The story of Quebec Bridge is a story of triumph after disaster. On two occasions thousands of tons of steel collapsed and fell into the deep water. Undaunted, those in charge persevered and completed an invaluable link in transcontinental communications
PREPARING TO RAISE THE CENTRAL SPAN of Quebec Bridge. While the enormous cantilever arms of the bridge were being built, the central span was being assembled at Sillery Cove, about miles away. The span was 640 feet long and the arched sides were 110 feet high in the middle. The span was floated to the site on massive steel pontoons.
THE building of the magnificent Quebec Bridge, which spans the St. Lawrence River near the capital city of the Province of Quebec, was a triumph after two disasters. About seventeen years elapsed between the time when the engineers began work and the day when the 5,100-tons central span was hoisted into place 150 feet above the great river. In the interval there had been two serious accidents that had shocked Canada. The story of the bridge is one of courageous perseverance that refused to be daunted by disaster. For years the bridge has been an inspiration to all who have seen their plans wrecked and need courage to try again.
Affording access to the Great Lakes, the St. Lawrence River is part of the waterways which extend for more than 2,000 miles into the heart of North America. The river was, however, a formidable obstacle to the engineers who wanted to bridge it to link Quebec with the eastern provinces of Canada. Schemes for bridging the river go back to 1853, when there was no bridge across the river at any point. The first bridge to span the St. Lawrence was Robert Stephenson’sVictoria Tubular Bridge at Montreal. This was opened for traffic in 1860.
The project for a bridge to link Quebec, on the north side of the river, with the south shore was revived in 1882 when a charter for a bridge was granted; but this project did not materialize. Definite progress was made in 1887 when the Quebec Bridge and Railway Company was incorporated. Years of consultation and investigation followed, and a design for a cantilever bridge was accepted from a New York engineer. In 1899 the contract for the bridge, to cost £2,000,000, was awarded to the Phoenix Bridge Company.
Preparations were made to build the bridge at a site where the banks of the river are about 200 feet high and the river is nearly 2,000 feet wide and 200 feet deep. To cross this formidable gulf it was proposed to build a cantilever bridge with a total length between abutments of 3,220 feet. The single deck, 150 feet wide and 150 feet above the water, was intended to accommodate a road and two footpaths, two tramway tracks for electric vehicles and two railway tracks. The two anchor spans were to be 503 feet long each and each of the two cantilever arms was to be 562 feet long, the gap between the two arms to be bridged by a central suspended span 675 feet long. The bridge would have an overall span from centre to centre of the two main piers of 1,800 feet, or 90 feet more than either of the two 1,710-feet spans of the Forth Bridge, its prototype. About 38,500 tons of steel were to be used.
Work was started on the substructure for the bridge in August 1900. The pier nearest the south shore of the St. Lawrence was completed and the building up of the south cantilever began. By the summer of 1907 the south anchor arm and about one-third of its cantilever span had been erected, the whole extending over the river for about 200 feet. One day it was noticed that the bottom, or compression chords of the anchor arm were bending slightly and this fact was reported. Work continued, however.
At 5.35 pm on August 29, 1907, shortly before the eighty-six men on the structure were due to cease work for the day, a grinding sound was heard. The compression chords crumpled, and in less than half a minute the 17,000 tons of steel collapsed, about half falling into the deep part of the river and the remainder crashing astride the pier and along the river bank in a dreadful tangle of plates and girders. The eighty-six men fell with the structure. Only eleven were saved. The crash was heard miles away in Quebec.
The news was flashed round the world and caused consternation and controversy. A Royal Commission set up by the Dominion Government reported that in its opinion the accident was due to errors in designing and building the bridge, the outcome of lack of practical knowledge of how to plan and prepare for a structure on such a scale.
But the need for a railway bridge at the site was growing. Such a bridge was a necessary link in the transcontinental line of the Canadian National Railways, of which the Government had undertaken to build the section between Moncton, N.B., and Winnipeg, Manitoba. The Government, therefore, decided to take the responsibility. When tenders were invited, engineering firms were allowed to submit alternative designs. Thirty-five tenders were submitted, and the design offered by the St. Lawrrence Bridge Company, which had been formed to combine the resources of the Canadian Bridge Company and of the Dominion Bridge Company, was accepted.
The successful design was for a cantilever bridge measuring 3,239 feet long and 88 feet wide. There were to be two approach spans, one of 150 feet and the other of 269 feet, two anchor arms each 515 feet long, two cantilever arms each 580 feet long, and a centre span of 610 feet, the length of the river span from centre to centre of the cantilever towers being 1,800 feet. There were to be two railway tracks and two footpaths. The company contracted for the steel superstructure. The contract for the substructure, which included the foundations for the piers and the erection of all the masonry was awarded to another Canadian company, Messrs. M. P. and J. T. Davis.
THE NORTHERN PIER of Quebec Bridge, with steelwork being prepared for the hoisting of the central span from floating pontoons. For building the pier an immense caisson was used, 180 feet long, 55 feet wide and 68 feet high. Excavation and sinking of the caisson were carried out continuously, day and night, and the caisson was filled with concrete at the rate of 1,000 cubic yards a day. The depth of the pier is 101 feet below high water and the vertical post of the tower resting on the pier is 310 feet high
The outstanding feature of the design was the new system of girder bracing known as the K truss, because of its similarity to the letter K. The truss was designed by Mr. Phelps Johnson. Before the design was accepted the K truss was compared with every other known system, and its strength, ease of erection, appearance and distribution of material turned the scales in its favour.
Workshops Specially Built
BEFORE building could begin in earnest the wreckage of the fallen bridge had to be cleared out of the way. Moreover, as there were no workshops in Canada at that period equal to the task of making the huge members required for the bridge, new engineering shops had to be built and equipped. The workshops were erected at Montreal. Extensive storage yards were laid out on both banks of the river at the site of the bridge. In these yards were railway tracks to enable 30-tons locomotive cranes to shift lighter material, overhead cranes of 83 feet span and of 70 tons lifting capacity being provided for heavier loads.
The dreadful half-minute crash in 1907 not only wrecked the work of years but also provided a big task for the demolition and salvage party which began work in December 1909. The thousands of tons of steel which fell into deep water were out of the way and offered no obstacle to navigation, but about 8,000 tons of the anchor span lay crumpled in a mass, 500 feet long and 80 feet wide, piled up to a height of 40 feet in places.
A team of twenty-five men tackled the tangle with dynamite and oxy-acetylene cutters, blowing up the heavier sections and then cutting them into pieces that could be transported. Sometimes the charges were placed in position at low water and fired when the tide had submerged them, to reduce the risk of injury from splinters of steel. Instances were reported of fragments being blown across the river to the opposite shore. About 5,000 tons of scrap metal were recovered m nine months and sent to Montreal to be sold.
While this demolition was in progress the problem of the piers was tackled. The piers for the original bridge were sound, but they were not in the position needed for the new bridge and their dimensions were not suitable; therefore they had to be demolished. It was decided to build the north pier first, and a large building of sectional timber was erected on the north bank in which to build the caisson for the pier on that side. This caisson was 180 feet long, 55 feet wide and 68 feet high. When it had been completed, the wooden building was dismantled and ferried across the river to the south bank and re-erected so that the caisson for the south pier could be built during the following winter. This caisson was slightly smaller than the first. Dredgers scooped out the two sites in the bed of the river.
When the caissons were ready they were launched. Each was floated into position and gradually lowered until the cutting edges bedded evenly. The caisson workers toiled in shifts so that drilling and sinking were continuous night and day. To save time the filling of the caissons with concrete proceeded simultaneously with the excavation and sinking, at the rate of 1,000 cubic yards of concrete a day.
Construction of the bridge was hampered by the fact that the severe winter climate restricted field work to the period from the end of April until early in December each year. To ensure that every available day could be used to advantage, every section of the enterprise - workshops at Montreal, transport to the yards at the site, and the erectors - had to work to schedule. The utmost care was taken to make the steel components exact to drawings, and they were carefully examined before they left the workshops to make sure that there should be no hitch at the site.
About 8,000 tons of steel were used to build the scaffolding, or falsework, to support the floor system and to aid in the construction of the bridge. Loco motive cranes were used to set the approach spans on their scaffolding, but the giants of the work were two erection “travellers”, steel mobile towers, one of which was built for each bank. Each tower was 210 feet high, 54 feet wide and 37 feet long. At the top were two electric cranes with 60-tons hoists, a transverse travel of about 14 feet, and a maximum working spread of 96 feet. At each of the four corners of the traveller was a 90-feet boom to hoist weights of up to 15 tons, and there were also 7-tons auxiliary gantry hoists for lighter loads. Each traveller, when equipped, weighed 940 tons, and was moved as required along a double set of rails.
When the 1914 season opened, the approach arm on the north bank was complete and ready for the traveller. This was moved into position along the rails to the anchor pier of the cantilever arm. It began erecting scaffolding and creeping outwards towards the .main pier upon which it set the grillages and shoes, and then worked back to the anchor pier. In a series of journeys it erected the lower chords of the anchor arm, and then the lower and upper triangles of the K trusses.
This part of the work was almost completed when winter set in and the river began to freeze from shore to shore, so the scaffolding and steelwork were protected from the ice and left until the spring of 1915. Then the anchor arm was completed, and the scaffolding was dismantled and ferried across to the south bank, where it was used to support the traveller working on the anchor arm on that bank. Meanwhile the north traveller began on the cantilever arm.
Towing 5,100 Tons of Steel
ALTHOUGH the men on the north bank had a good start, those on the south bank strove to eclipse them in setting steel. One day the southern team set 670 tons, the record for that year, compared with 387 tons - the highest on the northern side that season. By the close of the season the men on the south side had completed the anchor arm. Those on the opposite shore had completed the cantilever arm, which stretched over the St. Lawrence for a distance of 580 feet from the main pier. Work was concentrated on the cantilever arm for the south shore at the beginning of the 1916 season and was completed by September. The bridge was then ready to receive the centre span.
Work on the span had been meanwhile proceeding at Sillery Cove, 3½ miles away, and this was ready. The assembly of the span was, however, only one part of a series of operations. The mass of steel weighing 5,100 tons had still to be shifted to the bridge and hoisted 150 feet from the water. The span was 640 feet long and the height of the arched sides was 110 feet at the middle. The huge bulk had been assembled in the cove on scaffolding erected over the water.
The height of this falsework enabled six steel pontoons to be floated under it to receive the span. Each pontoon was 160 feet long, 32 feet wide and 11½ feet deep. It was fitted with valves and pumps so that water could be admitted or expelled as desired, enabling the vertical position to be adjusted in relation to the pontoon.
COMPRESSION CHORD of one of the cantilever arms being placed in position. It was the collapse of the compression chords of the first Quebec Bridge which caused 17,000 tons of steel to crash to destruction on August 29, 1907.
The plan was to use the flood tide, the cove being below the site of the bridge, to float the pontoons and their huge burden up to the bridge and to moor it ready for hoisting. As the tide had a flow of over six miles an hour and a rise of from 14 to 16 feet the timetable had to be worked out carefully with a margin to cover unforeseen delays. In addition there was the risk of an adverse wind affecting the tide and influencing the span.
Weather and tide were favourable on the morning of September 11, 1916, and the order to start was given. The six pontoons were floated in position, three on either end of the span. They were secured and took the weight evenly. Then a flotilla of tugs took charge, pulled the mighty tow into the stream and, with other tugs in reserve, towed the span towards the bridge. By skilful manoeuvring five tugs nursed the span nearer and nearer and then, with the aid of two more tugs, swung it neatly athwart the river beneath the extended tips of the two cantilever arms, ready for it to be made fast to the special mooring frames which hung down from the bridge.
These two mooring frames were independent of the hoisting gear. They were two large cantilevers hinged from the deck of each arm of the cantilevers of the bridge. The lower end of each was suspended over the water and could swing some distance to and fro, the ends being pulled backwards by wire ropes to give ample room to enable the ends of the span to be floated into position. When this had been done the wire ropes were slacked off by electrical gear on the bridge so that the frames hung vertically. Then the ends of the frames were secured to the ends of the span with wire ropes.
The hoisting gear was independent of the mooring frames. In brief, the plan was to pump compressed air from power houses on either bank to hydraulic jacks on each arm of the bridge. At the end of every 2-feet stroke these pumps lifted the girders from which were suspended chains. The chains were pinned in position while the lifting girders were lowered for another stroke and then repinned to the lifting girders for the next lift of 2 feet. Two girders at the bottom of the chains were fixed in position transversely under the ends of the span, each girder having two shoes which fitted each corner of the span.
The lifting chains were steel rods 28 feet long and 2 ft 4-in wide, connected by movable pins. Each rod had holes of 1 foot diameter, 6 feet apart, into which the pins fitted. There were eight of these chains, four to each cantilever, and these four were in two pairs, one pair for each corner of the cantilever. As the span was raised the tops of the rods of the chains projected above the top of the cantilever, but each rod could be removed as soon as the complete link was clear.
A heavy cross-girder, supported on rocker bearings, was set up at each corner of the cantilever arms, and from this other girders were suspended. The hydraulic jacks rested on one girder and on top of the plungers was a duplicate girder which was raised 2 feet by each stroke of the plunger. These two girders had holes 1 foot in diameter, set 2 feet apart, there being three holes vertically. The holes in the chains were 6 feet apart, but one pair of holes in the girders was always opposite a hole in the chain. This enabled the chain to be pinned to the fixed girder while the lifting girder was freed and lowered, when it was pinned to the chain for the next upward stroke.
There were separate control valves for each jack, and tell-tales to help the operators to keep the lifting girders square. Telephones linked the stations on either cantilever with the Engineer-in-Chief. As a safeguard in the event of the failure of the hydraulic jacks, screw-jacks were installed and manipulated to follow each stroke of the hydraulic jacks, so that they could take the weight and allow a hydraulic jack to be removed and repaired. The suspension and lifting appliances added several hundred tons to the weight of the span, bringing the total weight to about 5,540 tons. Everything had been calculated for - even a delay - for there were holes at the bottom of the chains to enable the span to be shifted lower if the tide fell before its time or there was any delay, so that the weight need not be taken prematurely by the jacks.
Everything went without a hitch. The span was transferred to the lifting gear, the tugs unmoored and steamed a short distance away, the pontoons still bearing the weight of the span. The crowds on the shores and the watchers on board the craft waited and watched in silence as the order to begin hoisting was given. Then the jacks began the first lift, and the span rose clear from the pontoons, which drifted away on the tide.
THE COLLAPSE OF THE CENTRAL SPAN in September 1916. Having been assembled elsewhere and floated to the site on steel pontoons, the 640-feet span was being raised, 2 feet at a time, by hydraulic jacks and lifting chains to the level of the cantilever arms, 150 feet above the water. When the span had been raised 30 feet, however, it collapsed and its 5,100 tons of steel fell into the deep river.
Every craft blew her siren. The crowd cheered. The crucial moment had passed and the span was beginning its upward journey. Methodically, the sequence of each cycle of operations to raise the span one lift of 2 feet went on until the span was some 30 feet above the water, and the order was given for the men to stop for rest and a meal. They came back and resumed work. One lift was accomplished.
Suddenly a cracking sound was heard from one corner of the southern end of the span. The corner broke away and began to twist under its own weight until it touched the water. It continued to twist until that end was nearly vertical while the far end of the span was horizontal. For a few seconds there seemed a hope that the span would not snap, but then there came a succession of reports, and the southern end of the span broke away and dragged the other end with it, falling into the river with a tremendous splash.
An inquiry led to the belief that the accident was caused by the collapse of a steel casting forming part of the rocker bearing under the south-west corner of the span. Thorough tests showed that the mooring cantilevers and hoisting chains were not at fault. The great anxiety was whether the shock of the sudden release of more than 5,000 tons had damaged the bridge, but a thorough examination disclosed no sign of damage.
The span had fallen into the deepest part of the river, which had swallowed part of the previous bridge. New steel was ordered and, despite difficulties due to the war of 1914-18, the bulk of this was delivered to the workshops' by the end of 1916 and fabrication of a new span was started. In the spring of 1917 assembly began at Sillery Cove. A suggestion was made that the span should be erected on top of a huge floating tower at a height of 150 feet, and that this should be towed to the bridge, but the question of windage and other problems caused this suggestion to be dropped. It was decided to persevere with the method tried before. As a safeguard, new hoisting chains and equipment were provided, and a few alterations were made.
Almost exactly a year after the accident the new span set out on September 17, 1917, for its short but hazardous voyage to the bridge. Once again the tugmasters did their work excellently. The span was moored and the first lift of 2 feet was made, This time every step was taken with great deliberation, and no attempt was made to hoist the span rapidly. Twelve lifts were made on the first day, twenty-two on the second and twenty-six on the third.
THAT night the span was left 120 feet above the water, with a further 30 feet to climb; but the weather became threatening and the wind increased to a speed of thirty-five miles an hour. The wind was still blowing strongly on the morning of the fourth day, and the engineers were doubtful if hoisting could be resumed. Anxiously, the mooring ropes were slacked, so that the effect of the wind on the span could be observed ; but it was only slight, and the order to resume work was given after the tackle had been tightened to prevent any lateral movement of the span.
As the span moved steadily upwards the permanent suspension bars were prepared. Shortly after 3 p.m. the span was hoisted, and by 4 o’clock was connected to each cantilever arm, and all the connecting pins were secure. In the following weeks the floor of the span was placed in position, and by the end of the year the bridge was opened for railway traffic. A little while later the footpaths were completed for pedestrians and the bridge was painted.
The cantilever span of 1,800 feet is the longest of its type in the world. The total weight of the nickel steel used was 66,480 tons.
There are 14,900 tons of steel in each anchor arm, exclusive of the floor carrying the railway, and 10,430 tons in each cantilever. The tops of the vertical posts on the two main towers are 310 feet above the piers, and the trusses taper to a depth of 70 feet at the cantilever and anchor arms. The depth of the main piers below high water is 101 feet. Nearly 3,000,000 rivets were used. The cost was about £3,000,000. In 1929 a 16-feet concrete road for motor vehicles was added to the bridge at a cost of £100,000. The job of painting the 210 acres of steelwork generally occupies thirty-five men for three years, during which they spray 7,800 gallons of paint.
The bridge connects the lines of the Canadian National Railways north and south of the St. Lawrence. It has shortened the railway route between Halifax and Winnipeg by 200 miles, and has provided the shortest connexion between the pulp mills and forests of Northern Quebec and the markets in the United States. It is the first bridge under which ships pass on their way from the sea to Montreal and other ports, and provides a thrill for liner passengers, as at first they wonder if the masts of the ship will be able to pass under the bridge.
THE LONGEST CANTILEVER SPAN IN THE WORLD is that of Quebec Bridge. The span is 1,800 feet, 90 feet longer than either of the two main spans of the Forth Bridge. The ice caused work on the structure to be suspended yearly between December and April.
[From part 44 and part 45, published 28 December 1937 and 4 January 1938]