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giving the wire the same curve it would have in its proper position. The wires were next drawn across the opening, with plummet attached, brought to the same sag and made fast. This was done on a calm night, and proved an accurate means of setting these columns.

The cribs for piers Nos. 4 and 5 were built larger than the rest, being 51 x 30 feet outside measurement. Shears had been erected on the last crib for handling the sections. Through some accidental cause a portion of the ballast had fallen into the voids of this crib reserved for the columns and it became necessary to employ a diving crew to remove them. With this exception, the operation of setting the bottom sections as previously described was performed for each of the piers.

The time of setting these sections was as follows:

Pier No. 1, July 19th,

1887

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Two periods of low tide were generally sufficient for setting these sections. The first tide was sufficient for a pair of them to be lowered, and they were secured and centred at the next.

The foundations by this time were all ready for the iron men to proceed with their work of completing the columns and connecting the sway bracing; but owing to unfortunate delays caused by unforeseen difficulties, the remainder of the iron did not arrive on the ground until late in the fall. The process of building on the sections proceeded with energy; the sway bracing was connected, and concrete filling followed on as fast as each section was rivetted. Cold weather suddenly came, and with it a run of ice in the river. Piers Nos. 1, 2 and 3 had been completed and filled with concrete up to high water, pier No. 4 partially finished, but pier No. 5 had to be abandoned without any bracing or concrete filling, above low water. Urgent efforts were made to get these finished, but with the river now almost blocked with floating ice, the men's lives were in danger, and the work had to be left, not, however, till the 50 feet span had been swung, and two sets of false work for the next span had been carried away. Attempts to get the sheathing in place failed, but some additional protection of round timber had been built around the cylinders.

The columus were now left in a seemingly precarious condition, without the trusses to stiffen them longitudinally, the cross bracing exposed to heavy ice floes, which could strike them obliquely with the force of

the rushing tide, and some of them only partially filled with concrete, or not at all.

The winter months passed, and the proverbial oldest inhabitant failed to recollect larger or more continuous floes of heavy ice than the Avon river experienced during that time. When spring came, it was found that pier No. 4 had experienced some dents above the concrete filling, and one of the tie rods was broken. Pier No. 5, which had no bracing or concrete filling, was partially demolished, the rest stood firm and perfectly true. This might fairly be considered a pretty severe test, and a sufficient answer to much adverse criticism on the adaptability of such a structure for the Avon River.

Operations were resumed in the month of May, and prosecuted to completion. The injuries to the columns had been repaired, the missing plates replaced and filled to the top with concrete. The work proceeded with rapidity, and the last span was swung in the first week in July. Soon afterwards the bridge was opened for traffic.

The superstructure is the ordinary type of American pin-connected Pratt truss with an ornamental iron lattice hand railing on each side. The specifications were the same as generally adopted under the Nova Scotia Bridge Act for iron bridges, with special clauses and modifications to suit this particular case, and as they would present nothing new it will not be necessary to reproduce them here, beyond a few of the principal requirements.

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Rolling load 1,350 lbs. per lineal foot, or 75 lbs. per square foot of roadway.

Ultimate tensile strength of iron at least 50,000 lbs. per square inch, an elastic limit not less than 26,000 lbs. per square inch, and a minimum elongation of 20 per cent. in 8 inches. Tensile strain produced in any member not to exceed 10,000 lbs. per square inch. Working

strain reduced on counters, hip verticals and beam hangers. Working compressive strain not to exceed 8,000 lbs. per square inch reduced by formula.

The cylinders were to be put together in sections of not greater length than 8 feet of 3-in boiler plate hot rivetted, no screw bolts to be allowed in connecting the sections. On top of each pair of cylinders there were to be two rolled I beams, 12 inches in depth, 60 lbs. per foot each, with plates and stiffening T's to support trusses.

Considerable work was done on the approaches. The old abutment on the Windsor side was cut down to the foundation, and rebuilt. The floor in the approaches is supported by trestles resting on the old work at about high water level, and has a grade of 1 in 20.

The iron superstructure, together with the columns, was contract work, and was built by the Dominion Bridge Co., Engineers and Contractors, Montreal. The preparation of the found tions, cribwork, concrete filling, together with the work on the approaches, was all performed by day work, under Government superintendence.

Supplying material, such as sand, gravel, stone and timber, was generally let by contract, the contractor delivering the material at the bridge site as required.

A contract was also let for building additional cribwork around the cylinders up to within 26 feet of floor.

TOTAL COST OF WORK.

Erection of iron superstructure and columns......$32190
Substructure (days work)....................

16395

Sheathing cribs and removing old piers (contract) 1760

$50345

In looking at the cost of this work, it must be remembered that the circumstances here were anything but favorable to making a good showing with a crew of men in a short, time. Men were at their post night and day, whenever the tide permitted, but could not work more than three hours at the most before having to make everything fast, and get ashore when the flood tide came. came. High wages had to be paid, as otherwise men could not be induced to work broken time in the wet and mud. Experienced foremen were employed, who ever kept a sharp look out for the safety of the men, as well as to see that each performed his full share of the work in a skilful and workmanlike manner, and it is a happy feature, that although the work was prosecuted at all hours

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of the day and night, in a dangerous locality, especially when the cold weather set in, not an accident or fatality occurred.

The bridge as now completed, is in general appearance, such as to satisfy the most sceptical, and is, to the casual observer, the most elegant structure of the kind in this province. To the eye of the engineer it is bold and strong, each detail being designed to add strength where it is most needed. The columns have a graceful and finished appearance, the workmanship is all that can be desired, and standing side by side with the English lattice railway bridge, the two bridges present striking examples of the European and American practice.

From the drawings accompanying this paper Plate XII has been prepared.

The author deserves the thanks of the members of the Society, for Mr. M. J. Butler. presenting an interesting description of a class of work that will be of more common occurrence as the country grows older and richer, viz. the substitution of steel and iron for wood. The building of permanent work in the place of temporary structures will no doubt follow rapidly now that iron and steel of excellent quality are being produced cheaply, whereas, with the decrease in quantity, the price of timber keeps steadily increasing.

The Town Lattice Bridge, when roofed over, was an excellent type of wooden bridge and gave great satisfaction. There is one of 80 feet span at Napanee, Ontario, which was built in 1840, and is still in good order, the timber being perfectly sound.

The type of pier selected for the Avon Bridge is one very much used in the Western States, where, owing to deep mud, it is often difficult to get good foundations, the practice being to drive piles and fill in with concrete. Of course the difficulty of getting good stone has a great deal to do with the adoption of iron and concrete piers.

It would seem, however, in the case under consideration, that it would be better to have had each pier in one piece, with ice breakers at each end in the shape of cutwaters, similar in form to those adopted for the pier of the New Hawksbury Bridge in New South Wales. The cost would have been very nearly the same, while there is no doubt that the single pier would be stronger and safer.

It seems to the writer a mistake to build such an important bridge, on a specification of 75 lbs. to the square foot of roadway, for the following reasons:

(1) All bridges are liable to the passage of heavy traction engines, concentrating from four to eight tons on two pair of wheels, seven feet centre to centre, to the passage of road rollers of the Aveling & Porter type, which weigh from ten to twelve tons, or to exceptionally heavy loads of machinery, stone, etc.

(2) The items that go to make up the cost of a bridge may be roughly divided as follows:

a. Raw Material, rolled plate iron 55 per cent.

b. Work on same in the shop

c. Transportation

d. False Works and erection

e. Profit and Administration

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