Inglis Bridges
WORK IN PROGRESS
During the First World War Charles Edward Inglis, as director of the bridging department of the Royal Engineers, conceived and produced an ingenious and well thought-out series of transportable steel bridge that could be erected rapidly, and dismantled for re-use. Versions remained in use by the British Army throughout the First World War and the inter-war period, until superseded by the higher capacity Bailey Bridge in 1940–1941.
In 1919 Inglis, by then Professor C. E. Inglis, O.B.E. (Major, R.E.), presented a fascinating Paper describing the development, production, and operational use of the bridges, reproduced in The Engineer under the heading 'Portable Military Bridges'.[1]
The bridge girders are of the Warren truss type, assembled from tubular steel sections joined by cast steel nodes. Referring to the photographs of the Monmouth bridge, the principle of the joints is by no means obvious. In fact they are stiffened pinned joints.
During initial assembly the pins are easily inserted in slots in the node and in the attachment fitted to the tube ends. The slots in the tube end attachments and in the nodes are accurately machined, the load-bearing ends of the slots being machined to a radius corresponding to that of the pins.
It will be seen in Figs 2 & 3 that at the ends of the tubes there are collars with integral lugs. These collars are nuts, with 11 threads per inch. The ends of the tubes are 'swelled' and threaded correspondingly. See drawing below. When tightened up against the machined faces of the nodes, the tubes are put into compression, and the asssembly is considerably stiffened. Hence the term 'stiffened pinned joints'.
An Inglis bridge survives in public use in Monmouth. See Inglis Bridge, Monmouth. Another Inglis bridge crosses the Basingstoke Canal at Aldershot, but it is not in public use. A 50 ft Mk. I bridge, formerly at RAF Sandtoft, was removed and partly reassembled in South Yorkshire, with a smaller section going to the Royal Engineers Museum at Gillingham, Kent [2] A replica Inglis Bridge was erected in a park in Leyland, Lancashire in 2016. Other Inglis bridges survive in Canada, Germany, Pakistan, and on the Simpson Reserve in New Zealand.
The first Inglis bridge were used on the Western Front in 1916. These were widely used in Europe in 1918, replacing destroyed road bridges. Another significant use in 1918 was the Allenby Bridge across the Jordan River.
Each individual part could be readily manhandled. The bridge was built on blocks in skeleton form with a counterbalance arm and jacked up onto a wheeled trolley. It was then pushed over the gap, the counterbalance removed, supported on the abutment, and the decking laid.
Following rapid development and testing, all the production bridges were manufactured by Kryn and Lahy.
Note: Patent specification for Mk I bridge (Charles Edward Inglis) here, and for Mk III bridge (Charles Edward Inglis and Kryn and Lahy) here.