tacoma narrows bridge

• Aeroelastic flutter


  Wind-induced oscillations in the bridge's structure caused it to vibrate and eventually collapse
• Tacoma Bridge collapse


  1. Wind speed increased

  2. Created a resonant frequency that matched the bridge's natural frequency

  3. Caused the bridge to vibrate

  4. Bridge eventually collapsed
• Tacoma Narrows Bridge


  • Designed with a low natural frequency
  • Made it more susceptible to vibration
• The physics of vibration contributed to the collapse of the Tacoma Narrows Bridge
• Engineer's fundamental job


  Compare loading conditions to strengths
• Loads faced by buildings and other structures

  • Floods
  • Snow
  • Rain
  • Ice
  • Earthquakes
  • Crowds of people
• Wind


  One of the most interesting forces faced by civil structures
• The Tacoma Narrows Bridge was a classic case study of engineering failure
• Suspension bridge


  • Deck
  • Two towers
  • Two main cables
  • Connector rods which suspend the deck
• Advantage of suspension bridges

  Can efficiently span long distances with only two towers, reducing the amount of material required and cost
• The Tacoma Narrows Bridge opened in July 1940 and was the third-longest suspension bridge in the world at the time
• The Tacoma Narrows Bridge used two narrow plate girders to stiffen the deck, giving it an iconic steel ribbon appearance
• The Tacoma Narrows Bridge was too flexible even under moderate winds, and was nicknamed "Galloping Gertie"
• The Tacoma Narrows Bridge collapsed dramatically only four months after it opened
• Resonance


  Where a periodic force syncs up with the natural frequency of a system, leading to large oscillations over time
• Vortex shedding


  An effect where a fluid flowing past a blunt object oscillates as vortices are formed on the backside
• Vortex shedding frequency near the natural frequency of the structure


  Can lead to major oscillations even with small amounts of wind
• The Tacoma Narrows Bridge experienced resonance from vortex shedding, leading to vertical undulations
• Aeroelastic flutter


  A phenomenon where any amount of twist in the bridge creates vortices that amplify the twisting motion
• Aeroelastic flutter eventually created too much stress in the suspension cables, causing the Tacoma Narrows Bridge to fail
• Modern bridges avoid flutter

  • Include a gap in the center of the deck so pressures can equalize
  • Make the bridge deck more aerodynamic to avoid creating vortices
• Wind-induced motion can also affect other civil structures like skyscrapers and power lines
• The main lesson from the Tacoma Narrows Bridge failure is a reminder of how profoundly capable we are of making mistakes when pushing the envelope