Tay Bridge disaster

Tay Bridge disaster
Details
Date	28 December 1879
Time	19:13
Location	Dundee
Country	Scotland
Rail line	Edinburgh to Aberdeen Line
Cause	Structural failure
Statistics
Trains	1
Passengers	70
Deaths	75 (estimate-60 known dead)
Injuries	0

The Tay Bridge disaster occurred on 28 December 1879, when the first Tay Rail Bridge, which crossed the Firth of Tay between Dundee and Wormit in Scotland, collapsed during a violent storm while a train was passing over it. The bridge was designed by the noted railway engineer Sir Thomas Bouch, using a lattice grid that combined wrought and cast iron. Major engineering flaws were the cause of the collapse, and the disaster ruined Bouch's reputation as an engineer.
Like all rail lines intended to carry passenger trains, the Tay Bridge had been subject to a Board of Trade inspection before it opened. The inspection was conducted over a three day period in February 1878 during what were described as 'favourable' weather conditions. The bridge was passed for opening subject to conditions such as a speed limit and minor remedial work. It is interesting however to note the following comment from the inspection report '... When again visiting the spot I should wish, if possible, to have an opportunity of observing the effects of high wind when a train of carriages is running over the bridge ...'.

During a violent storm on the evening of 28 December 1879, the centre section of the bridge, known as the "High Girders", collapsed, taking with it a train that was running on its single track. All 75 people believed to be on the train including 5 staff were killed, a figure which was only established by a meticulous examination of ticket sales, some from as far away as King's Cross. There were 60 known victims, but only 46 bodies were found, two of which were not recovered until February 1880.

Causes

Original Tay Bridge from the north

Tay Bridge after the disaster, from the south

Investigators quickly determined many faults in design, materials, and processes that had contributed to the failure. Bouch claimed to have received faulty information regarding wind loading, but his later statements indicated that he may have made no allowance for wind load at all. Bouch had been advised that calculating wind loads was unnecessary for girders shorter than 200 feet (61 m), and had not followed this up for his new design with longer girders^.
The section in the middle of the bridge, where the rail ran inside high girders (through trusses), rather than on top of lower ones (deck trusses), to allow a sea lane below high enough for the masts of ships, was potentially top heavy and very vulnerable to high winds. Neither Bouch nor the contractor appeared to have regularly visited the on-site foundry where iron from the previous half-built bridge was recycled. The cylindrical cast iron columns supporting the 13 longest spans of the bridge, each 245 ft (75 m) long, were of poor quality. Many had been cast horizontally, with the result that the walls were not of even thickness, and there was some evidence that imperfect castings were disguised from the (very inadequate) quality control inspections.
In particular, some of the lugs used as attachment points for the wrought iron bracing bars had been "burnt on" rather than cast with the columns. However, no evidence of the burnt-on lugs has survived, and the normal lugs were very weak. They were tested for the Inquiry by David Kirkaldy and proved to break at only about 20 long tons (20 t) rather than the expected load of 60 long tons (61 t). These lugs failed and destabilised the entire centre of the bridge during the storm.