Flexural And Torsional Stiffness Steel Box Girder Bridge Big Loading Capacity

Instruction:

The steel box-girder bridge is generally composed of top plate (bridge panel), beam web, bottom plate, longitudinal stiffener and transverse stiffener, and diaphragm plate (cross beam).

In order to ensure the quality of welds, welding in factory should be adopted as far as possible, and should strictly check the weld quality.

The lower edge of the top plate is welded with vertical and horizontal stiffeners to form an orthogonal bridge panel. 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.

It's important to note that the advantages of steel box bridges may vary depending on the specific project requirements and site conditions. Consulting with a qualified structural engineer is essential to determine the most suitable bridge design and material for a particular application.

Orthotropic steel bridge panels

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.

Structural form of steel box-girder bridge

Single box and multi-chamber: it is rarely used, and the middle belly plate has little influence on the torsional rigidity of the steel box girder.

Double box steel girder bridge

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 (see photo below)

Single box steel beam bridge

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

Interval: 2m~4m (closed rib)

Multi-box steel girder bridge

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.

It is mainly used for suspension bridges in the past because of its large torsional and bending inertia and good wind resistance.

The top plate and bottom plate are usually reinforced with U-shaped longitudinal ribs.

Transverse diaphragms usually adopted solid-web.

It's important to note that the appearance of a steel box bridge can be customized to suit the specific project requirements, surrounding environment, and architectural preferences. Many factors, such as the bridge's location, purpose, and budget, influence the design choices made by the project team. Ultimately, the goal is to create a visually appealing structure that harmonizes with its surroundings while meeting functional and safety requirements.

Longitudinal beam

Effect

When the main beam spacing is large, the span of the reinforced concrete bridge panel should be reduced;

Improve the stiffness of steel bridge panels.

Structure

Longitudinal beam spacing: for reinforced concrete bridge panels, not more than 3m.

For steel bridge panels, when the beams or transverse ribs spacing is small, it could not set.

When the bridge width is large, it can be set.

(3) Beam

Effect

For two or more boxes, made the main beam stressed evenly

Support longitudinal beams or bridge panels

The end beam can effectively improve the overall torsional resistance of the bridge and disperse the fulcrum reaction.

Interval

When there is a longitudinal beam, it is not greater than 6m. (reduce longitudinal span)

Without a longitudinal beam, the maximum value is 20m. (mainly plays the role of lateral load distribution)

When there is a longitudinal beam, it is not greater than 6m. (reduce longitudinal span)

Without a longitudinal beam, the maximum value is 20m. (mainly plays the role of lateral load distribution)

(4) Support and temporary fulcrum arrangement

Multi-box steel beam bridge, one steel box and one support.

When a steel box is equipped with multiple supports, the bearing force may be uneven.

Temporary fulcrum supporting the jack should be provided to strengthen the structure.

3. Mechanical characteristics and structural measures of steel box-girder bridge:

(1) Damage type

Under the action of bending moment, the compression flange is partially unstable and occurs bending failure.

Under the action of concentrated force, the nearby beam web was crumpled failure.

(2)Structural measure

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.

Structural characteristics of Steel box-girder bridge:

Application of of steel box-girder bridge:

Road, rail and high-speed rail

Advantages of steel box-girder bridge:

Floating pontoon bridges offer the advantage of being portable, modular, and relatively easy to assemble and disassemble. They can be configured to accommodate various loads and traffic types, including pedestrians, bicycles, vehicles, and even light to medium-duty construction equipment. However, it's important to note that floating pontoon bridges are typically designed for temporary use and may not have the same load-carrying capacity or longevity as permanent bridge structures.

The flange width is large, with great bending resistance and large span.

Large torsional stiffness, uniform lateral load distribution, suitable for curved bridge.

Advantages of steel box-girder bridge compared with truss girder bridge:

Light weight, save steel

High flexural and torsional stiffness

Quick installation and easy maintenance

Suitable for forming continuous beams

Novelty structure, the shape is simple and beautiful

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