John Bradfield's Doctoral Thesis.
The name universally associated with the Sydney Harbour Bridge is that of John Bradfield. Usually appended to the name is the title ‘Doctor’. While some references mistakenly refer to this honorific as being the award of a ‘PhD’ to the man, in fact the degree which bestows the title is a Doctor of Science in Engineering, given by Sydney University in 1924. The degree had never been awarded before and would not be awarded again until the 1970s.
This was not a question of Bradfield undertaking a course of study or research in some engineering subject separate from the bridge. The thesis which was the basis of the degree was about the bridge and public transport in Sydney. The years of research and study which other students seeking a higher degree undertake was in Bradfield’s case all the years he had spent designing the bridge and railway, and by 1924 to some extent, building the underground railway.
The thesis document comprises 284, landscape format typed pages. This format was probably chosen to facilitate the inclusion of many photographs, tables and plans. As is keeping with the era in which it was prepared, before word processing computers, there are numerous overtyped and inserted corrections, and exotic symbols not available on a 1923 keyboard are hand-written.
Bradfield signed his thesis on 26 December 1923 – his 56th birthday. This was a convenient date as tenders for the construction of the bridge closed three weeks later on 16 January 1924. The thesis needed to be completed and submitted. He would lock himself away with his secretary Kathleen Butler and assistant engineer Gordon Stuckey for the month after the opening of the tender box to assess the submissions and prepare another document – the Report on Tenders.
In April he would lose his secretary, (and probably the typiste of his thesis), as he would send her to England to negotiate details of the contract with Dorman Long and Co, the winning tenderers. He would follow three months later, and it was during the latter half of the year, while he was in England, that he learned of the success of his submission ad the award of the degree.
The Thesis.
The thesis begins with an introduction setting out the role of engineering in society as he sees it. This is shown in the image adjacent and also quoted on the Main Page of this website.
In an extraordinary passage, Bradfield then acknowledged the support he had been given in the task of designing and building a transport solution for Sydney by his Confidential Secretary, Kathleen Muriel Butler. The only other person thanked is William Warren, Bradfield’s first teacher and Professor of Engineering at the University. Warren was still alive but near the end of his life.
The Problem.
Bradfield details the transport issues facing Sydney. He looks at growing populations and where they live and to where they commute for whatever reason.
The Suburban and City Railways.
Most particularly for electric commuter railways he then goes into detail about the design of carriages and the inherent limitations of frequent trains stopping at closely spaced stations.
The story then becomes one of describing the history of the construction of the City Railway from 1915 until cessation of work in 1917; its resumption in 1922 and progress from that date until the current time.
To complete this study of the railway aspect of the city transport issue the thesis then looks at the administration and cost control of the work as it is being undertaken.
The Bridge.
Bradfield begins this section of his thesis by looking at the ‘ancient’ history of the bridge - Francis Greenway in 1815, Peter Henderson in 1857 and the several enquiries and design competitions. This information is the first chapter of any history of the bridge but just who put it all together the first time is unclear.
He then moves into looking at the gross design of the bridge. He considers the size of ships, particularly the height of their masts, and looks at other major bridges throughout the world to decide the required navigation clearance. He looks at the likely traffic for rail and road to determine the capacity of the deck in terms of lanes of road or lines of railway.
With this gross concept given, he then turns to the material available to build such a bridge – steel. Many variations in the material are considered from the common relatively cheap carbon steel through various better alloys to more exotic high-alloy steels with nickel and chromium.
The next section looks at the three basic designs available for a long span bridge – suspension, cantilever and arch. He looks at existing bridges and their spans and loadings. The thesis considers the complicated economies as spans increase and the practical limits for the several types.
The design specifications for the proposed bridge are then discussed. The intensity of loading and its likelihood of occurrence is considered. For example, he imagines that on some occasions during public festivities the bridge pedestrian ways could be jam-packed with spectators, and this is the source of his design live load for that component. He considers that the possibility of the maximum weight train occupying the exact same location on all four bridge railway lines is remote, so he applies a reduction factor.
The considerations for the cantilever and the arch are discussed separately. In view of the fact that the arch is the bridge that was built, the section is here transcribed:
ARCHES: Long span steel Arch Bridges are of two types, viz., Three-hinged and Two-hinged. Three-hinged arches are not generally used for medium span railway bridges because they are less rigid then two-hinged arches, but for long span bridges they have advantages for erection purposes.
The statical action of an Arch is the direct inversion of the section of the Suspension Bridges. Loads are transferred from the floor to the arch rib and transmitted direct to the abutments – the rib itself being in direct compression. For this reason the arch is the most rigid of all types of structure; the Simple Span and the Cantilever both act in bending, and more flexure is produced in this way than by the effect of direct compression.
The largest arch span yet proposed was for a bridge across the Hudson River, New York, designed by Max am Ende, in 1889, span 2850 feet, rise 440 feet. When the Forth Bridge was under consideration Max am Ende also designed, in 1880, an arch bridge of 1640 feet span with a rise of 395 feet.'
As an alternative to the cantilever design for the Quebec Bridge, Mr. Charles Worthington of New York proposed a voussoir arch od 1800 feet span; the foregoing proposals were never carried into effect.
The most notable Arch Bridge yet erected is he Hell Gate Arch at New York, with a span of 997.5 feet, carrying four railway tracks for heavy steam freight services. This bridge under full live load o 24,000 lb.pr foot deflects only 3.82 inches at the crown, and under minimum temperature sinks a further 5.30 inches.
A two-hinged or three-hinged braced arch is the nest type for railway traffic when the abutments permit of sufficient rise, which is usually the case when the arch type of bridge proves to be the proper solution. A two-hinged or three-hinged arch is more rigid and less subject to vibration than any other type of bridge, and has the advantage of easier erection as each half can be erected as a cantilever arm held back by suitable temporary anchorages until the centre connection is made. The Arch possesses another advantage over other type, because for live and dead loads the web stresses are relatively small, but high web stresses are involved in the erection. Consequently, sections designed for the requirements of erection automatically provide for heavy concentrations of loading due to or in excess of specified requirements.
Preliminary investigations on a two-hinged Arch Span of 1,550 feet with a rise of 310 feet, with a rib depth at the crown of 60 feet showed that the deflection at quarter points with live load covering half span was approximately 8¾ inches. The maximum deflection at centre, with centre half loaded was 7 inches, and the rise or fall at centre, with a temperature variation of 60 degrees F., was approximately 7½ inches.
As an Arch Bridge either two or three-hinged is very suitable for heavy railway traffic, and various firms asked to be allowed to tender for and were prepared to guarantee the erection of an Arch Bridge, the author prepared and included an alternative to the Cantilever Bridge design for a two-hinged Arch Bridge of 1,650 feet span, but tenderers could tender for a three-hinged arch if they so desired.
A detailed stress analysis for both types of bridge is then presented leading to diagrams showing forces in all the members and cross-sectional areas for each.
Both types of bridge are then described and illustrated in detail, followed by a description of the erection techniques. Strangely there are 8 pages devoted to the cantilever, with several illustrations of the floating out of the suspended span and a detailed plan of the hoisting mechanism, but only two sentences to the arch bridge.
The Arch Bridge will be erected by cantilevering out from either pier until the end meets at the centre, when the final riveting up will take place. Each half of the Arch will be securely anchored and tied to the shores on either side until the central connection is made.
The arch was a later addition to the options in the call for tenders, so perhaps the drawings and sketches for the cantilever had been long prepared, but no time was available to make similar illustrations for the arch.
A significant section is then devoted to traffic diversions during the construction. Ferry wharves have to be relocated from Milsons Point and the railway station at the same location moved to a less accessible location further along Lavender Bay.
Town Planning
The town planning implications of the new transport routes are then discussed. Wonderful illustrations of the proposed redevelopment of Lavender Bay are provided, but it is never stated whether these were specifically prepared, by Bradfield, for the thesis or whether they were drawings prepared for more general use in the Public Works Department.
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A detailed proposal for widening of streets, and new streets carved through the city is then given. Bradfield admits that these plans have been endorsed by a committee of the City Council and must therefore be pre-existing of the thesis. It should also be noted that this entire section had been published in ‘‘The Sydney Mail’’ two months earlier as ‘Written by Kathleen Butler, from the Notes of Mr. J. J. C Bradfield, Chief Engineer, Sydney Harbour Bridge.’
The final section of the document looks at the finances of the bridge. Two-thirds of the cost is to be met by the Railway Commissioner though at the train fares proposed the investment should be a remunerative one. One-third of the cost is to be borne by the ratepayers of areas of the city and suburbs benefitted by the bridge through a levy on land values and this would also seem to be a financially sound proposition. In 1924 there is no mention of a toll for road users of the bridge.
Bradfield concludes the thesis by stating that all the work in it is his and therefore worthy of the award of the degree. It is here reproduced and offered for scrutiny. Perhaps the plan as realised in 1932 had many parents, and others than Bradfield had made a contribution?
Conclusion. As required by the laws, in concluding this thesis I certify that all the proposals herein contained and approved for construction were originated by me. (a) The Metropolitan Railway as located. (b) The extent of the electrification. (c) The location of the City Railway partly elevated and partly underground, notwithstanding that the Royal Commission on the Improvement of the City of Sydney and Suburbs reported in favour of the wholly underground scheme put forward by the then Chief Commissioner, Mr. T.R. Johnson, who subsequently concurred with my location. (d) The bridge as located and designed from Dawes’ Point to Milson’s Point notwithstanding a Royal Commission on Communication between Sydney and North Sydney had reported in favour of three separate subways for railway, tramway and vehicular traffic. (e) The location and design of all stations on the City Railway, and on the railways proposed to the eastern, western and northern suburbs. (f) The proposal to convert Milson’s Point Railway from Lavender Bay to Milson’s Point into a Park, the proposal for Catherine Crescent at the Bridge head connecting the main avenue from the bridge with York, Clarence and Kent Streets and the parklets shown. (g) The portion of the scheme of the new streets and street widenings coloured red, necessary in connection with the future traffic of the City and recommended to the City Council.
See the complete thesis by following this link: https://ses.library.usyd.edu.au/handle/2123/11968
