1. Tacoma Narrows Bridge “The Galloping Gertie”

2. Why was it built? Commissioned in 1937 to cross the Tacoma Straits of Puget Sound Commissioned in 1937 to cross the Tacoma Straits of Puget Sound Connected Tacoma and Gig Harbor Connected Tacoma and Gig Harbor

3. People Leon Moisseiff ( 1872- 1943) Leon Moisseiff ( 1872- 1943) –Bridge Designer –Worked on Manhattan and Whitestone Bridges –“Deflection Theory” Stated that the following three opposing forces act on the deck and suspension cables: Stated that the following three opposing forces act on the deck and suspension cables: –one downward force caused by the load of the roadway –one force in one part of the cable, pulling up and to the left –one force in the other part of the cable, pulling up and to the right

4. Frederick B. Farquharson Civil Engineering Professor at Univ. of Washington Civil Engineering Professor at Univ. of Washington Commissioned to analyze Moisseiff’s Design Commissioned to analyze Moisseiff’s Design

5. Dynamic Model of the Tacoma Narrows Bridge

6. Another Suspension Bridge… Total Length: 5,000 ft Total Length: 5,000 ft Center Span: 2,800 ft Center Span: 2,800 ft Tower Height: 420 ft Tower Height: 420 ft Force Loads Force Loads

7. Comparisons Bridge Center Span (ft) Width (ft) Ratio Geo. Washington 35001061:33 Golden Gate 4200901:46 Tacoma Narrows 2800391:72 Width to Span Ratio

8. Girder Depth to Span Ratio The Norm 1:90 Golden Gate 1:168 Tacoma Narrows 1:350

9. 3 Suspension Bridges George Washington Bridge Golden Gate Bridge Tacoma Narrows Bridge

10. Tourist Attraction

11. Trussed Girder Cross Section Side View

12. Solid Plate Girder (Tacoma Narrows) Cross Section Side View

13. Oscillation

15. Aerodynamic Girder Cross Section

16. Why Did It Fall? Flexibility Flexibility –Very thin plate girder –Width to span Ratio Aerodynamics Aerodynamics –Plate girder vs wind Perpendicular Wind/Vortices Perpendicular Wind/Vortices

17. The one that fell and its replacement

18. 3 S’ Social Social –New design used less materials -> lower cost –Connected two sides of Puget sound Scientific Scientific –Suspension Bridge Force loads –Thin & Flexible –Solid Plate Girder Symbolic Symbolic –It fell down –Revolution in bridge engineering –Battle between architecture and engineering

19. DISASTER STRIKES