1931 Public Works Department Annual Report.

From Engineering Heritage New South Wales

Page under construction

                    Sydney Harbour Bridge Branch.

                    Report for the year ended 30th June, 1931.

    I have the honour to submit the following report on the work of the Branch for the year ended 30th June, 1931.


    After the curtailment of loan expenditure in the previous year and the consequent leeway to be made up the work was expedited, but, on account of the large amount of unemployment, rationing was introduced in September with a view to absorbing some of the unemployed. The hours were reduced to 351/5 per man per week, worked in 4 days, additional men being engaged so that the work could be kept going for 5 days per week. In January, the hours were reduced to 33 per man per week but in April the hours were increased to 351/5 as an offset against lost time due to wet weather.

    The principal features in the progress of the northern approach were the construction of Kirribilli Station and the Shore local viaduct.

    (a) Excavation.

    A total of 27,361 cubic yards were excavated, the principal items being the regrading west of Kirribilli Station, 5,297 cubic yards; and the regrading of the roadway intersection near Alfred-street, 4,614 cubic yards.

    (b) Concrete.

    The concrete poured amounted to 27,029 cubic yards, 12,763 cubic yards being plain concrete and the balance reinforced concrete.

    (c) Waterproofing.

    The waterproofing carried out totalled 6,314 square yards, being horizontal and vertical mastic over the Shore local viaduct, Kirribilli Station and the Junction-street flat top construction. To protect this waterproofing 1,076 cubic yards of concrete and brickwork were placed.

    (d) Brickwork.

    The platform walls of North Sydney Station were built and, together with the other brickwork carried out, a total of 936 cubic yards were laid.

    (e) Steelwork.

    The broad flange beams of the Junction-street viaduct and the Shore local viaduct were placed, and at the end of June about twenty-five per cent, of the steelwork of North Sydney Station had been erected.

    In all there were 1,634 tons of steelwork erected.

    (f) Plastering.

    Two coat rendering was done on various parapets, pier faces, 120-feet arch, and Walker-street footbridge. These are all of an ornamental character, with dentils, plaques and panels, where the superficial area conveys no hint of the complicated fine work, edgings, mitres, &c.

    The total area was 5,580 square yards.

    (g) General.

    A considerable amount of water service work, drains, &c., were laid, including 30-inch monier pipes under North Sydney Station and the 6-inch fire service to Kirribilli Station.

    There were about 2,000 feet of fencing, both permanent and temporary, erected.

    Portion of the platform awnings of Kirribilli Station was erected, the total area of fibrolite roofing being 5,374 square feet.

    A total of 2,763 lineal feet of kerbing and guttering, equivalent to 282 cubic yards of concrete, were poured.

    Large areas of footway and roadway surfacing were carried out.

    A commencement was made with the plate-laying, the track through North Sydney Station being located in its permanent position and some of the ballast being placed in the tunnels.

    In addition to the above there were various deviations of services for gas, water, P.M.G. cables, and electric cables.

    The steel arch being carried out by Clyde Engineering Co. was commenced about the end of 1930 and at the end of June the two ribs were erected.

                    2. CONTRACT OF DORMAN, LONG AND CO., LTD.

    (a) Concrete and Masonry.

    Pylon construction, which at the end of June, 1930, was at the slab level 155.50, was restricted to the building of the overhanging side balconies from July until September, 1930, as the cable supporting the arch prevented work on any other section. This did not cause any serious delay as the corbelled masonry required a lot of steel formwork and was of necessity slow work. From the beginning of September until the middle of November, the cranes used for setting masonry were occupied most of the time lowering the anchorage cables to the ground preparatory to the re-winding them, but from then on excellent progress has been made.

    The pylons on both sides of the harbour are now above the level of the intersecting arches. The work round this level required a lot of accurate setting of masonry arch rings and careful formwork for the concrete vaults. This work is now stripped and looks well from both the constructional and architectural viewpoints. Dawes Point is further advanced than Milson's Point, and at 30th June, the approximate level of the pylon at Dawes’ Point was R.L. 237, and at Milson's Point R.L. 223. The finished level for the masonry on both pylons is R.L. 285, and the set back concrete cover is another five feet higher.

    After a considerable amount of laboratory research on coke concrete a mix was decided on, which gave a strength, using the high-grade cement now produced by all the cement manufacturers in New South Wales, equivalent to that obtained a couple of years ago with blue-metal concrete and of only 60 per cent. the weight. Satisfactory supplies were obtained from the metallurgical coke used by Australian Iron & Steel Ltd., and a start was made to concrete the roadway deck of the northern approach spans on 11th September, 1930. This work, held up from time to time as the output of the pant at Port Kembla was not large enough to keep pace with the demand, was completed on 14th November.

    A start was made with the southern approach spans deck on 13th March, 1931, but, as a further satisfactory source of coke supplies had been found at Bellambi, this section, although larger, was completed in a month.

    Trough plates for the main arch roadway were all riveted in position on the northern half during May, 1931, so that on 1st June, a start was made to place coke concrete from the centre of the arch northwards. Supplies of coke came forward as required and this section (i.e., the half arch) was completed at end of June, except for portions which cannot be completed until the falsework for the cranes erecting the pylon at Milson's Point is dismantled.

    The Neuchatel Asphalte Co. Ltd., who are the sub-contractors for the laying of the roadway and footway pavement, made a start on the roadway of the northern approach spans on 20th November, 1930. The material used is rock asphalt. This was heated on the site and steady progress maintained until the completion of this section early in January, 1931.

    The pavement of the roadway of the southern approach spans was started on 13th May, 1931, after the heating plant had been brought round from Milson's Point. Weather conditions prevented continuous work but good progress was made when possible and at the end of June, the asphalt was laid from the south end of contract to the south pylon.

    To obtain a suitable pavement for the footways several trial strips were laid and finally a soft sheet asphalt was decided on as it was found necessary to utilise a material which would be elastic enough in cold weather to follow the rapid temperature movements of the steel trough plates. The first section started was the western footway of the northern approach spans and both this and the eastern footway were completed in three weeks during February.

    On 23rd March, the first delivery of railway transoms was made to the northern approach spans. These were stacked on the completed surface of the roadway and adzed there. A careful survey of the railway stringers had to be made and the transoms notched to individual dimensions to give an even grade on the top when the transoms were seated on the stringers. These transoms were painted with one coat of oil and three coats of paint before being placed in position and bolted down.

    On the northern approach spans, the railway tracks are on the curve necessitating timber and steel super-elevation packs, and the seatings for these were adzed on spans Nos. 6, 7 and 8. The transoms for spans Nos. 6, 7, 8 and 9 were bolted in position, and the transoms for span No. 10 were adzed on the deck.

    Timber planking 8 in. x 1½ in. for these spans has been delivered. Those planks sufficiently seasoned have been painted, and on the west side of spans Nos. 6and 7 they have been spiked in position on the transoms.

    The railway decking on the southern approach spans is not so far advanced as at Milson's Point. The transoms for span No. 1 are adzed, painted and bolted in position; for span No. 2 they are adzed and being painted, and for span No. 3 they are being adzed at present.

    Small sub-stations have been built in both pylons, and the Chief Electrical Engineer of the Railway Department has now brought the high tension electric cables in and connected them up, giving a supply of electricity for working the painting gantries, and as a source of supply for general lighting and power on the finished structure.

    Stairways have been constructed in both pylons, and these are now in use, and are the only means of access from the ground to the deck.

    During the year the following work was carried out under the various contract schedule items: —

    No. 1 concrete 9,936 cubic yards.
    Granite masonry 3,866 cubic yards.
    Four-cut work on granite masonry 45,870 square feet.
    Coke concrete 3,119 cubic yards.
    Asphalt on roadway 11,853 square yards.
    Asphalt on footways 3,621 square yards.
    Timber 12,975 cubic feet.

    (b) Fabrication of Steelwork.

    There were 3,208 tons of steel delivered to the workshops during the year, of which amount 997 tons came from England and 2,211 from Australia.

    The last shipment of steel from England was delivered to the workshops per s.s. " Mahia '" on 6th November, 1930.

    Shipments of steel from Newcastle, New South Wales, have continued throughout the year.

    The total amount of steel, &c., delivered to the workshops to date amounts to 52,108 tons, of which total 41,353 tons came from England and 10,755 tons from Australia.

    The first shipment of l00-lb. rails was received at the workshops on 16th June, 1931.

    The total tonnage of steelwork fabricated during the year ended 30th June, 1931, was 12,343 tons, comprising practically the five central panels of the arch, all of the hangers and cross girders suspended from the hangers, deck lateral system, railway stringers, roadway stringers and joists, footway spans, roadway parapets and roadway troughs — practically the whole of the deck steelwork.

    In addition to the above steelwork, the main painting gantry and six auxiliary painting gantries were fabricated.

    The graph herewith shows the quantities of material delivered, fabricated, erected in place, and completely riveted since the first steel delivery.

    (c) Erection of Steelwork.

    The main arch was erected by cantilevering out from each shore, the structure being held back by 128 wire cables attached at the tops of the end posts.

    The scheme of erection in the early cantilever stages consisted of attaching numbers of cables to the top. of the end posts to balance the arch, the number of cables being increased as the load on the arch increased. The solid mass of the abutment tower formed a support for the temporary raking strut between the top of the end posts and the top of the abutment tower, against which the cables strained back.

    This "temporary raking strut," rigidly supported at its base, formed a steady support for the arch, and enabled the stress per cable to be considerably increased in excess of the amount necessary to balance the arch. The frictional resistance of the cables round the tunnel face was thereby increased, and the possibility of the cables slipping in the tunnels under the action of wind and temperature on the structure became negligible.

    For the first few panels of the arch it was impracticable to use temporary sway frames at each vertical, as was done later, and if the arch had only been hanging from cables without the raking .struts, the relative deformation of one arch truss in regard to the other, when the jib of the creeper crane was traversed and a heavy member lifted directly over one truss would have been sufficient to produce heavy bending stresses in the bottom lateral bracing, sufficient to bring about collapse of the structure. Many of the members lifted in the first few panels of the arch weighed about 100 tons. The main jib and its carriage, with the member lifted, weighed about 400 tons, a heavy eccentric load. By means of the rigid support formed by the raking struts, the deformations were reduced to a minimum, and the lateral members were not overstressed in bending.

    The raking strut with its rigid base was vital in the early stages of the erection scheme, and without the rigid support formed by the abutment tower its use would have been impracticable.

    At the 30th June. 1930, the erection of the southern half-arch had advanced to the first triangle of the eleventh panel. that is, the lower chord had been erected up to panel point " 4," leaving two further panels to bo erected before closing.

    On the north side the erection of the half-arch had advanced to the eleventh panel, leaving three panels of the lower chord to be erected before closing.

    The cables required for the anchorage were threaded into position round the cable tunnel, through the tunnel saddle and pylon saddle, and the free ends were laid over the front wall of the abutment tower. Each cable is 2.76 inches in diameter, approximately 1,200 feet long from end to end, and is made up of 217 wires, one centre wire .20 inches diameter, and 216 wires each .16 inches diameter. The ultimate strength of a cable is 360 tons as a minimum; the final load carried per cable was 125 tons. The cables were prepared for attachment by cutting to the correct length and fitting with a cast steel socket. To connect the cable to the socket, the cable was passed through the socket, the wires were opened up and cleaned, some wires being bent over at the ends, and the socket forced upwards on the cable until the opened wires filled the bell-shaped mouth of the socket. The whole of the socket, with its contained wires, was heated by blow-lamps, and molten white metal of composition lead 86 per cent., antimony 11 per cent., tin 3 per cent,, was then poured into the socket. When solidified, the socket connection developed the ultimate strength of the cable itself. All socketing of cables was performed in sheds erected on the end of the pylon cross-girder.

    The final anchorage consisted of 128 cables, arranged at the end post in eight horizontal rows of 16 cables each. The cables had two 3-inch bolts per cable, fitted with special thread, nuts, and spherical-seated washers. The bolts passed through the socket flange, and on either side of a pin 11 inches in diameter, which was grooved to allow the passage of the bolts. At the back end of the pin, the bolts passed through a rectangular forged steel saddle, and projected beyond the saddle a sufficient distance to allow the nuts to be slackened off when the cables had to be removed after the arch had met at the centre. The 11-inch diameter pins were seated on large fan-shaped built-up steel link plates, five links in each set, which sets in pairs were connected to the top chord by means of two pins 27 inches in diameter, each 6 ft. 1 in. long. The pins passed through holes 27 inches diameter in the webs of the top chord, which were heavily reinforced by pin plates. The weight of the link plates is taken by the joist on the end of the end post bracket.

    As the erection proceeded, panel by panel, only sufficient cables were attached and tensioned up to balance the arch and to ensure that the permissible load on the raking strut would not be exceeded under changes of temperature. Eventually, at the seventh panel, the whole of the 128 cables were in action, and the raking strut was no longer required.

    When attaching cables, first the anchor bolts and saddles were put in position, and the cable socket was threaded on to the ends of the bolts to a calculated distance, so that the stress in each cable was about 10,000 lb. In order to tension up the cables, hydraulic jacks are used, operating on the back ends of the bolts behind the saddles shown. The jacks thrust against a cross-head bolted on the ends of the bolts and pushed back against the saddle, so that the nuts on the saddle were relieved of stress. When tensioning. the whole cable was jacked up in this way, the bolts moving through the saddle, and the nuts were turned by hand following the movement of the jacks, until the desired load was in the cable, as measured by the pressure gauge on the jack.

    The tension was checked from time to time by vibrating the cables over the length of 133 feet between the end post and pylon saddle. According to the properties of the cables, its span, weight per foot, &c., the stress in the cable is related to its rate of vibration per minute. This formed a check on the equal distribution of load in the cables.

    The heavy members of the first panel on the Dawes' Point side were landed within reach of the creeper crane by the " Titan " floating crane.

    The first member lifted into place was the section of the first panel of the lower chord adjacent to the western bearing at Dawes' Point. This member was put in place on the 26th October, 1928. It weighed 88 tons. The arch trusses were completed on 10th September, 1930.

    The corresponding member of the eastern truss at Dawes' Point, was placed in position on 7th November, 1928.

    The arch was cantilevered out panel by panel, the cables supporting the steelwork as it was built out.

    When thirteen and a half panels had been erected on each side, the weight of steelwork in each half arch was 13,670 tons, supported by 128 cables, the tension on each cable 107.2 tons, the total pull on each system of cables being 27,440 tons, and the thrust on each of the four main bearings basing 17,660 tons.

    To offset the stretch of the cables and the deformation of the structure as erection proceeded, and to allow a sufficiency between the lower chords for the meeting on the centre pins, the end posts of the arch were set back at the top with a rake of 30 inches from the vertical. At the completion of the cantilever stage of the two half arches of thirteen and a half panels each, this backward rake was reduced, by the stretch of the cables and the deformation of the structure to 18 inches on the south aide and 14⅝ on the north side; the gap between the ends of the lower chords at the centre to allow for the meeting of these chords on the centre pins was 31½ inches on the cast, and 31⅝ inches on the west side. These gaps were affected by temperature and could have been 4 ft. 3 in. at minimum temperature due to contractions of the cables and steelwork, and 1 ft. 9 in. under maximum temperature conditions, due to elongation of the cables and steelwork.

    On 7th August, 1930, the bottom chord of the fourteenth panel of the northern half-arch was erected and a short plank gave access across the harbour for the first time. Mr. Holt, of this Branch, was the first person to cross from shore to shore; Mr. Ennis, Director of Construction for the Contractors, was the first person to walk across the gap at the centre of the arch.

    Both half-arches were finished off identically at the centre joint, the lower chord on each side was fitted with a heavy forged steel saddle to enclose a pin 8 inches in diameter. Before closure was commenced the 8-inch pins were set-screwed into the saddles on the southern side, and to provide for the half-arches being out of alignment horizontally and vertically, lateral adjustment was provided by means of 10-inch square locking bolts.

    The fabricated steelwork of each lower chord at the centre joint was machined to receive the steel forgings which enclosed the centre pins 8 inches in diameter.

    On the northern half-arches, each steel forging was carried by two of the four web plates, and between each forging a heavy steel diaphragm was built, having an opening 10 inches square, into which the locking bolt from the truss opposite could engage.

    On the southern half-arches, the 8-inch pins in two lengths wore set-screwed into the steel forgings, and the locking bolt, 10 inches square with tapered point, was placed in the centre between the two 8-inch horizontal pins, and could be thrust forward by an hydraulic jack into the opening of the diaphragm, which would bring the opposite half-arches into line and level.

    To close the gap of about 31½ inches between the half-arches, the nuts on each pair of link bolts connected with a cable wore run forward one by one in successive fleets of 3 inches, 4 inches, 5 inches, and 6 inches, respectively. A fleet forward of 3 inches at each end of the arch closed the gap by nearly 12 inches.

    Each cable was adjusted independently by means of a high-pressure jacking equipment working up to a pressure of 4 tons per square inch; and to ensure that each cable was let out the exact amount determined on for each fleet, special gauges were used to measure the distance the nuts had to be moved back on the' 3-inch link bolts.

    For the first three fleets the hydraulic jacks operated against the back face of the saddle and pushed the 3-inch bolts upwards by thrusting against a cross-head attached to the ends of the bolts. For the later fleets extension bolts were fitted over the ends of the 3-inch bolts when the outstanding length of those was too short for the jack.

    The work was carried out in two twelve-hour shifts until contact was made on the centre pins, which took place after the first and the second fleet of 3 inches and 4- inches respectively had been completed on all the 128 cables at each end of the bridge, and the third fleet of 5 inches was in progress, 37 cables being let out on the north side and 55 on the south side.

    At 11 a.m. on the 19th August, when the gap was 4½ inches between the eastern and 4¾ inches between the western lower chords, the locking bolts were forced home by the hydraulic jacks, to bring the half-arches into correct line and level. Immediately prior to the jacking, the half-arches — mostly caused by temperature — were about 3½ inches out of line horizontally and 2 inches vertically, the sun influencing the half-arch and cables on the northern side more than on the southern, and the eastern truss very slightly more than the western truss.

    The fleeting forward of the nuts was continued until, at 10 o'clock p.m., August 19th, at a mean temperature of 62 degrees Fah., full contact was made on the pins. Messrs. J. A. Holt, B.E., and G. A. Stuckey, M.E., of this Branch, were at the centre when contact was made. The circumstances proved ideal, as the temperature continued constant throughout the night, until it began to increase with the sunrise, which ensured that the half-arches did not draw apart, as would have happened had a fall in temperature caused the cables to contract. Once full contact was made, as the slacking of the cables continued, the half arches bore on the centre pins with an ever-increasing intensity.

    The arch was now in the three-hinged condition except for the residual tension still in the anchorage cables; the rakeback of the end posts at this stage had been reduced to 5⅜| inches on the south and 5⅝ inches on the north side; the half-arches had dropped 4 ft. 1¼ in. at the centre, due to the fleeting forward; and immediately prior to meeting, the centre pins were 348 ft. 6 in. above the level of the centre of the pins in the main bearings at the abutments.

    The third, fourth, and fifth fleets of the nuts were completed when the tension in the cables was reduced sufficiently to admit of their being detached from the link plates at the ends of the top chords.

    This was carried out by means of a special frictional gripping device attached to the cables some 20 feet behind the arch, and then by pulling on this grip with the 25-ton crane through a heavy block-and-tackle purchase, and working in conjunction with the hydraulic jacks, the cable bolts being released from the link pins, and the cables were allowed to slide back until the socketed ends rested against the pylon saddles.

    When this operation was completed at one set of link plates, there was practically no tension at the other end of each cable, which was removed from the link plates and run down to the pylon saddle by means of a light electrically-driven winch.

    Whilst the cables were being disconnected from the link plates, the erection of the centre posts, top chords, and top lateral bracing of the 14th panels was undertaken.

    During the erection of the half-arches the structure consisted of two cantilevers, in which the top chords were in tension. In order to withstand the high-tension erection stresses, the four vertical webs of the top chords of the first five panels were strengthened by means of additional plates attached thereto by specially fitted pins and bolts. The weight of this additional erection material was 798 tons.

    Before the final jacking operations were undertaken to change the arch from the three-hinged to the two-hinged condition, it was necessary for each member of the arch to have its final effective section, so that, while the cables were being disconnected, the pins and bolts connecting the temporary tension plates in the five end panels were driven out, so that the temporary erection material would not take any of the jacking stress.

    The arch was converted into the two-hinged condition by jacking the top chords apart at the centre top chord joiint.

    The permanent joint at the centre of each top chord consists essentially of four forged steel saddles enclosing two pins, each 10 inches in diameter. The saddles and pins were hung in the gap between the chords in a special frame before the four hydraulic and eight screw-jacks were assembled. As the force was applied by the hydraulic jacks, the screw jacks were made to follow up the motion, as the gap between end plates of the chords opened out. The difference between the overall width of the permanent saddles and pins, and the distance between end plates of the two chords after jacking, was to be made up by parallel fitted filler packs measured off and machined out of forgings provided for the purpose.

    The calculated thrust depended upon the elasticity of the structure, the loads upon it, and the temperature of the structure. The members of the arch had to be brought into their proper elastic condition, and to effect this the temporary reinforcing plates in the first five panels of the top chords on each side were disconnected; as the cables were being removed, the tension in the chords was relieved sufficiently to allow this to be done.

    The cables were removed as rapidly as possible, careful note was made of the load imposed on the structure by the erection equipment, and thermometer stations had been established at twenty-four points throughout the structure. Meanwhile the jacking equipment was assembled in the space between the ends of the top chords at the centre.

    This consisted of four hydraulic jacks, each 950 tons capacity, two operating near the top and two near the bottom flange of each top chord. Each jack was made of 3 per cent. nickel steel, 2½ inches thick, and worked at a pressure up to 4 tons per square inch. Two screw jacks were placed alongside each hydraulic jack to follow up the movements of the latter, eight hydraulic and sixteen screw jacks being employed in all for the jacking. The screw jack consisted of a central cylinder into which left and right hand buttress threaded rams were screwed. By rotating the central cylinder with capstan bars, the required movements were obtained. The hydraulic pressure on each truss was supplied from two hand-operated pumps with the necessary gauges. Each jack and gauge had been calibrated in the 1,250-ton testing machine provided by the contractors under the specification for testing model members for the bridge.

    On Monday, 8th September, the cables had been all removed except 37 on the southern side and 15 on the northern side, and some of these were hanging slack. The day was cloudy and extraordinarily well suited for the performance of the final jacking operation, on account of the equable temperature and the extremely small variations in the temperature of the various members of the structure as indicated by the 24 thermometers. It was accordingly decided to perform the jacking before the remaining cables were released, as the possible error involved in the calculation of the effect of the weight of the cables was less than that which would have been caused in determining the mean temperature and its effect had no such perfect temperature conditions prevailed. The jacking force as calculated for a temperature of 60.5 degrees Fahrenheit was 3,272 tons per truss, corrected by — 22 tons for the cable effect, and so at 5.15 p.m. the 3,250 tons force was applied by the jacks to each arch truss.

    During the operation the chords were forced apart a total distance of about 5¼ inches. The total gap on completion of the jacking was 299/16 inches on the eastern truss, 2925/32 inches on the western truss. The space occupied by the saddles was filled with fitted packs in pairs. These were machined to size, and on the morning of 10th September the packs were fitted in position, the load on the jacks released, and the jacks removed.

    From the time the lower chords met on the 8-inch pins until the top chords were jacked up and all cables removed, the centre of the lower chord rose upward a distance of 1 foot 1½ inches, the elevation of the centre pins at a temperature of 65 degrees Fahrenheit being 349 feet 7½ inches above the level of main bearing pin. With total dead load the structure should assume its geometrical form; the elevation of the lower chord centre joint should be 350 feet above the level of the main pins at a temperature of 72 degrees Fahrenheit.

    The work of suspending the deck from the arch trusses proceeded rapidly and, except for odds and ends, is now completed, and the northern half covered with coke concrete.

    During the last week in June, 1931, the last footway span between the pylon and the main span on the south-west corner was erected. This lift constituted the last bridge member, excluding overhead wiring brackets, chord footways, manhole covers, &c., to be erected in position.

    On the 27th June the 25-ton cranes which were erected for dismantling the creeper cranes were taken down.

    From the foregoing it will be seen that the following operations were carried out during the year: —

    (1) The remaining five panels of the arch were erected.
    (2) The half arches wore lowered to close on the pins.
    (3) The conversion from the three-hinged to the two-hinged condition was effected.
    (4) The whole of the hangers and all of the steelwork for the deck suspended from the hangers were erected as the creeper cranes receded.
    (5) The anchorage cables were detached from the arch and removed from the anchorage tunnels.
    (6) The pylon saddles were dismantled and taken down.
    (7) The 798 tons of temporary reinforcing plates were removed from the first five panels of the top chords.
    (8) The creeper cranes were dismantled and removed to the workshops.
    (9) The main painting gantry and six auxiliary gantries were erected in position beneath the deck of the main span.
    (10) The pylon stairways in the north and south pylons were erected to the 155.50 level.
    (11) The overhead wiring structures on the approach spans were erected in position.

    A total of 13,067 tons of steelwork was erected during the year.

    During the year 294 tons of rivets were delivered, making the total rivet deliveries 2,719 tons.

    The attached diagram shows the progress of construction at each three-monthly period since 30th September, 1926.

    (d) Painting.

    During the year the application of the first field coat was completed on the north and south approach spans and on the main span excepting for the outside surfaces and the inner floors of the upper and lower chords together with the lower portions of the cross girders of the dock; these lower portions being left to be painted from the painting gantries.

    A start was made with the application of the finishing coat during October, 1930, on the northern approach spans, and during the year practically the whole of the northern approach spans received the finishing coat excepting for the roadway and footway parapets and handrailing.

    Work is still proceeding with the application of the finishing coat on the southern approach spans and is now three-parts complete.

    During the year there were delivered: —

    4,160 gallons of shop paint,
    3,119 gallons of 1st field coat,
    4,375 gallons of 2nd field coat,

    making the total deliveries to date:

    15,920 gallons of shop paint,
    6,243 gallons of 1st field coat,
    4,375 gallons of 2nd field coat.


    The general remarks dealing with the northern approach apply also to the southern approach.

    (a) Excavation.

    The crescent subways excavation, grading the bridge highway, and the various regradings of the approaches constitute the main activities under this heading.

    A total of 39,934 cubic yards were excavated. All the spoil was dumped in position as arch backfill, embankment viaduct, &c.

    In addition, a considerable quantity of spoil was obtained from the City Railway Construction.

    (b) Concrete Work.

    During the year, 31,162 cubic yards of concrete were placed, of which 12,459 cubic yards were plain concrete, the balance being reinforced concrete. The principal items were the flat top construction, including walls and floor, Argyle-street arch, and the 70-feet arch at the end of Contract.

    (c) Waterproofing.

    A considerable quantity of waterproofing was carried out, there being 8,541 square yards of mastic, both horizontal and vertical, and 7,649 square yards of bituminous sheeting laid during the year. To protect this waterproofing material and the- balance of that laid previously 19,116 square yards of brickwork were laid, equivalent to 1,975 cubic yards of brickwork.

    (d) Brickwork.

    Various retaining walls were carried out in brickwork, the total amount being 1,124 cubic yards.

    Sydney Harbour Bridge Rate Levy—Payments and Outstanding Amounts at 30th June, 1931

    Sydney Harbour Bridge – Expenditure to 30 June, 1931.

    (e) Steelwork.

    During the year 389 tons of steelwork were placed, being principally broad flange beams and rolled steel joists in the flat top construction and pedestrian subway at Argyle-street.

    (f) Plastering.

    A commencement was made with the plastering work and at the end of June over 600 feet of the west retaining wall parapet and about 120 feet of that of the east retaining wall had been plastered.

    (g) General.

    Considerable progress was made with placing the reinforced concrete racks for the signal and electrical engineers' equipment, in all 3,660 feet being completed.

    In the vicinity of Scots Church an area of widened York-street was penetrated to act as a temporary surfacing until the backfilling over the tunnels has settled.

    The area penetrated was 1,420 square yards. The area of tar dressed footways carried out in the same locality was 348 square yards.

    Demolition of several buildings in Kent-street between Gas Lane and Napoleon-street took place so that the street could be widened. The Grafton Bond and Noyes Bros, buildings were being cut back by the Building Construction Branch to the new alignment.

    In addition, there was considerable fencing erected, and services temporarily and permanently deviated.

                    4. FINANCIAL REVIEW.

    (a) Land Tax.

    To defray one third of the capital cost of the construction and land resumptions and provide for the maintenance and lighting of the roadways and footways of the Sydney Harbour Bridge and Approaches from Waverton Station on the northern side of the Harbour to Wynyard Station on the southern side, a land tax of one half-penny in the pound was imposed upon the Unimproved Capital Value of all rateable land within the City of Sydney, the Municipalities of North Sydney, Mosman, Manly, Lane Cove, Ku-ring-gai and Willoughby, the Shire of Warringah and portion of the Shire of Hornsby.

    The tax was first imposed in 1923, the details of the rate levy for the years 1923-31 are as shown on the table attached. Of the total of £1,481,320 7s. 1d. due to 30th June, 1931, a total of £1,280,505 13s. 4d. had been received and paid into the Special Deposit Fund, leaving a balance of £200,814 13s. 9d. to be paid before 31st December, 1931.

PWD 1931 Photo 1.JPG

    The table adjacent shows the details of rates due since the tax was first imposed, the payments to 30th June, 1930, and the balance outstanding at that date.

    (b) Expenditure.

    The total expenditure to 30th June, 1931, is shown in the table adjacent. The cost to date of the Bridge and Approaches, including land resumptions, accrued interest and all other charges, is £8,136,946 10s. 4d., of which interest on expenditure is £1,048,931 17s. 3d., and resumptions £1,252,258 0s. 2d. Had it not been for the financial crisis it had been expected that the major portion, if not the whole, of the cost of the resumptions would be recouped by the sale of the residues, but this cannot be hoped for at present, and therefore the most advantageous course seems to be to hold the residues for a few years and then place them on the market.

    For the Contract of Dorman, Long and Co. Ltd. wages variations due to alterations of awards and the introduction of the shorter working week and the excess overhead consequent thereon has risen to almost 14 per cent, of the total payment. This percentage is higher than previously on account of the greater margin above ordinary award wages due to men being engaged upon the main span.

                    5. STAFF.

    The number of men employed on the Sydney Harbour Bridge and Approaches, excluding subsidiary contracts, at 30th June, 1931, was 1,509, employed as under: —

    Approaches—Public Works Department 893
    Civil Engineering 174
    Painters 66
    Workshops at Milson's Point 83
    Erection of Steelwork 125
    Moruya Quarry 168
    Total 1,509

Graph showing the quantities of steelwork delivered, fabricated, erected in place, and completely riveted in place since the first steel delivery.

Diagram showing the progress of construction at each three-monthly period.

    I again wish to express my appreciation of the excellent manner in which the staff of the Sydney Harbour Bridge Branch have carried out their duties during the past year.

                    J. J. C. BRADFIELD,

                    Chief Engineer,

                    Sydney Harbour Bridge.

                    23rd October, 1931.

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