encountered, had it been attempted to achieve the requisite sectional area in a solid mass") In some ways this isn't a "cellular girder" as such (compared to a spaceframe or geodesic construction) as the cells don't share loads from the entire girder, but merely act to stiffen one plate in isolation. Design of such complex integrated structures requires mathematical modelling techniques in advance of Fairbairn's day. 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 larger truss at Chepstow. However, although many of the longest-span railway bridges in use in the 1860s used tubular or box girders Benjamin Baker in his Long-Span Railway Bridges was already dismissing the 'box girder with web plates' as 'the most unfavourable type for long-span railway bridges which it will be necessary for us to investigate'. The Coronado Bay Bridge has the tallest box girder. Box girder bridges of shallow rectangular cross-section and aerofoil characteristics became extensively used in road bridges from the 1960s onwards, such as the Severn Bridge, being much lighter than the deeper truss-type girder construction used on previous bridges such as the Golden Gate Bridge. 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. That led to serious concerns over the continued use of box girders and extensive studies of their safety, which involved an early use of computer modelling, and was a spur to the development of finite element analysis in civil engineering. See also Hollow structural section Structural steel Bridges Tubular bridges Britannia Bridge Conwy Railway Bridge Box girder bridges Severn Bridge Cleddau Bridge West Gate Bridge Koblenz Bridge Gateway Bridge, Brisbane, Queensland, Australia References Girders sv:Lådbalk Scottish inventions