In engineering practices, failures provide rare opportunities to learn the
skill to upgrade the technology in better
ways. A case of bridge failure is
discussed in the subject Article to provide the readers an occasion to learn
something extra for safeguarding the life of general public and for the
enhancement of technology.
At approximately 7:15 p.m.on the stormy night of 28 December 1879, the
central navigation spans of the Tay bridge collapsed into the Firth of
Tay at Dundee, taking with them a train, 6 carriages and 75 souls to
their fate. At the time, a gale estimated at force 10 to 11 was blowing
down the Tay estuary at right angles to the bridge. The
collapse of the
bridge, only opened 19 months and passed safe by the Board of Trade,
sent shock waves through the Victorian engineering profession and
general public. The
disaster is one of the most famous bridge failures
and to date it is still the worst structural engineering failure in the
British Isles. Detailed accounts of the disaster are given byPrebble
and Thomas. A more modern treatment, taking account of recent research,
is by Swinfen.
The first Tay rail bridge was completed in February 1878 to the design
of Thomas Bouch. Bouch was responsible for the design, construction and
maintenance of the
bridge. Most of his bridges were lattice girders supported on slender
cast iron columns braced with wrought iron struts and ties.The building
of the Tay bridge culminated in him being knighted. The Tay bridge was
nearly two miles long, consisting of 85 spans and at the time was the
longest bridge in the world. The spans carried a single rail track; 72
of these spans were supported on deck spans, the remaining 13
navigation spans were through girders. These "high girders", as they
were known, were 27 ft high with an 88 ft clearance above the high
water mark. It was these spans which fell. Most of the deck spans, all
of which remained standing, were transferred to the present Tay rail
bridge. At the time of the collapse Bouch was working on the design of
the proposed Forth Bridge. In consequence, the design of the bridge was
transferred to Benjamin Baker and Sir John Fowler.
Court of Inquiry was set up to try and ascertain the reason for
the collapse of the bridge. The Court of Inquiry report concluded that,
"The fall of the bridge was occasioned by the insufficiency of the
cross bracing and its fastenings to sustain the force of the gale." The
Court of Inquiry indicated that if the piers, and in particular the
wind bracing, had been properly constructed and maintained, the bridge
could have withstood the storm that night, albeit with a low factor of
safety - 4 to 5 was the norm at the time. Sir Thomas Bouch was held
chiefly to blame for the collapse in not making adequate allowance for
wind loading. He used a wind pressure of 10 lbsf/sq ft for the design
of the Tay bridge. It is interesting to note that when working on the
design of a proposed Forth bridge (1866) he used 30lbsf/sq ft. To this
day, however, there is still speculation as to the fundamental cause
and as to whether or not the designer, Thomas Bouch, was to blame.
Apart from the results of the original Court of Inquiry, various
theories have been put forward for the collapse including derailment of
the train. The picture shows the present Tay Rail bridge alongside the
pier remains of Bouch's bridge. It is a very emotive site and provides
a grim reminder of the disaster. The wrought iron girders which
remained standing after the disaster were transferred onto the present
bridge where they are still in use today. As the present bridge is now
over one hundred years old, inspection of the bridge is carried out on
a regular basis by Hi-Rope to check its structural integrity. In
addition, they have carried out detailed structural inspection of the
Findhorn bridge, Tyne bridge, Erskine bridge and the Forth Rail bridge.
Hi-Rope, one of the core compaies within the MB Engineering Solutions
group, have the tension netting system allowing exceptional access for
structural inspection where imposed and wind loading of traditional
scaffolding are prohibitive.
In order to test the conclusion of the Court of Inquiry and cast fresh
light on the event, a computer model of a pier of he bridge was
analysed under loading conditions based on modern wind analysis
techniques( Martin and MacLeod ).The findings of the study suggest that
the bridge was significantly underdesigned for the wind loading and
,even if the wind bracing had been properly constructed, had little
chance of surviving force 10 gales experienced in the Firth of Tay
area. The effect of the train on the bridge is also analysed to
determine whether it was necessary for the failure. In addition, the
collapse mechanism of the pier structure was examined with a view to
shedding new light on the disaster. The analysis suggested that the
uplift of the windward column was a significant feature of the collapse
mechanism. The question of how much blame can be apportioned to Bouch
in the light of the study is also addressed.