1. Countdown to Disaster The collapse of the Tacoma Narrows Bridge By Group 4

2. Prologue One of the most famous civil engineering disasters ever One of the most famous civil engineering disasters ever

3. The bridge collapsed on November 7, 1940. It only opened a few months before collapsing

4. ?

5. Why did it collapse? Bad design Bad design Extreme Proportions Extreme Proportions New analysis led to lighter deck New analysis led to lighter deck Aerodynamics not understood Aerodynamics not understood

6. Failure Mechanism Longitudinal Resonance Longitudinal Resonance

7. Torsional Resonance caused collapse Torsional Resonance caused collapse

8. Energy Stability in terms of energy: Stability in terms of energy: Energy input from loading (eg wind) = Energy dissipated by elastic deformation of the structure or plastic + heat etc Energy input from loading (eg wind) = Energy dissipated by elastic deformation of the structure or plastic + heat etc

9. But this was not the case with the Tacoma Narrows Bridge

10. Tacoma Problem…. Energy from wind load < energy dissipated by deformation Energy from wind load < energy dissipated by deformation

11. 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 This doesn't make sense? I thought wind was a horizontal load Nope, ‘Vortex Shedding’ gives lift Nope, ‘Vortex Shedding’ gives lift

13. Anti-Dampening Stall Elastic Recovery

14. Lessons to be learned Understanding of aerodynamics required to create unique designs Understanding of aerodynamics required to create unique designs Modelling, Wind tunnel etc Modelling, Wind tunnel etc Accounting for local conditions Accounting for local conditions