1. Tay Bridge Disaster

2. Background Railway Bridge spanning the Firth of Tay
Three and a half kilometres long
Designed by Thomas Bouch
Opened June 1st 1878

3. 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

5. 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?
Number of different theories
Official Inquiry
Wind Theory
Train Derailment Theory
Fatigue Theory

6. 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;

7. Wind Theory 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

9. 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

10. 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

11. Conclusions Combination of factors contributed to collapse of Bridge
“Badly designed, badly built and badly maintained”
Factors contributing to collapse:
Design
Maintenance
Storm
Consequences
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

12. Refrences http://taybridgedisaster.co.uk/
Forensic engineering: a reappraisal of the Tay Bridge disaster(Peter R. Lewis and Ken Reynolds)
en.wikipedia.org/wiki/Tay_Rail_Bridge