Number 12 bridge railway accommodation bridge at NZ 191 297

Railway accommodation overbridge, 1842 by John Storey of Darlington, for Bishop Auckland and Weardale Railway Company; the contractor was The Shildon Works Company.

MATERIALS: Cast- and wrought-iron with timber deck and stone abutments.

PLAN: lenticular beam bridge between stone abutments, crossing the railway cutting at a skew angle.

DESCRIPTION: this beam bridge comprises iron, lattice, side girders carried on stone abutments which rise from the tops of the railway cutting. The girders are tied together to form a single lenticular truss, which crosses the cutting at a skew angle. The timber deck is attached directly to the upper chords, giving the bridge a humpback profile. The bridge has span of 86ft 3in (26.29m) and has a timber deck on timber and iron cross joists. The main top member is H-section cast iron and the bottom member is wrought iron flat link chain. There are twelve panels to the trusses incorporating 11 verticals of round bar with diagonal flats alternately rising and falling. An additional lower bottom member is of square bar and is coupled to the chain of the truss by cast clamps which carry the cross tie-rods. There are horizontal and vertical cross bracings of wrought iron flats. The abutments are built from squared, tooled blocks and have faces that break forward slightly beneath each girder. The hinges of the truss rest on stone or concrete blocks, with angled tops, that are set back from the abutment faces. The timber parapets are renewed, and the timber deck was replaced in 2009.