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GWR Route: Banbury to Wolverhampton

Olton Station: gwro2694

A useful illustration of typical construction details involved in Brunel’s wrought iron balloon–top plate girder bridge beams

Although not of a Warwickshire bridge, this photograph provides a useful illustration of typical construction details involved in Brunel's wrought iron balloon–top plate girder bridge beams. The section through the tubular flange was cut during this bridge's replacement in 1953 - the bridge having been originally built over one hundred years previously in 1848. The vertical iron plate would only have been within the tubular flange at the bridge ends, where the balloon-top curved down. The plate girder has vertical web stiffeners at regular intervals and the riveted joints in the balloon-top are butt-type with a curved cover plate or butt-strap. Normally there would be a second butt-strap on the other side of the main plates being jointed (in this case inside the tubular flange) and both these butt-straps would be 75% of the thickness of the main plate. This made a stronger joint than a lap joint arrangement, due to the equal forces produced by the double shear on each rivet.

Robert Ferris

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