The Bridge
►
The Quebec Bridge collapsed on the 29th of August 1907.
►
It was to span 550m across the St Laurence River.
►
The bridge was designed as a cantilever bridge.
►
Difficulties were noted in riveting the bottom chord splices, due to
deformation of the faced ends of the middle ribs.
The Bridge
►
These deformations were ignored and construction continued.
►
The central, suspended span began to be constructed in July.
►
Early August the end details of the lower compression chords began
to show signs of buckling.
The Bridge
►
6th August: two of the lower chords of the south arm cantilever were
bent
►
12th August: the splice between two lower chords was also bent.
►
27th august:A chord of the south anchor arm, which had showed a
deflection of 1.5cm only a week before, showed a deflection of 5cm.
►
On the 29th of August two of the compression chords on the south
anchor arm suddenly failed.
►
This failure spread through the south anchor of the bridge and eventually to
the partially constructed central span
►
Within 15 minutes the entire superstructure had collapsed into the river
beneath
Design of Bridge
►
The design of the bridge was quite a difficult one due its location.
►
As the St Laurence was a shipping lane the Quebec Bridge required
a single span of approx. 500m and height above the river of 45m
Design of Bridge
►
Along with a 22m width required to accommodate railway tracks,
streetcar tracks and two roadways led to a particularly large and
heavy central span.
►
In the case of any cantilever bridge the weight of the central span is
key to the design.
►
Steel plate cylinders were to be used as the main compression
members. These were to be prefabricated off site.
Technical Factors in the Collapse
►
Cooper (Chief Engineer), recommended that the span be increased to
550m.
►
This was to speed up construction and prevent piers being subject to
heavy ice flows during winter
►
The main factor responsible for the failure was an incorrect initial
calculation of the weight of the bridge
►
Construction was started assuming the initial estimated weights were
correct.
Technical Factors in the Collapse
►
The bridges actual weight was almost 3 million kilograms greater
than the design value.
►
It was decided that this excess weight was catered for in the safety
tolerances.
►
During the construction phase inadequate riveting of some of the
bridges key weight bearing lower chord members in the south
anchor left some key elements unstable.
►
This was at least partially due to lack of understanding of the
instability of latticed compress ional members during construction,
i.e. asymmetries during construction lead to increased likelihood of
failure.
►
Finally the lack of action taken when deformations far exceeded
expected values was a big contributor to the final disaster
Human Factors in the Collapse
►
Theodore Cooper, was appointed as chief consulting engineer in 1900.
►
He had signalled that the Quebec Bridge would be his final project.
►
Pride in this project inhibited the appointment of a second consultant
engineer to review technical aspects of the design and in particular the
high unit stresses in the bridge members.
Human Factors in the Collapse
►
The appointment of the Phoenix Bridge Company has been questioned
since the disaster.
►
Pressure was brought to bear on Theodore Cooper, the consultant
engineer, to accept their tender.
►
No tests had been done to revise the weights under the new
specifications drawn up by Cooper to compensate for the increased
bridge length.
►
Work went ahead using outdated assumed weights.
►
Cooper did not intervene, he accepted the theoretical figures provided
by the Phoenix Bridge Company.
Human Factors in the Collapse
►
Construction went ahead using proposal drawings only. These were
approximations and the design was as yet incomplete.
►
During construction the Chief Consulting Engineer, Cooper, never
actually visited the construction sight.
►
He instead appointed a recently graduated inexperienced engineer,
Norman McLure, to oversee the construction.
►
The distances involved made communications slow in emergencies.
Lessons Learned
►
Key to a successful construction
project is ensuring sufficient
funds are in place to see the
project through.
►
If the tenders do not meet the
specifications in terms of cost
then the project should be reassessed and a revised tender
issued.
Lessons Learned
►
It is extremely important to have a concrete set of design drawings
available at the outset of a project.
►
The Quebec Bridge Disaster prompted research into the
understanding of latticed compression members in a major bridge
structure, as there was little understanding beforehand
►
It is important to have more than one means of checking design
drawings and construction details.
►
The design principles of smaller scale bridges cannot be applied to
larger scale bridges
►
It exposed the importance of the Chief Consulting Engineer being
present on site.