Fatigue-Resistant Closed-Section Steel Box Girder Bridge per AASHTO LRFD

The steel box girder bridge adopts a closed box-shaped section composed of Q355 or higher high-strength steel and orthotropic steel deck panels. Longitudinal U-ribs and transverse diaphragms are arranged on the top and bottom plates to form a stable structural system. The product highlights include light self-weight, high torsional stiffness, factory sectional prefabrication, and rapid on-site hoisting. Materials are selected from weathering steel or epoxy zinc-rich heavy-duty anti-corrosion coating systems. The design supports flexible adaptation of equal height or variable height, and vertical or inclined webs. It is widely used in highway bridges, urban viaducts, railway bridges, interchange ramps, and pedestrian overpasses with spans ranging from 30 to 200 meters.

1.Application Scenarios

2.Product Highlights
✔Lightweight with strong spanning ability: High-strength steel with low self-weight can significantly increase span capacity compared to concrete beams and reduce the number of bridge piers.

✔High bending and torsional stiffness: The closed box section has extremely high bending and torsional stiffness, making it especially suitable for curved bridges, skew bridges, and eccentric load conditions.

✔Factory manufacturing with controllable quality: Steel plate cutting, welding, and coating are all completed in the factory, ensuring high precision, easy control of weld quality, and minimal impact from on-site environment.

✔Fast construction with minimal traffic disruption: Segmental prefabrication, on-site lifting, or push-launch construction can be used to greatly shorten on-site work time, making it suitable for busy traffic areas.

✔Good durability and low life-cycle cost: When combined with high-performance anti-corrosion coatings or weathering steel, long-term protection can be achieved and maintenance costs controlled.

✔Attractive design with strong adaptability: The bottom slab of the box girder can be designed as straight, segmented, or curved according to requirements; the web plate can be designed as a straight or inclined web, providing a simple and modern appearance.

3.Product Materials

4.Design Features

●Closed Section Form: Typically uses single-cell single-box, single-cell multi-box, or multi-cell multi-box sections, forming a closed structural unit that significantly increases torsional stiffness, suitable for curved bridges and eccentric loads.

●Orthotropic Steel Deck (commonly used): The top plate, longitudinal stiffening ribs (U-ribs, plate ribs), and transverse diaphragms together form an orthotropic plate structure, reducing self-weight while providing sufficient local stiffness.

●Variable Height Design (as needed): For long-span bridges, the box girder height can vary in a curved or segmented manner according to bending moment changes, optimizing material distribution and reducing self-weight.

●Longitudinal Stiffener Arrangement: Longitudinal stiffeners (U-ribs, L-ribs, or plate ribs) are provided on the top plate, bottom plate, and web to improve local stability of the plates and compressive buckling capacity.

●Transverse Diaphragms and Frames: Solid or truss-type transverse diaphragms are arranged along the bridge at certain intervals to maintain the box girder section geometry, constrain distortion and warping-torsion.

●Web Design: Can use vertical or inclined webs. Inclined webs can reduce the bottom plate width, thereby reducing pier size and improving visual transparency under the bridge, commonly used in urban viaducts.

5.Core Advantages

⭐The barrier-free crossing achieved through incremental:launching construction utilizes a computer-controlled synchronous incremental launching system, enabling the completion of crossing construction without disrupting the underlying traffic or navigation. The precision of a single incremental launching stroke can reach ±5mm.

⭐The fatigue life of orthotropic bridge decks can be predicted:When the U-rib-top plate welds are constructed using double-sided welding or internal welding techniques in conjunction with phased array ultrasonic inspection, the fatigue life can exceed 2 million cycles, meeting the 100-year design benchmark for heavy-duty traffic.

⭐In the variable cross-section optimization:the beam height at the fulcrum is increased to 1.8–2.5 times that of the mid-span, with steel materials concentrated in areas with larger bending moments. The steel usage for the entire bridge is reduced by 15%–25% compared to the uniform cross-section design.

⭐The enclosed section features a corrosion-resistant redundant design:with a dehumidification system installed inside the box to maintain a relative humidity of ≤40%. Coupled with long-lasting coatings or thermal spray aluminum, it can achieve over 50 years of maintenance-free operation, significantly reducing the total life-cycle maintenance costs.

⭐The closed box section, with its high stability against overturning:boasts a lateral safety factor against overturning that can reach over 4.0, significantly higher than that of open sections. It is particularly suitable for bridges with steep cross slopes, small radius curves, and single-support pier top arrangements.

⭐The transportation and installation have strong adaptability:The segment division is optimized according to highway or maritime transportation clearance, with the weight of each single segment controlled between 40 and 80 tons. With the assistance of self-balancing lifting devices or girder launching machines, installation can be carried out in steep mountainous areas or narrow urban spaces.

 

6.Global Standards

Aspect	Relevant Global Standards & Regulations
Structural Limit State Design	Comply with AASHTO LRFD and Eurocode EN 1993-1-1, regulating ultimate limit state and serviceability limit state for box girder section stress and deformation control
Dynamic & Vibration Control	Follow ISO 10137 bridge vibration standard and EN 1991-2, controlling pedestrian comfort and vehicle-induced vibration amplitude of steel box girders
Section Fabrication & Dimensional Tolerance	Implement ISO 12246 and AWS structural steel fabrication criteria, governing plate splicing, box girder geometric tolerance, web and flange assembly accuracy
Fire Resistance & Protective Specification	Adhere to EN 1993-1-2 and ASTM fire protection standards, specifying fireproof coating thickness, material grade and fire endurance requirement for closed steel box structure

 

7.Why choose us

Choosing our steel box girder bridge means that you are not opting for a standardized steel structure product, but rather a bridge solution that is deeply customized for the specific working conditions of the project. We deliver not just drawings and tonnage - we deliver rigorously verified buckling resistance, traceable U-rib weld quality, and segment division logic that perfectly matches on-site construction conditions (jacking/lifting/cast-in-place with supports).

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