Work on the bridge in England and Australia in 1924.
A review by Kathleen Butler, written from the notes of J. J. C. Bradfield, D.Sc. (Eng.), M. Inst. C.E., Chief Engineer. The writer recalls the principal events in connection with the great work during the past year, and gives details, hitherto unpublished, of the steel tests carried out at the works of Messrs. Dorman, Long and Co., in England. The review is of especial interest because of the ceremony fixed for to-morrow — the laying of the foundation-stone of the southern abutment tower at Dawes Point.
WORLD-WIDE tenders were called for the bridge, returnable on January 16, 1924. These were reported on by the Chief Engineer (Dr. Bradfield), and the tender of Messrs. Dorman, Long, and Company for the erection of a two-hinged arch bridge in accordance with Dr. Bradfield's plans and specifications was accepted, the contract being signed by Mr. R. T. Ball, M.L.A., Minister for Public Works and Railways, on behalf of the Government, and by Mr. L. Ennis, on behalf of the contracting firm, on March 24th, 1924, the amount being £4,217,721 11s 10d — one of the largest contracts let in the world's history.
In order that vacant possession of the Milson's Point station site could be given to the contractors with the least possible delay, the construction of the Northern Railway approach to the bridge was authorised by the Minister from Bay-road to the proposed North Sydney station some six months before tenders for the main bridge were returnable. By this action the Minister inspired confidence, and the tenders for the bridge were from all points of view satisfactory.
On Saturday, July 28th, 1923, the ceremony of the turning of the first sod look place at the site of the North Sydney station, and on the following Monday Dr. Bradfield began construction of the approach by day labour. The work involved extensive open-cut rock excavation and embankments between Bay-road station and Bank-street, the construction of a reinforced concrete arch bridge over Euroka-street, with heavy retaining walls on either side, and the construction of a reinforced concrete girder bridge carrying the roadway traffic along Bank-street over the four railway tracks below. It also involved the construction of two double line tunnels, which will emerge at North Sydney station as four single-line tunnels. To this station the goods traffic conducted at Milson's Point will be diverted.
The perspective elevation published elsewhere in this issue depicts Dr. Bradfield's vision of how Sydney's arch bridge will appear in 1930.
[The 25 March 1925 issue of The Sydney Mail had another article about the Sydney Harbour Bridge as a double-page spread on pages 20 and 21. The image here cited to is reproduced to clarify this reference.]
Perhaps the best idea of the perspective of the great structure is to be gained by comparing it with the chimney on the Mining Museum building to the left of the picture. This is one of the best-known landmarks on Circular Quay. It is over 200ft high, yet is less than half the height to which the apex of the span will reach.
IN the early days of May [1924] four Australians — Messrs. Stuckey, Holt, and Powys (three graduates in engineering of the Sydney University), and the writer — saw the coastline near Fremantle fade miles away into the blue horizon as we journeyed on our way to check “all drawings, calculations, etc." without delay, as specified by the Chief Engineer when drafting the specification in 1921. Pending Dr. Bradfield's arrival some months later, I, as his confidential secretary, was empowered to carry on all correspondence and discussions with Messrs. Dorman, Long, and Company, the contractors, and to have charge, of the office, which I opened at 4 Central-buildings, Westminster, on June 16th, almost in the shadow of Westminster Abbey and Parliament House. During the stay of the staff in England an opportunity was afforded them of visiting the works of Messrs. Dorman, Long, and Company, also the works of the Darlington Forge, a brief description of which and the work undertaken there in connection with the bridge will be given.
At Messrs. Dorman, Long, and Company's Britannia Rolling Mills and Constructional Works at Middlesbrough, angles, tees, channels, and other shapes are rolled; here also bridge and other constructional work is fabricated. Most, of the rivets used in the fabrication of the main arch span of the bridge will be 1¼-inch in diameter, and will have "grips" up to 9½-in., the "grip" being the total thickness of plates and angles held together by the rivet when "snapped." In a work requiring some 2½ million rivets every precaution must be taken to ensure that the rivets will completely fill the holes drilled in the steel plates and angles, and that the riveting is as perfect as is humanly possible. To ensure perfect field riveting many experiments have been made at the Britannia Works to determine the most efficient shape of rivets and the best method of driving them in the field. As a result of these experiments a rivet tapered 1/32nd of an inch in its length was found to be the best shape to completely fill the holes when driven, also that driving with a pneumatic riveter operating at 1200 blows per minute gave the best results.
This picture represents one of the experiments carried out at Dorman, Long, and Co.'s works to ensure perfect riveting in the Sydney Harbour Bridge. The process is explained in the accompanying article, which also gives technical explanations of the other illustrations on this page.
[The photograph above] shows one of these experiments being carried out; a rivet is being driven horizontally in the bottom chord with a pneumatic (jam) riveter on the outside and a corresponding holding-up machine on the inside; the air pressure was 125lb per square inch. Subsequently the plates so riveted were sawn through the centres of the rivets, and the section showed in what measure the rivets had filled the holes. As may be seen from the photograph, the result was excellent; the plates, 9½ inches in total thickness, are closely held together and the rivets fill the holes. A 1¼-inch diameter rivet of the length required for a grip of 9½ inches is also shown. Experiments were also made with rivets heated by electricity, also by coke and oil furnaces.
The blast furnaces and rolling mills are very extensive. During our visit a charge of 70 tons of molten metal was run into a ladle and thence poured into the ingot moulds. The ingots were heated in soaking-pits and rolled into "blooms," and, after reheating, into the billets from which the various shapes and sections were rolled. The mechanical devices in operation at the blast furnaces, soaking-pits, and filling mills are wonderful, and quite uncanny in their precision. The engineer so devised and controlled these steel automatons that they are almost, human in their action — mind controlling matter for the use and service of mankind, and, on this occasion, for "our harbour bridge."
The heaviest, angle yet rolled anywhere is 8in x 8in x 1in; but the main angles of Sydney's bridge will be 12in x 12m x 1¼in — almost double the weight of the heaviest yet rolled. Interesting tests were carried out on the material specified for rivet steel. In tension the 1¼-inch steel bars had an ultimate breaking strength of 57,500lb per square inch, with an elastic limit of 31,000lb per square inch and an elongation of 31 per cent, in a length of eight inches.
To further test the steel for ductility specimens 2in long, laid longitudinally and set upright on end, were flattened out cold until the material was only ¼in in thickness, without showing any signs of cracking on the edges, proving the ductility of the material to be excellent. The accompanying photographs show specimens of rivet rods before and after flattening out.
Grey Towers, the home of Sir Arthur Dorman, is situated in extensive grounds a few miles from the Britannia Works.
THE Redcar Plate Mills, also owned by Messrs. Dorman, Long, and Co., are situated at Redcar, about seven miles from Middlesbrough, and are the largest, and most, modern plate mills in Great Britain. Here the plates for the bridge will be made. At the time of our visit the first cast of silicon steel was made for "The Bridge". The cast was marked "R.S. 1" i.e., Redcar Sydney No. 1 — and from this cast, plates for the bridge were rolled, whilst some of the billets were drawn into wire to be spun into the cables used for the erection of the bridge.
The chemical analysis of this first cast of steel was as under: — Carbon, 0.330 per cent.; silicon, 0.150 per cent.; sulphur, 0.042 per cent.: phosphorus, 0.030 per cent.; manganese. 0.940 per cent.; nickel, 0.025 per cent.; copper, 0 .014 per cent.; arsenic, 0.021 per cent.
Two specimens of silicon steel tested in tension gave an ultimate strength of 83,700lb and 80,600lb per square inch respectively, with yield points of 47,500lb and 48,000lb per square inch respectively, with an elongation of 25 per cent. and 22 per cent. in a length of eight inches, with a contraction of area of 38.6 per cent. and 35 per cent. respectively. The "necking" of the specimens near the point of fracture, is clearly discernible in one of the pictures, and this reduction in area is another measure of the ductility of the material.
The requirements of the specification were: — Ultimate strength, 80,000lb to 95,000lb per square inch; minimum yield point, 45,000lb per square inch; minimum contraction of area, 20 per cent.; minimum reduction in area 35 per cent. The requirements of the specification were more than fulfilled.
All this may be unintelligible to the ordinary reader. Before explaining what it means, I may mention that Messrs. Dorman, Long, and Company made from the first cast of steel, as souvenirs, jewel-boxes, paper knives, ash-trays, and paper-weights, some of which are shown in the illustrations.
— Jewel case, paper knife, paper weight, and ash tray. Printed inside the lid of the jewel case is this inscription: — "Dorman, Long, and Co., Ltd. Souvenir of visit, October 8th, 1924. Made from first plate of silicon steel rolled at Redcar Works for Sydney Bridge'.
RAILWAY trains, motor and other vehicles, pedestrians, wind and temperature, will produce stresses in the various members of the bridge, tension, compression, shear, and sometimes torsion; in resisting these stresses, the steel will be subject to slight alterations in form as elongation, shortening or bending. These deformations are termed strains. The stress or loading produces the deformation or strain in the material. To enable the engineer to determine what areas of plates, angles, etc., are required, the breaking strength, elasticity, and ductility of the steel must be known, and these are ascertained by testing the steel from time to time as it is made.
A steel bar when tested in tension elongates, and up to a point called "elastic limit," if the load is released, the bar resumes its original, length — i.e., up to this point the steel is perfectly elastic. Just beyond the elastic limit is a point called the "limit of proportionality." where, if the load is released, the steel specimen does not quite come back to its original length, the permanent set being of the order of .0004 inch in a length of eight inches. Above this point the strains increase more rapidly than the stresses producing them, until at the yield point a small increase in stress produces a marked increase in the extension of the specimen. Beyond the yield point the material is tougher and does not extend so rapidly: but the strains increase more rapidly than the stresses, until finally fracture occurs when the ultimate strength of the steel is reached. These points are all clearly seen on the diagram, and are characteristic of all classes of steel.
Bending tests were made to determine the ductility of the steel. Bend No. 1 was made from a plate two inches thick, the specimen being cut in the direction of rolling the plate. The specimen bent, cold around a rod 4½in diameter without any signs of cracking. Bend No. 2 was also cut from a plate two inches thick, but across the direction of rolling, and bent cold around a rod 6in diameter without showing any signs of cracking.
Bend No. 3 was made from a steel plate one inch thick, and, as will be seen from the illustration, it bent cold flat on itself without any signs of cracking, as did also bend No. 4. cut from a plate one inch thick, but across the direction of rolling.
Specimens in the direction of rolling always give better results when tested than specimens cut across the direction of rolling, as when the plates are being rolled the billets receive much more work in the longitudinal direction than in the transverse. All the specimens tested gave better results than called for by the specification. Some of the steel from this first cast was drawn into wire. No. 8 gauge, and subsequently spun into cables, which, when tested at Lloyd's Testing House, Cardiff, were shown to have an ultimate strength of 84 tons, or 188,000lb. per square inch, the individual wires having a breaking strength of 220,000lb upwards. These cables will be used for the erection of the bridge.
A FEW miles across the moors from Redcar is the little seaport of Whitby, renowned in song and story. Here, early in the seventh century, Hilda, a woman of the royal Northumbrian race, built her abbey on the dark cliffs of Whitby, looking out over the North Sea. The ruins of the abbey are one of the attractions of Whitby. Here, in that seventh century, from the lips of Caedmon, a monk of Whitby, flowed the first great English song, he sang of the creation of the world, of the origin of man, and of Christ's incarnation. Whitby is also inseparably connected with the history of Sydney, for here Cook's ship was built, and near here the great explorer was born — at Marton, now a suburb of Middlesbrough, the home of the firm of Dorman, Long, and Company. The house in Grape-lane, Whitby, in which Captain Cook lived is still standing, as is the lighthouse on the pier when he sailed in 1770 on his great voyage of discovery. Cook's monument stands on the Cleveland Hills, and here the ore will be mined to make the plates for Sydney's bridge.
Another place of interest, seen was the monument erected to commemorate the battle of the Standard, fought between the English and the Scotch in 1138.
However, as all things come to an end sooner or later, to an end at last came our most interesting visit to the works of Messrs. Dorman, Long, and Company. In November the staff sailed from England, and, after traversing portions of Canada and the States, sailed from Vancouver on December 17, reaching Sydney on January 10 last.
REVERTING to the more important of the local works: On the Northern Railway approach the tunnel headings were driven day and night ever forward; three heading gangs worked the clock round, shattering foot by foot the elemental strength of the rock until, on June 18, the headings met, in solid rock some 80 feet below "Shore" school gates.
"Opening out" to the full-size tunnel followed closely behind the driving of the headings. The even stratification of the sandstone rock, without any signs of faulting, was remarkable; no timbering was required, and the fluted side-walls and rugged roof of the tunnel as seen unlined were beautiful and almost Gothic in their grandeur.
The tunnel commences as a double line tunnel at Bank-street, but emerges at North Sydney station at two single-line tunnels. Tunnelling is by no means a modern branch of engineering, for as early as 700 B.C. Hezekiah, King of Jerusalem, "bored through the rocks with bronze and fortified his city by leading water into it." To-day the jackhammer chatters its hollow steel drill into the rock at 1200 blows per minute, whilst explosives in the holes so drilled blast the rock to fragments. The practical application of the principles of science has made, vast, strides since Hezekiah's day of hand labour with hammer, chisel, and gad. Sandstone spawls from the excavation
At the site of the "Shore" station open-cut excavation was continued, and the material excavated "lorried" to Lincoln-street, to be used in the construction of the retaining walls there.
The reinforced concrete arch bridge over Euroka-street was completed in July. This bridge is a facsimile of the City Railway bridge over Campbell-street, except that, the latter bridge is faced with sandstone masonry. The bridge carrying the roadway at Bank-street for the railway is a reinforced girder bridge with reinforced concrete slab deck.
The most important happening, however, was the opening of the new Lavender Bay station wharf for railway, tramway, and ferry traffic. The change over was made on Sunday night, July 27, in the interval of five hours between the arrival of the last train on Sunday night from Hornsby and the arrival of the first train in the early hours of Monday morning. In this same interval the tramway to Milson's Point, was diverted along Dind-street and Glen-street to the new station. All operations were well organised and worked without a hitch.
Excavation at Dawes Point for the main abutment tower was commenced on January 19, the first shot being fired on January 22. Another important stage will be reached to-morrow, when the foundation stone will be laid by the Minister for Works.
