Tacoma Narrows BridgeG 04

8/3/2019 Tacoma Narrows BridgeG 04

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GROUP No 04


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Introduction

Started : November 23, 1938

Opened : July1, 1940

Designed : by Leon Moisseiff

Designed as : suspension bridge

collapse of bridge : November 7, 1940


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Cont

Greatest Span : 2,800ft

Total Length : 5,979ft

Cost : $8 million

Diameter of Cables : 17.25

6,308 wires spun one at a time to make the large cables.

Third largest suspension span in the world at the time.


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Location Map


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Design Included

Suspension bridge

Two Towers

Two Main Cables

Two Anchorages

One Lane Highway


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Anchorages


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600 ton blocks ofconcrete were used to

anchor the caisson


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Collapse


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What happened ??? The torsion mode shape was such that the bridge

was effectively divided into two halves.

The two halves vibrated out-of-phase with oneanother.

A suspension bridge may either twist as a whole ordivide into half spans with opposite rotations.

Nature prefers the two half-span option since thisrequires less wind energy.

The bridge collapsed during the excitation of thistorsion mode.


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Tacoma Narrows Bridge Collapse
http://www.youtube.com/watch?v=HxTZ446tbzEhttp://www.youtube.com/watch?v=HxTZ446tbzE


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Random turbulence

Periodic vortex sheddingAerodynamic instability (negative damping)

Failure Theories


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Random turbulence

The 42 miles per hour windscaused the resonance

Examples for Resonance:Soldiers marching in lockstep

over a bridge can destroy itby creating resonance

A swing set

When the natural frequency of vibration matchesthe frequency of oscillation, resonance will

occurred.


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Periodic Vortex Shedding

Natural vortex shedding frequency was calculatedto be 1 Hz

Torsion mode frequency was 0.2 Hz


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Solid Plate Girder (Tacoma

Narrows)

Cross Section

Side View


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Aerodynamic instability

(negative damping)


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Aerodynamic Girder

Cross Section


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Causes for Failure

The Tacoma Narrows Bridge collapsed because the

designer failed to consider the aerodynamic forces.

Steel beams used as main horizontal supports inthe bridge. It caught the wind rather than letting it

pass through.

Aerodynamic failure has to do with the stiffness ofsteel and its tendency to bend and twist if the

wind comes in at certain angles.


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How to prevent it from

happening again ??? Considering the location and geography before

the designs of a bridge or structure.

Taking into account aerodynamic instability, andeven resonance, along with other forces of nature.

Improvements in other areas more reliablematerials, expanded technical knowledge, wind

testing, computer technology, and the growingrecognition that failures, having the most to teachabout successful design.


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Conclusion

Key data of Tacoma Narrows bridge Included elements of design

Collapse

Theories of failure

Causes for failure of bridge How to prevent it from happening again?

We should remember that aerodynamicinstability, and even resonance, shouldalways be taken into account, alongwith other forces of nature.


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References University of Washington Special Collections-

Tacoma Narrows Bridge. November 16, 2006.

WSDOT- Tacoma Narrows Bridge: ExtremeHistory. November 16, 2006.

www.wsdot.wa.gov/TNBhistory/

www.advance.uconn.edu/01100109.html

The Urban Legend Archive. Bridge Resonance

National Scientific Seminar on Dynamics andProgressive Collapse in Cable-Stayed Bridges

Hanoi University of Science and Technology,Hanoi, Vietnam, February 16, 2011


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"These long-forgotten difficulties with

early suspension bridges, clearly show

that while to modern engineers, thegyrations of the Tacoma bridge

constituted something entirely new and

strange, they were not new--they had

simply been forgotten.


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THANK YOU.

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Tacoma Narrows BridgeG 04