The Howe through truss and the Howe deck trusses
Approximately fifteen Howe through type timber truss rail bridges were built between 1897 and 1917, with three remaining in 2021. Six 5 panel Howe deck type timber truss rail bridges were built between 1901 and 1915, with four remaining in 2021. Three 6 panel Howe deck type timber truss rail bridges were built between 1903 and 1915, with only one remaining in 2021.
Howe trusses were invented and patented by American William Howe in 1840. They consist of timber chords intersecting diagonal braces and vertical end posts. The critical innovation in the Howe Truss was the use of wrought iron verticals with threaded ends instead of timber.[21]
The three types of Howe trusses for NSW railway bridges were designed by Henry Deane. Whitton left Sydney for a visit to England in June 1889 and retired in May 1890, without returning to NSW. Deane acted in the role of Engineer-in-Chief until his formal appointment and his quite different approach is suggested by Deane’s official visit to the USA in 1894 and his 1900 paper for the Institution of Civil Engineers in Britain, ‘Economical railway construction in New South Wales’. All timber truss bridges built after 1894 were Howe truss designs. Deane’s designs based on the American Howe-truss bridges are examples of the use of timber as an economical material for bridges on developmental (Pioneer) lines in NSW.
Deane did away with cast iron shoes in his designs, which is different to Whitton and to all the timber truss road bridge designs. The design of timber truss rail bridges took a separate path to the design of timber truss road bridges except for two areas of overlap worth mentioning. One is the use of the Allan (road) truss bottom chord splice detail in the Howe through (rail) truss design. The other is the appearance of H.H. Dare’s signature as “Assistant Engineer” in 1905 on both the Borah and Oakey Creek five-panel Howe deck (rail) truss plans.[22] The shortest remaining timber truss road bridge (65’ over Tunks Creek, Galston Gorge) is longer than the longest timber truss rail bridge built in NSW (of which three remain) at 62’ span.
References
[21]Jeff Brown, ‘The Howe Truss: From Timber to Iron’, Civil Engineering, June 2012, p 41.
[22]Bill Phippen, 2020, The Timber Truss Railway Bridges of New South Wales, ISBN: 978-0-6488842-0-0
