Historical notes on Hamilton Railway Bridge.

(By A. S. Wansbrough , M.Inst.C.E., Designing Engineer, New Zealand Railways.)

The Hamilton Railway Bridge, in 1906.

The Railway bridge over the Waikato River at Hamilton was designed in 1880 in the office of the late Mr. John Blackett, M.Inst.C.E., Chief Engineer for the North Island. Mr. Blackett came to New Zealand in 1851, entering the service of the General Government of New Zealand in 1870, and becoming Chief Engineer for the North Island in 1878, in which capacity he let the contract for the bridge. In 1884, he became Engineer-in-Chief for the Colony.

The original bridge was of three pin-jointed Warren deck girder spans of steel, each 132 feet long and continuous over two cast iron cylinder piers and supported at the ends on massive concrete piers. At each of the shore ends of the main spans were two 20 feet timber built-beam spans. The cylinders were 7 feet diameter, the pair nearest the Hamilton side being 160 feet long, and the pair nearest the Claudelands side 136 feet long. The respective depths below rail level would be 181 ft. and 157 ft., and depth below the river bed 78 feet and 54 feet respectively. The bridge was designed for a combined live and dead load of I 3/4 tons per foot, giving very little margin over the weight of the locomotives then running.

The first contract for the construction of the bridge was let on 3rd November, 1881, to W. Sims, for £5,519, but nothing was done and the contract was terminated. On 18th September, 1882, a new contract was let to J. R. Stone for £4,312/13/6, exclusive of the casting of the cylinders. These were supplied by A. & G. Price, of Thames, the contract price being £1,376. The bridge was completed about the end of July, 1883, but was not brought into use until the opening of the Hamilton-Morrinsville railway on 1st October, 1884. The line to Cambridge was opened a week later.

The bridge was tested by the late Mr. John Coom, M.Inst.C.E., Resident Engineer at Auckland for the newly constituted Working Railways Department, on 5th December, 1884. A class F engine, and a class L engine coupled together, a total load of 40 ½ tons distributed over 40 feet, were placed on the centre of each span in turn. The deflection was about ¼ inch on each span, the effect of the continuity being noticeable in the adjoining span rising about one-sixteenth of an inch at the centre in each case.

(Hugh Bennett, photo.)
A. typical suburban train on the New Zealand Railways. Locomotive No. 767 (WAB Class) with an Auckland-Waitakere train at Morningside station, North Island, New Zealand.

The load was then increased to 117 tons on 123 feet by attaching to the locomotives three pairs of timber trollies loaded with rails. The deflection was from ½ inch to 5/8 inch, and this train was passed over the bridge at 10 or 12 miles per hour without appreciably increasing the deflection. Both Mr. Coom and Mr. F. W. Mac-Lean, M.Inst.C.E., who was associated with him on that occasion, later rose to the position of Chief Engineer to the New Zealand Railway Department.

The F and L class of tank engines, approximately 20 tons each, were the heaviest engines in use at that time in the Auckland district, which was then an isolated section. No example of the original L class engine is now in existence, but there are still several F engines in use for shunting purposes only. The heaviest axle load of any engine in use on the Auckland section at that time was 7 tons, and the designers of the bridges of that day did not think it necessary to design for any heavier loading, not visualising the remarkable expansion of railway development in the next fifty-years. A bridge of this class would to-day be designed for 18 tons axle loads.

There was no footbridge over the original bridge, but planks laid down the centre for the convenience of Railway page 28 page 29 Maintenance workmen soon encouraged trespass by pedestrians, and the Resident Engineer had difficulty in preventing it. In May, 1887, he reported: “The Town Clerk, although I have written to him, still persists in crossing. Shall I take legal proceedings?” and received the reply, “Yes, prosecute trespassers on Hamilton bridge at once.” There is no record of what dire penalties were visited on the Town Clerk, but perhaps the Royal clemency was extended to him on the occasion of Queen Victoria's Jubilee the same month! The planking was removed, but still the more venturesome attempted to cross, but as there was no close sleepering as at present the procedure was very risky, and it was quite common for the pedestrian to finish the crossing on hands and knees.

The opening of the Rotorua line in 1894 called for heavier engines to cope with the through traffic, and in 1902 the N class engines were brought up from the south. These were tender engines, six-coupled, weighing 45 ½ tons including tender, in working trim. The tenders had to be lightened, the overall length increased by putting in a false headstock, and the speed kept down to 10 miles per hour to keep the engines within the capacity of the bridge. The strengthening of the structure began to be contemplated as early as 1898. The Railway Department would not allow a footway to be constructed on the bridge until it should be strengthened.

In 1900 the Hamilton Burgesses’ Association carried without dissent a resolution “that the Government be asked to construct a road for foot passengers on the Hamilton Railway bridge when carrying out the contemplated improvements to the structure.” The Minister replied that “when this bridge is re-constructed a footway will be constructed. It is not, however, intended to put the work in hand for some considerable time yet.” Similar answers were given to further requests from the Mayor of Hamilton, the Chairman of the Kirikiriroa Road Board, and the Claudelands residents. A deputation waited on Sir Joseph Ward in 1902, who advised the Council to go in for an independent suspension bridge, estimated to cost £850. A deputation to Mr. Seddon in 1903 reminded him of Sir Joseph Ward's promise, but Mr. Seddon, after reading the letter produced, “smilingly remarked that the letter was very diplomatic, and that his colleague had not committed himself very deeply.” He added that he believed in the old French proverb, “Heaven helps those who help themselves.”

The opening of the Waihi line in 1905, and the Taupo Timber Company's private line made the strengthening of the railway bridge an urgent necessity, and early the following year plans were prepared for the work, to be spread over the next two years. The Waikato County Council agreed to pay £500 for the construction of a footway on the strengthened bridge, and £25 per annum for maintenance. The £500 was ultimately paid, however, by the Roads Department.

The accompanying photograph, taken in 1906 just prior to the strengthening of the bridge, shows the bridge of two girders on two cylinders to each pier, with no footway and the sleepers wide-spaced. It also shows the sparseness of settlement on the Claudelands side and gives some indication of the expansion of the town in the subsequent thirty years.

Plans were complete in 1906 for strengthening the bridge by adding a third cylinder and a third girder, the railway being shifted to the centre of the three girders, over which the load was distributed by long steel cross-girders. The built-beam shore spans were replaced with steel plate girders. A contract was let for the cylinders on 14th September, 1906, to S. Luke & Co., Wellington, for £2,354, and one for the fabrication of the superstructure on 8th January, 1907, to A. & T. Burt, Limited, Dunedin, for £5,872, the erection to be carried out by the Railway Department.

The decking was completely renewed in jarrah in 1920, and in 1932 another renewal was contemplated.

District Engineer's and New Works Staff, Wellington.—Back Row (Left to Right): Messrs. E. O. Moore, D. S. Woodley, W. G. Tiller, W. C. S. Tilsley, F. R. W. Green, J. Young, E. V. Friend, E. H. Lovatt, H. J. Heron. Middle Row: J. G. Tandy, N. O. Russell, B. P. Dillon, G. Shrimpton, J. M. A. Devlin, A. E. Shaw, K. H. Le May, W. G. Keating, R. A. McDougall, T. Duignan, E. R. Willkinson. Front Row: H. H. Thompson (Foreman of Works), W. E. Puddy (Assistant Engineer), T. A. Anderson (Assistant Engineer), R. H. Lovatt (Assistant District Engineer), H. L. P. Smith (District Engineer), W. B. Lee (Chief Clerk), C. H. M. Hawk (First Assistant Engineer), B. Tangney (Second Clerk), J. Brough (Inspector Permanent Way). Absentees: E. R. Williams, T. A. Harrison, A. C. E. Rippon, W. J. Dunlevey, E. W. Chesterman, A. A. Walker, E. M. Simpson.

At the same time a further strengthening of the main structure became necessary to carry the new K class locomotives weighing 135 tons with 15 tons axle loads, and renewal of the decking was held over pending the larger works. In 1934, Mr. R. Worley, A.M.Inst.C.E., Borough Engineer, submitted an attractive design for a new footway in steel, of electrically welded construction. The footway, which consisted of 14 feet 8 inch spans supported on the cross girders and main rail beams, was fabricated by the Borough staff and inserted in place by the Railway staff as the work of strengthening proceeded. The deck consisted of a bituinastic surface carried on a steel plate. The Council agreed to pay the Department £105 for the extra work due to the presence of the footway, to lay and maintain the asphaltic surface, paint the completed footway and maintain the footway in lieu of the previous annual payment.

The strengthening of the bridge consisted in the are welding of flange plates on top chords, cross girders, and main rail beams, while the pin joints were strengthened by welding on plates uniting adjacent lower chord members in such a way as to relieve the pins of part of the load. This work was completed in May of the present year. The whole superstructure is now of steel except the subsidiary rail beams of 12 inches by 9 inches ironbark. The total cost of the strengthening was £5,200, and with the one exception of the Makohine Viaduct the bridge is the most notable example in the Dominion of the strengthening of a large steel structure by electric welding.