Expert gives possible explanations for US bridge collapse
(3 August 2007)
A Durham University expert gives some possible explanations for the collapsed bridge in Minneapolis.
Professor Roger Crouch from the School of Engineering stresses the importance of finding the cause soon to ensure other bridges can be protected and pinpoints weather conditions and design as possible causes. Professor Roger Crouch said: “It is important that the true cause of the bridge collapse in Minneapolis is quickly discovered so that civil engineers can re-examine similar constructions worldwide. “While unlikely to be the principal cause of the failure, it was reported that the temperature in Minneapolis had been very high recently. If not properly designed, the expansion of the steel sections exposed to direct sunlight could lead to additional stresses which would exacerbate the problem. “Structural engineers anticipate all plausible forces when designing bridges and add load factors for the material strength and applied loads to achieve the desired level of safety. However, design and construction are not the end of the story for a bridge engineer. A programme of regular inspection and maintenance is essential. “This is the somewhat less glamorous, but vital part of engineering. Inspection requires skilful interpretation of defects caused by accidental overload or corrosion. “There are some concerns that this bridge had a low level of redundancy. If this was the case, it could mean that the structure might not survive failure of one part of the bridge, and might lead to a progressive collapse of the complete span. Local overstressing of a compression member in the arch truss could lead to buckling and a sudden re-distribution of the forces in the remaining structure. If those adjacent members cannot support the additional loads, then collapse can occur.”