High Level Bridge - Design

Design

Designed by Robert Stephenson and built between 1847 and 1849, it is the first major example of a wrought iron tied arch or bow-string girder bridge. It is a fine and long standing engineering solution to a difficult problem; the spanning of 1,337 feet (408 m) of river valley, including 512 feet (156 m) across water. The High Level Bridge has six river spans of 125 feet (38 m) length,.sitting on masonry piers 46 by 16 feet (14 by 4.9 m) in section and up to 131 feet (40 m) height. There are also four land spans on each side, of 36 feet 3 inches. The single carriageway road and pedestrian walkways occupy the lower deck of the spans, 85 feet (26 m) above the high water mark, and the railway the upper deck 112 feet (34 m) above the high water mark. The total weight of the structure is 5,000 tons.

According to a contemporary encyclopedia:

Each river span is crossed by four main cast iron arched ribs, with horizontal tie bars. The roadway is situated between a pair of ribs some 20 feet apart; and walkways are sited on either side of the roadway in a 6 foot gap between the central and outside ribs. The upper, railway, platform, rests on the arches of the ribs, whilst the lower roadway is suspended from the ribs on wrought iron rods. Each arched rib was cast in five sections. Besides the tie-bars, the ribs are braced by horizontal and vertical bracing frames, while diagonal bracings are inserted in the spandrels, or spaces between the arches and the girders which carry the railway. On the tops of the spandrel pillars, girders extend length-wise, from which other stretch at right-angles across the arched ribs. The whole thus has a perfectly rigid character and is found to bear the heaviest weights without deflection.