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? 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 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 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

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