Transcript tacoma group 4.ppt

Countdown to Disaster
The collapse of the Tacoma
Narrows Bridge
By Group 4
Prologue

One of the most famous civil engineering
disasters ever
The bridge collapsed on November 7, 1940.
It only opened a few months before
collapsing
?
Why did it collapse?

Bad design
Extreme Proportions
 New analysis led to lighter deck
 Aerodynamics not understood

Failure Mechanism

Longitudinal Resonance

Torsional Resonance caused collapse
Energy

Stability in terms of energy:

Energy input from loading (eg wind) = Energy
dissipated by elastic deformation of the
structure or plastic + heat etc
But this was not the case with the Tacoma
Narrows Bridge
Tacoma Problem….

Energy from wind load < energy dissipated
by deformation
How does lateral load cause the
bridge deck to move up and down?

This doesn't make sense? I thought wind
was a horizontal load

Nope, ‘Vortex Shedding’ gives lift
Anti-Dampening
Elastic Recovery
Stall
Lessons to be learned

Understanding of aerodynamics required
to create unique designs


Modelling, Wind tunnel etc
Accounting for local conditions