The steel box girder bridge is composed of several key components. The top plate and bottom plate, acting like firm "clamps" above and below, mainly bear the longitudinal bending stress. This ensures the stability of the bridge under vertical loads. The web plates, functioning as tough "partitions", effectively transmit shear forces and maintain the overall integrity of the structure. And numerous stiffeners, similar to fine "bones", strengthen the local stability of each plate element, preventing buckling deformation of thin plates under pressure or shear forces, thus enabling the entire box girder to efficiently carry complex loads.

The lower edge of the top plate is welded with vertical and horizontal stiffeners to form an orthogonal bridge panel. The so-called orthogonal shaped plate means the stiffening rib vertical intersection. Due to the different parameters such as the distance and stiffness of stiffeners, the mechanical properties of the ribs are very different in bridge direction, cross bridge direction, relatively save steel, and is very suitable for bearing local wheel load.

The basic forms of longitudinal rib section are open and closed. The cross-section form of the ribs is usually inverted T shape, and its spacing is the span of the longitudinal ribs. In order to enable the longitudinal ribs to pass through continuously, the transverse ribs should be provided with notches.

Box girder is not only the main beam form of beam bridge, but also the main beam form often other long-span bridges, such as suspension bridge and cable-stayed bridge.

Beam: steel deck, which can improve the stiffness of the bridge panel, spacing 1.5m~3m (open rib)

Interval: 2m~4m (closed rib)

Scope of application: when the bridge width is small (3 lanes) or width to span ratio <1/10. For 4~6 lanes, double width single box girder bridge can be adopted.

Effective flange width: main beam web interval <=Le/5

Main beam cantilever length: <=Le/10

Beam lifting: When the reinforced concrete bridge floor is long and the cantilever is long, the lifting beam and the side beam should be set up, and the corresponding transverse partition or transverse rib should be set up.

Scope of application: when the bridge width is large or the single box size, production, transportation, installation is difficult or the effective width of a single box is small and uneconomical.

Beam setting: Can be set or not set

It is rarely used, and the middle belly plate has little influence on the torsional rigidity of the steel box girder.

Scope of application: when the span is small and the bridge width is large.

The main beam is arranged as uniformly-spaced as possible: made the main beam force is uniform.

Adaptability to changing water levels: Floating pontoon bridges can accommodate fluctuating water levels. The pontoons that support the bridge deck can rise and fall with changes in water level, ensuring that the bridge remains functional even during periods of high or low water.

• Under the action of bending moment, the compression flange is partially unstable and occurs bending failure.
• The box girder is distorted under the action of torque
• Under the action of concentrated force, the nearby beam web was crumpled failure.

• Should be provide adequate transverse partitions to avoid distortion and lateral bending
• Should be provide enough stiffening ribs to prevent the local instability of the compression flange.
• Should be arrange a certain stiffening rib in order to prevent local compressive stress or out-of-plane bending in the process of making, transporting and installing the tension flange.
• Transverse ribs and longitudinal ribs should be set up to prevent the buckling of web and local creasing.

• The flange width is large, with great bending resistance and large span
• Large torsional stiffness, uniform lateral load distribution, suitable for curved bridge
• The transverse flexural stiffness is large, the horizontal resistance is strong, and the longitudinal connection can be saved, and the single box can also save the transverse connection
• The single box girder has good overall stability and fast construction
• Small beam height, suitable for overpasses and bridges with limited building height
• Beautiful appearance, transverse and stiffening structure are in the box
• The box is hollow structure, easy to arrange ancillary facilities, repair and maintenance

• Light weight, save steel
• Quick installation and easy maintenance
• Suitable for forming continuous beams
• Novelty structure, the shape is simple and beautiful

• Highway and road bridges
• Railway bridges
• Pedestrian and cycling bridges
• Urban infrastructure
• Overpasses and flyovers
• Emergency or temporary bridges
• Long-Span River and Sea Crossings
• Urban Highways and Overpasses
• Railway Bridges in High-Speed Rail Networks
• Mountainous Region Roadways
• Pedestrian and Bicycle Bridges