2. CONTENTS
1. Introduction Muhammad Safeer Amjad 16-ME-008
2. Structure Muahmmad Bilal 16-ME-020
3. Precautions Mamoon Naeen 16-ME-024
4. Failure Syed Muhammad Wajeeh Shah 16-ME-004
5. Learn After Failure Hafiz Waseeq Hassan Zubari 16-ME-016
3. INTRODUCTION
Location:
Tacoma Narrows Bridge was the World’s 3rd
largest Suspension Bridge of the time of its
construction on 1st July 1940.
Located in the State of Washington in the
Pacific NorthWest from
“Tacoma to Kitsap Peninsula”
4. History:
o Idea Since: 1889
o Engineer: Leon Moisseiff
o Construction Started: September 1938
o Opened to Traffic: 1st July 1940
o Nick Name: Galloping Gertie
o Collapsed: 7th November 1940
o Type: Suspension
o Budget $6.4 million
5.
6. DIMENTIONS
• Total Length: 1810.2 m
• Longest Span: 853.4 m
• Width: 12 m
• Tower Height: 126 m
• Steel Stiffening Girder Height:: 2.4 m
• 1st Short Span: 335.28 m
• Central Span: 853.44 m
• 2nd Short Span: 335.28 m
7. o A small movement in the deck of bridge was noted many times by the
workers. ( During the Construction When wind blew)
o The oscillation steadily increased while
the bridge floor was placed. (
(Accordance with the wind Conditions)
o Several Precautions were taken to
reduce oscillations, but they were
unsuccessful)
8. PRECAUTIONS
Tie-Down cables were attached
and anchored to create blocks.
During the first storm they were
snapped
After Three days they were
reinstalled
9. To avoid movement and
stiffen the bridge, hydraulic
jacks were installed
4 buffers were added to act
as shock absorbers
No effect were given
10. FAILURE
Collapsed on 7th November
1940 at around 11:10 am
Speed of the wind at mid span
was nearly 60 Kmph
The bridge was bouncing…
The tie-down stays were
loosen
11. At around 10:30am the
wind speed increased to 64
Kmph, bridge started
twisting. (almost at 45
Degrees)
At 11:10 am the Structure
collapsed.
12. REASONS FOR FAILURE
Aerodynamic Flutter (Major
Cause)
Resonance Effect
Vortex Shedding
Fatigue and Torsional
Moments
13. REASONS FOR FAILURE
Resonance
• Frequency of oscillating bridge = Frequency of the wind
• Oscillatory Motion is induced by the vortex formation
General properties of Bridge
• Ratio of the width to length of main span so smaller
• Vertical stiffness was so much less
14. Aerodynamic instability:
Magnitude of the oscillation depends on the structure shape, natural
frequency and damping.
Oscillation caused by the periodic shedding.
Characteristics:
It was long narrow, shallow therefore very flexible structure standing in a
wind ridden valley.
Its stiffening support was a solid girder, which combined with combined
with solid floor, produced vulnerable to aerodynamic effects.
15.
16. LEARNED AFTER FAILURE
The Science of Aerodynamic flutter was born after Tacoma Bridge
failure.
This large tragedy was big wake up call to safety measures.
Effect of resonance on bridge and other flexible structures were studied
thoroughly.
Vortex shedding and its affects on the bridge were also taken into
account.
Wide use of open stiffening trusses to let wind pass through started.
17. Increased the weight of Bridge:
Vertical oscillations resistance α Mass of Bridge
Increase the Stiffness:
Using stiff Trusses
Increase the depth of Deck