A box girder bridge is one in which the principal structural element is one or more closed cells, acting in bending. Box girders are used for highway bridges, railway bridges and footbridges – different structural forms are chosen for each of these applications.

For spans in the range 45 to 100m, multiple girders are used, with the slab spanning transversely between the webs. For such configurations, relatively narrow rectangular steel box sections have sometimes been chosen. However, such sections are rather small and introduce significant hazards for access for construction and maintenance and are rarely chosen now for this span range. An alternative configuration that is now more commonly used employs ‘open topped’ trapezoidal girders. These girders have a steel bottom flange, inclined steel webs and a narrow steel flange on top of each web. The closed cell is formed by the reinforced concrete deck slab. With this configuration, material access during construction can be minimized by the use of permanent formwork (or precast slabs) and for maintenance the cells are larger than those for rectangular steel boxes, thus reducing the difficulties of access.

Steel box girders

For spans over about 200m, all steel construction is often used. The roadway is then carried on a longitudinally stiffened steel top flange, commonly known as an orthotropic steel deck. Such construction is lighter but is more complex to fabricate.

Types of box girders

Advantages of steel box girders, compared to 'I' girders:

*High torsional stiffness and strength, giving greater suitability for horizontally curved bridges, greater aerodynamic stability and reduced susceptibility to lateral buckling of flanges (in lateral-torsional or distortional buckling modes)

*Reduced need for support points

*Improved durability and reduced maintenance of protective coatings (less exposed surface, fewer edges, avoidance of exposed horizontal surfaces, no exposed bracing and stiffeners).

*The clean lines of a closed box girder are also often considered give an excellent appearance, particularly for footbridges where the visual impact is considered to be important.

About FAMOUS

FAMOUS has made a name for itself in the list of top steel structure manufacturers in China. Serving contractors, developers and architecturers worldwide since a decade ago, we have been offering a variety of steelwork fabrication services including, but not limited to:

* Free estimate and technical proposal for your project.

* CAD design engineering service by highly-trained team of professionals.

* Steel structures components fabrication in EU, U.S. and AS/NZS standards for bailey bridge, truss bridge, beam bridge and box girders.

* Steel framing structures fabrication in EU, U.S. and AS/NZS standards for commercial, industrial or residential buildings.