Steel Box Girder Bridge Fabrication per AASHTO, AS 5100 & Eurocode Standards

A steel box girder bridge is a type of bridge that uses a closed box-shaped section as the main girder, composed of a top plate, bottom plate, webs, and stiffeners to form an integral load-bearing structure. Due to its superior torsional stiffness, lightweight self-weight, and prefabrication features, it is widely used in long-span highway bridges, urban viaducts, rail transit, and curved bridge projects, making it one of the mainstream forms of modern steel bridges.

1.Application Scenario

2.Product Highlights

ü Excellent torsional stiffness: The torsional stiffness of closed sections is hundreds of times higher than that of open sections, making it particularly suitable for curved bridges and eccentric loads.

ü Low building height: Under the same span, the beam height of steel box girders can be reduced by 30%–40% compared to concrete beams, which is convenient to meet the headroom limit under the bridge.

ü Factory prefabrication: the segments are cut, welded and painted in the workshop, and only need to be assembled and welded with ring seams on site, and the quality is stable and controllable.

ü Light weight: Compared with concrete box girders, the dead weight is reduced by 50%-60%, and the cost of substructure and foundation is reduced.

ü Strong adaptability: It can be designed as equal cross-section or variable cross-section, and the cross-section of a single box and a single chamber, a single box and multiple chambers or a multi-box and multiple chambers can be flexibly selected.

3.Product materials

l Roof/Bottom Plate/Web: Orthotropic Steel Plate Structure (with Longitudinal Stiffeners and Transverse Partitions) in Material S355J2 N / S460 (European Standard) or ASTM A572 Gr.50 / A709 Gr.50 (American Standard) or AS/NZS 3678 Grade 400 (Australian Standard)

l Stiffener ribs: flat steel ribs, ball flat steel or closed longitudinal ribs (U-ribs), the thickness of the U-ribs is recommended to be 6–8mm

l Diaphragm/transverse frame: solid belly type or truss type, arranged according to 3–5m spacing

l Connection method: factory splicing and on-site ring seam with full penetration welding (AWS D1.5 / EN 1090 EXC3-4); Temporary bolt positioning

l Anti-corrosion system: the internal closed environment adopts a dehumidification system and simple coating; The exterior is hot-dip galvanized, metal sprayed or multi-pass epoxy zinc-rich coating system

4.Design features

Ø Section composition

² Single box and single room:suitable for bridge width 8–14m, the best economy

² Single box and multiple chambers: suitable for bridge width of 14–25m, adding a web to reduce the span of the top and bottom plates

² Multi-box single chamber:suitable for bridge width > 25m or ultra-wide bridge, the separate box is easy to transport and install

Ø Longitudinal design:equal section is suitable for small and medium-span continuous beams; Variable cross-section (beam height varies according to parabola or polyline) is suitable for large spans, and the fulcrum beam height is about 1.5–2.5 times in the middle of the span

Ø Orthogonal bridge deck:roof thickness 12–20mm, U rib thickness 6–8mm, spacing 300–600mm, focus on checking the fatigue details under wheel load

Ø Stability Control

² The overall stability is controlled by the width and thickness ratio of the floor plate and the spacing of the partition

² Local stabilization controlled by stiffener element width-to-thickness ratio (in accordance with EN 1993-1-5 or AASHTO Appendix B)

Ø Fatigue design:focus on details such as U-rib-roof welds, U-rib-diaphragm intersections, and on-site splicing ring joints

5.Core Advantages

⭐Absolute Advantage in Torsional Stiffness:Closed-section torsional stiffness is extremely high. Under curved bridges, skewed bridges, and eccentric load conditions, deformation and stress distribution are uniform, without the need for additional torsional reinforcement.

⭐Outstanding Spanning Capability:For constant-section steel box girders, economical spans range from 40–80m; variable-section spans can extend to 100–150m, suitable for pier-free river crossings.

⭐Minimal Construction Interference:Segments prefabricated in the factory allow rapid on-site assembly; construction can use pushing, hoisting, or scaffolding methods, with minimal impact on traffic or navigation below.

⭐Reliable Fatigue Performance:Orthotropic bridge decks have been proven in decades of projects. Coupled with improvements such as bolted U-ribs, they meet fatigue life requirements under heavy traffic.

⭐Life-Cycle Economy:Lightweight reduces substructure costs; steel is recyclable; combined with long-term corrosion protection and internal dehumidification systems, a design life of 50–100 years can be achieved.

6.Compliance Standards

7.Why choose us

Choosing our steel box girder bridges means you are choosing a professional team that highly integrates structural efficiency, manufacturing precision, and on-site constructability. We do not just provide steel structure tonnage—we provide a complete traceable documentation package: from orthotropic plate fatigue detail checks, segment division and transportation feasibility analysis, to welding procedure qualifications (WPS/PQR) and NDT inspection plans in accordance with EN 1090 EXC3/EXC4 or AWS D1.5.

📧Satisfied after reading? Feel free to contact us, we look forward to working with you🤝