Box girder

As a box girder or box girder construction, a carrier will be referred to, the cross -sectional shape enclosing a hollow space. The cross-sectional shape giving a high stability of the carrier, similar to a pipe. Box girders are used for the superstructure of beam bridges as well as for the bow of arch bridges, but can also be used for other structures. Vertical components with a hollow core such as large piers are not referred to as hollow box, but as " components with hollow cross section."

Properties

Construction

A hollow box, in its simplest form consists of a bottom plate, two side members and a cover plate enclosing the cavity. The cavity has a generally rectangular or trapezoidal cross-section, but it could also be triangular, if no base plate is used. Top and bottom plate are also referred to as belts, the longitudinal members as webs. In addition to the two webs, which bound the cavity outwardly of the cavity located on the inside by means of additional webs may be divided. The individual cavities are referred to as cells. Accordingly, a hollow box without additional inner webs is referred to as a single cell, such as a double cell with a partition, and so on. The interior of box girders are mostly accessible for inspection and maintenance purposes.

Mechanical properties

The mechanical properties are comparable to those of tubes or those of the naturally growing bamboo. The sectional shape of box girders gives a high stiffness, both the bending and torsion on. Due to the comparatively distant from the centroid walls of a hollow box results in a large bending modulus. The round closed wall also enables a large Torsionswiderstandsmoment.

Furthermore kink support this construction under longitudinal compression not as fast as bars with the same cross- sectional area, but more compact cross-section geometry, which is due to the lower slenderness with the same material used.

Materials

In bridge today most hollow boxes made of reinforced or prestressed concrete, but it also comes welded structural steel used. For girder bridges with box-girder steel composite construction that consists of a bottom plate and bridges made ​​of structural steel, covered with a deck slab of reinforced concrete. The connection of the concrete slab with the steel parts is done by the headed studs.

Use

For girder bridges on or multicellular hollow box girders are used. The cover plate is usually used as a pavement slab, and often protrudes beyond the longitudinal carrier addition. The cavity often has a trapezoidal shape. The projection may be supported by additional struts between the base plate and cantilever.

In arch bridges are often used hollow box girder of reinforced concrete for the arch is used, the roadway is supported on the carrier by slender columns.

As an example of the use of bridge outside the Moses Mabhida Stadium in Durban was called, whose roof is supported by a landscaped as a bow box girder.

History and Development

The first box girder bridges were built in 1849 Conwy Railway Bridge and the Britannia Bridge, built in 1850 in Wales. In these bridges, the road was within the composite riveted wrought iron plates carrier, which is why the buildings bridges tube were called. The British engineer Robert Stephenson was commissioned to build the bridges and the mathematician Eaton Hodgkinson drew added and the Scottish naval engineer William Fairbairn. Fairbairn had previously dealt with the structural behavior and the optimization of cross-sections. The approach chosen for the Britannia bridge box girder construction was clearly viable than expected, so that a previously scheduled suspension of the carrier on chains was not necessary.

Also in 1850 Fairbairn first used a hollow box cross-section of a steam-powered port crane. The box girder for the arcuate crane boom was riveted wrought iron plates.

As the first bridge in the world with hollow steel box applies the 1948 finished Deutz Bridge in Cologne.