Scherzer Bridges

Taken from;  Civil Engineering Heritage: Ireland
 By Ronald C. Cox

Scherzer Bridges – Royal Canal

O 171 344


The Royal Canal was completed in 1817 to provide a second line of communication between Dublin and the River Shannon.  It joins the river Liffey at Dublin at the North Wall Quays to the west of the East Link Bridge and is crossed at this point by twin lifting bridges.  These bridges were erected in 1912 by the firm of Spencer & Co. of Melksham in Wiltshire to replace a rolling drawbridge placed there by the Midland and Great Western Railway Company in 1860.  Sir John Purser Griffith, Chief Engineer of the Dublin Port and Docks Board, based his design on that previously patented in 1893 by William Scherzer of Chicago.

Each bridge consists of two main girders connected together by 14 floor beams, the floor been composed of patented “buckled plates” (an invention of the Irish Engineer, Robert Mallet, whom you will learn more about during the walk at Broadstone) resting on and riveted to the floor beams and to the joists fitted between the floor beams.  To the western ends of the main girders segmental girders are attached to form the rolling surfaces upon which the bridges bear.  The segmental girders are extended so as to carry a large counterweight and the whole structure is suitably braced.  To prevent accidental displacement of the bridges on their paths, teeth were formed on the cast steel track plates, and corresponding recesses cut and accurately tooled in the curved track plates of the segmental girders.  Each bridge was worked by an electric motor (now removed) , erected on a platform in front of the counterweight box, they could be operated manually in case of power failure.

A similar pair of bridges was erected by Sir William Arroll  of Glasgow in 1932 over the entrance to the Custom House Docks further up river (O 166 364).  A 1:40 scale model of the bridges can be seen in the foyer of the museum building in Trinity College, Dublin.  The advantage of twin bridges  was that the stoppage of quay traffic when vessels needed to enter or leave the canal system was reduced to a few minutes by alternately raising and lowering each bridge during the locking procedure.

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