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ZSJH
Custom Steel Box Girders are closed-section members fabricated from top, bottom and side plates, often with internal diaphragms and stiffeners. Their enclosed geometry provides strong torsional behavior and biaxial stiffness, making box girders suitable for eccentric loading, wide connection zones, heavy equipment support and structures where lateral stability is critical.
ZSJH Steel fabricates rectangular, trapezoidal and project-specific box girders. Internal weld sequencing, diaphragm access, plate flatness, corner geometry and closure welds are planned before assembly because much of the work becomes inaccessible after the section is closed. Access openings, drain or vent holes and sealed-zone requirements can be incorporated according to approved drawings.
Item | Available Options |
Shape | Rectangular, square, trapezoidal or custom closed section |
Plates | Top, bottom and side plates with engineered thicknesses |
Internal Parts | Diaphragms, ribs, stiffeners and connection blocks |
Connections | End plates, bolted splices, welded splices and brackets |
Access | Manholes, weld access holes, drains and vents as designed |
Welding | Internal and external welds to approved sequence and WPS |
Inspection | Dimensional checks and specified VT/UT/MT/PT |
Protection | External coating and internal treatment where required |
• Closed section offers high torsional rigidity and strong lateral stability.
• Internal diaphragms distribute concentrated loads and connection forces.
• Box width and depth can be matched to equipment or framing interfaces.
• Controlled assembly limits plate misalignment and section twist.
• Factory-installed brackets and splice details reduce site work.
• Internal preservation and sealing details can be project-specific.
Heavy industrial frames; transfer girders; equipment support beams; crane and lifting structures; large cantilevers; architectural structures; selected bridge, marine or infrastructure components subject to applicable standards.
Customization covers cross-sectional geometry, plate thickness, tapered or curved profiles where feasible, diaphragm spacing, stiffener arrangement, access holes, lifting points, splice positions, end connections, machining, sealing and internal/external coatings. Fabrication planning considers weld shrinkage and the order in which inaccessible internal welds must be completed.
1. Review internal details, weld access, closure sequence and inspection hold points.
2. CNC cut plates, diaphragms and openings with reference marks.
3. Assemble a U-shaped section using rigid fixtures.
4. Install and inspect internal diaphragms, ribs and connection blocks.
5. Fit the closing plate and weld in a balanced sequence.
6. Complete external attachments, splices and required machining.
7. Check straightness, twist, cross-section, interfaces and weld quality.
8. Clean internal/external surfaces, coat, seal, mark and pack.
Box girders are supported at engineered points to protect the closed section from local deformation. Openings and machined surfaces are covered, while internal cavities are kept dry. Oversized units can be supplied in match-marked transport segments with controlled splice geometry.
Why choose a box girder?
Its closed section provides greater torsional rigidity than a comparable open beam, which is useful under eccentric loads or where lateral stability governs.
Can internal welds be inspected before closing the box?
Yes. Internal inspection hold points can be included before the closing plate is installed.
Can large box girders be delivered in sections?
Yes. Engineered bolted or welded field splices can divide the girder into transportable segments.
Send your box girder drawings and inspection requirements for a review of internal access, welding sequence and delivery segmentation.
