · hot-dip galvanizing |
| Connection | High-strength bolted splices or site welds; end plates as required |
| Detailing | Tekla Structures (BIM) + shop/assembly drawings |
Why This Welded Box Beam?
Extreme torsional rigidity - closed loop carries torque around the perimeter, resisting twist that fails an open section.
Balanced biaxial strength - equal two-axis stiffness suits two-way bending and slender high-rise members.
Resists lateral-torsional buckling - stable under heavy eccentric loads, longer spans without extra bracing.
Internal diaphragms & local stability - ratios and spacing set to your load to prevent plate buckling.
SAW + WPS/PQR weld quality - corner seams SAW, critical welds UT/RT Grade I/II.
Tekla detailed & erection ready - BIM-accurate with drawings and optional third-party inspection.
Applications of Box Beams
Bridge Engineering - main load-bearing girders for long-span bridges and elevated highways, where high torsional rigidity controls eccentric traffic/wind loads.
Heavy-Duty Crane Runway Beams - runway beams for high-capacity overhead cranes in steel mills and heavy manufacturing, resisting dynamic lateral loads and sway.
Large-Span Public Buildings - wide clear-span roof frames and transfer structures in airports and stadiums.
High-Rise Construction - primary horizontal members, transfer girders and corner columns in skyscrapers.
Heavy Equipment Support & Machinery - support frames for crushers, screens and power-plant boilers on mining and energy platforms.
Our Customization Service
What We Can Customize
Section geometry (plate width, depth, thickness sized to section modulus and torques).
Internal stiffeners (diaphragm spacing, full/partial depth per local stability).
Steel grade (Q235B/Q355B, S235/S355, A36/A572 Gr.50, higher on request).
Connections (end plates, bolted splices, site welds).
Coating (Sa2.5 + paint or hot-dip galvanizing).
How Customization Works
Send section modulus, span, torques and connection requirements.
Engineer proposes plate sizes, diaphragms and quotation.
Shop/assembly drawings for approval.
Plate cutting, SAW welding, NDT, coating and QC.
Whole or segmented dispatch with MTC and documents.
Packing & Delivery of Box Beams
| Item | Detail |
|---|---|
| Packing | Anti-rust film; edges and coated faces padded. |
| Lifting | Spreader-beam/sling lifting to prevent bending and torsion. |
| Segmentation | Long members whole or in matched segments with splice hardware + details. |
| Transport | Sea-worthy on heavy skids/container cradles, strapped; FOB/CFR/CIF. |
| Docs shipped | Packing list, invoice, MTC, welding/NDT, coating, dimensional report, shop/assembly drawings. |
FAQ:
Why choose a box beam over an open H/I-section of the same weight?
A closed box loops loads around the perimeter - torsional stiffness typically 50–100× an open H - with balanced biaxial strength, letting you design taller, slimmer frames without lateral-torsional buckling for long spans, curved members and torsionally loaded elements.
What section dimensions and steel grades can you fabricate?
Any length transport allows; web/flange widths and thicknesses sized to section modulus with internal diaphragms as needed; grades Q235B/Q355B, S235JR/S355JR, A36/A572 Gr.50, high-strength on request.
How are the four plates joined and how is weld quality assured?
Corner seams by SAW under WPS/PQR with diaphragms first; critical and full-penetration welds UT/RT Grade I/II and corner fillets inspected.
Do you provide engineering design and drawings?
Yes - Tekla (BIM) detailing, shop/assembly drawings, checked to GB 50017, EN 1993-1-1 or AISC 360; diaphragm spacing and ratio/buckling curves set to load.
Do you supply traceability and third-party inspection?
Yes - MTC, welding/NDT (UT/RT), coating records and dimensional results; SGS / BV / TÜV third-party inspection on request.
