This presentation explains the study of Tacoma narrows bridge collapse.

1. Group 1
Section D

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

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.

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