Quebec St Lawrence River Bridge
in Canada.
1899 Contract awarded to the Phoenix Bridge Co of Phoenixville, USA, to design and construct the steel cantilever bridge across the St Lawrence River.
1907 Engineering provided a detailed and well-illustrated description of the bridge over a period of eight issues. The unfinished bridge had already collapsed during this period. [1]
1907 'The two 1710-ft. spans of the magnificent Forth Bridge, so brilliantly created in the early days of steel construction, and so long of unapproached magnitude, lack 90 ft. of the length of the Quebec Bridge, and have less than half its capacity. That both great spans are cantilevers constitutes almost their only resemblance ; the Forth Bridge main truss members are all huge tubes, built up in situ, with elaborate plant established at the spot, and with all connections riveted, with consequent indeterminate stresses in some cases, notably at the feet of the main towers. The Quebec Bridge members have riveted rectangular webbed members for compression, and forged bars, not capable of transmitting compression, for tensile stresses. All primary joints are pin-connected, and all stresses are positive. All members were completely finished in the shops with highly - developed standard machine-tools used for the regular bridge business of the contractors, and all were erected as complete units, handled bodily, and supported in groups until successive panels were completed and self-sustaining.'[2]
1907 The south cantilever and anchor arm collapsed during construction. The bridge was demolished and the New Quebec Bridge was later built in its place.
1907 'Late in the afternoon of August 29 the entire completed superstructure collapsed almost instantly and fell to the ground, a total wreck, killing seventy-five of the eighty-six men at work on it, including all four of the erection foremen and the resident engineer. An experienced foreman on the false-work across the river was watching the men on the erecting traveller as they were making everything secure for the night preparatory to quitting in about fifteen minutes, he heard a loud noise like an explosion, and saw the end of the overhanging structure gradually descend until near the water’s edge, swaying a little up and down stream ; the traveller fell towards the centre of the river, the main posts collapsed, and the whole 17,000 tons of massive steel-work fell within a few seconds, probably about a half-minute after the first movement. The anchor-arm fell vertically and very nearly in the plane of its axis, on the dry land between the piers and partly over the main pier, where it is entirely accessible. The greater mass of the cantilever and suspended span, except a very small part of the first panel of the former, disappeared below the surface of the water, which, beyond the main pier, rapidly increases to a depth of over 200 ft., with a swift tidal current which precludes recovery or examination of any but a small portion of it. ....'[3]
A Royal Commission, headed by Henry Holgate, was appointed to determine the cause of the failure. The key finding of the Commission was that collapse resulted from the failure of the lower chords of the anchor-arm near the main pier, and that the failure of these chords was due to their defective design. P. L. Szlapka of the Phoenix Bridge Co was the designer responsible. The design was examined and approved by Theodore Cooper, consulting engineer of the Quebec Bridge and Railway Co.[4]
Engineering provided an editorial, based on a report published by the Engineering News.[5] It would be inappropriate to try to provide a precis here, but a few extracts may be of interest:-
'In the issue of October 31 last of the journal just mentioned is
published in full a transcript of Mr. Theodore
Cooper’s statements to the Commission, whilst in
that of November 28 we find an almost equally full
report of the evidence tendered by the officials of
the Phcenix Bridge Company.
Naturally, both statements are ex parte ; neither
was tested by cross- examination, and it is possible
that each party was less anxious to assume responsibility than would have been the case had the
bridge been brought to a successful conclusion.
But, even keeping these considerations in mind,
the impression left by the reading of these reports
is that a great responsibility rests on Mr. Cooper.
It was he, in the first place, who altered the span
from 1600 ft. to 1800 ft., rejecting the suggestion of
the Phoenix Bridge Company for a compromise of
1723 ft. The reason given for the alteration, which
in the natural course of things would have enormously increased the weight of the structure, was
the advisability of having the piers in the shallow
water near the banks, where they would be less
exposed to injury from the gigantic ice-shoves which
characterise the approach of spring on the St. Lawrence.
much force, but it is quite possible that it
backed, consciously or unconsciously, by a not unnatural desire on the part of Mr. Cooper for the
association of his name with the construction of
the largest span in the world. The increase in the
main span should, of course, have involved a great
augmentation in the cost and weight of the structure, and to bring the outlay within the limits
fixed by those responsible for financing the bridge
Mr. Cooper took the serious step of fixing the
maximum working stresses very high. ..... In America it has too often been a case of having
a cheap bridge or no bridge, and this would seem,
from the evidence of Mr. Cooper, to have been the
case here. Such economies as were practised were,
however, in the design rather than in the execution
of the work. There is a general agreement that the
materials and workmanship were good of their kind. .....'
The failed bridge was replaced by the New Quebec Bridge.
See Also
Sources of Information
- ↑ Engineering 1907/09/06 and 7 later issues.
- ↑ Engineering 1907/09/06
- ↑ Engineering 1907/09/20
- ↑ The Engineer 1908/03/27.
- ↑ Engineering 1907/12/13