Tay Bridge Disaster.ppt

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Tay Bridge Disaster
Background
• Railway Bridge spanning the Firth of Tay
• Three and a half kilometres long
• Designed by Thomas Bouch
• Opened June 1st 1878
Construction and Design
• Six years to build
• 10 million bricks, 2 million rivets, 87,000 cubic feet of timber and
15,000 casks of cement
• Cost over £300,000
• Latice grid design using cast and wrought iron
• Consisted of 85 spans
• 72 were supported on spanning griders below the level of the
track,44m in length
• 13 were spanning girders above the level of the track “High
Girders”,74m in length
• 26.8m above high water level mark
Tay Bridge Disaster
• Approx 7:15 p.m on 28th December 1879 central span of bridge
collapsed
• Train crossing at time plunged into Firth of Tay killing 75 people
• Why did the bridge collapse?
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Number of different theories
Official Inquiry
Wind Theory
Train Derailment Theory
Fatigue Theory
Official Inquiry
• There is no evidence to show that there has been any movement or
settlement in the foundations of the piers;
• The wrought iron was of fair quality;
• The cast iron was also fairly good, though sluggish on melting;
• The iron columns, though sufficient to support the vertical weight of
the girders and trains, were owing to the weakness of the cross-bracing
and its fastenings, unfit to resist the lateral pressure of the wind;
• The supervision of the bridge after its completion was unsatisfactory;
• Trains were frequently run through the high girder at much higher
speeds than at the rate of 25 mph;
Wind Theory
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Wind estimated to be force 10/11
Westerly wind blowing at right angles to bridge
Gust of wind ,masonry which columns were anchored into, lifted up
Diagonal ties snapped, bridge starts to shake
Train enters onto high girders
Critical tie fails
Originally piers acted as set of 6 columns
Bridge very flexible and swaying violently
Train Derailment theory
• Kink in railway line
• Rear carriage derailed and hits bridge
• Shock shatters cast iron lugs connecting wind bracing members to
columns to fracture
Fatigue Theory
• Dynamic events caused by fatigue failure of lugs
• Earlier train – passed safely but caused structural damage, bridge in
critical state
• Sparks when trains passed
• Succession of pier failures
• Inspection of photographs suggests failure of cast iron lugs due fatigue
rather than overstressing
Conclusions
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Combination of factors contributed to collapse of Bridge
“Badly designed, badly built and badly maintained”
Factors contributing to collapse:
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Design
Maintenance
Storm
Consequences
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Extra buttresing added to existing bridges to strengthen against high
winds
Bridge across River Esk demolished and replaced
Bouch blamed for collapse and removed from design of Forth Bridge
Design using cast iron barred
Steel was approved for use in bridges
Refrences
• http://taybridgedisaster.co.uk/
• Forensic engineering: a reappraisal of the Tay Bridge
disaster(Peter R. Lewis and Ken Reynolds)
• www.dundeecity.gov.uk/centlib/taybridge/taybridge.htm
• www.open2.net/forensic_engineering/riddle/riddle_01.htm
• en.wikipedia.org/wiki/Tay_Rail_Bridge
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