- Box girder
A box or tubular girder is a
girder that forms an enclosed tube with multiple walls, rather than an I or H beam. Originally constructed ofrivet edwrought iron , they are now found in rolled or welded steel, aluminiumextrusion s or pre-stressed concrete.Compared to an
I-beam , the advantage of a box girder is that it better resiststorsion . Having multiple vertical webs, it can also carry more load than an I beam of equal height (although it will use more material than a taller I beam of equivalent capacity).The distinction in naming bwetween a box girder and a tubular girder is imprecise. Generally the term "box" girder is used, especially if it is rectangular in section. Where the girder carries its "content" "inside" the box, such as the
Britannia Bridge , it is termed a "tubular" girder. "Tubular" girder is also used if the girder is round or oval in cross-section, such as theRoyal Albert Bridge .Where a large box girder contains more than two walls, i.e. with multiple boxes, it is referred to as a "cellular" girder.
Development of the box girder
The theoretical basis of the box girder was largely the work of the engineer Sir
William Fairbairn , with the aid of the mathematicianEaton Hodgkinson , around 1830. They sought an optimal design for the most efficient design of beam in the new material of riveted wrought iron plates.Box girders in bridges
Fairbairn's theoretical girder appeared at just the right time for the increasing demand for long railway bridges.
Robert Stephenson engaged both him and Hodgkinson as consultants to assist with his Britannia and Conwy bridges, both of which contained the railway track within a large tubular girder. Shortly afterwards Brunel also chose to use a pair of small diameter round girders as part of a largertruss at Chepstow.Safety concerns over box girder bridges
In the early 1970s, a number of box girder bridges collapsed during construction: the
Cleddau Bridge in Wales,West Gate Bridge in Australia and the Koblenz Bridge in Germany. These led to extensive studies of the safety of box girders and serious concern over their continued use. This was also an early use of computer modelling and a spur to the development offinite element analysis incivil engineering .See also
*
Structural steel
*Girder
*Hollow structural section Bridges
*
Tubular bridge
**Britannia Bridge
**Conwy Railway Bridge
*Box girder bridge
**Cleddau Bridge
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