Transcript The Tay Rail Bridge Collapse.ppt

The Tay Rail Bridge
Collapse
S.S. 4A6 Presentation
Introduction
• Brief History
• Collapse Theories
• Possible solutions
• Conclusions
• Questions
Brief History
• 2 mile length
• 85 separate spans (largest in World)
• Completed in Feb 1878
• lattice girders supported on slender cast
iron columns braced with wrought iron
struts and ties
Fig 1 – Tay Rail Bridge
Collapse Theories
• Court of Inquiry
• Strong Gale
• Blamed the designer for insufficient wind
bracing
• No of Theories evolved since
Collapse Theory No 1- Train Theory
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Kink in rail track
Uplift of train occurred
Shock occurs when carriages hit track
Cast iron lugs connecting the wind bracing
members to the columns, fractured
Collapse of the pier structure ensues
Computer structural Analysis-presence of the
train on the bridge not required for collapse.
Fig 2 Collapsed Bridge
Collapse Theory No 2 – Dynamic
Theory
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Dr Lewis – dynamic effects significant
Fatigue failure of the cast iron lugs
evidence - eye witness reportspiers oscillated from side to side whenever a
train crossed the bridge
Close inspection- fatigue and not overstressing
caused failure
dynamic theory not supported by any dynamic
analysis ?.....
Possible Solutions
• Cast iron, notoriously brittle & weak – steel
• Iron was cracking in very cold weather.- poor
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quality due to financial constraints on foundary.
Lugs holding the bracing were snapping off from
being “too tight”.- consideration to end
connections
Record of girders being used despite being
twisted – Unserviceable materials ?
Insufficient wind bracing
Conclusions
• Dynamic effects , fatigue & bad workmanship
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contributing factors but secondary issues only
Stongest evidence - bridge underdesigned for wind. It
blew over due to inadequate bracing.
Royal Commission on "Wind Pressure on Railway
Structures".
The commission carried out tests to determine
pressures due to winds at varying speeds on bridges
Established guidelines so as to prevent the reoccurrence
of the event.
Questions