Talk:Box girder bridge

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Surely the box girder's ancestor (or one of them) is the tubular bridge. Stephenson's Britannic Bridge completed in 1850 is often called the world's first box girder bridge. Jooler 13:11, 8 May 2006 (UTC)[reply]

Ancestor perhaps, but these early tubular bridges are not box girder bridges and it's wrong to describe them as such. There are two significant differences:

A tubular bridge places the carriageway inside the tube. That much is unimportant, but it implies (importantly) that the "box" or "tube" is quite tall. This spaces the top and bottom webs further apart, making the overall girder stiffer.
The early tubular bridges used a cellular girder (cf. William Fairbairn) in their upper and lower webs. This also improves stiffness.

So early tubular bridges are actually quite complex. Box girders are a simplification of their manufacturing costs, and this over-simplification without a full understanding of their behaviour under load led to the failures. Andy Dingley (talk) 17:56, 4 August 2009 (UTC)[reply]