Transcript Tacoma Presentation[1].ppt

Tacoma Narrows
Bridge Failure
Group 4
Orla Clancy
Owen Naughton
Paddy Crean
Teresa O Regan
Introduction
A
brief history
 Reasons for failure
 How this could have been prevented
 What was learned
A Brief History
Situated in
Washington
separates mainland
from Olympic
peninsula
 River Puget Sound
narrows to approx.
1 mile
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A Brief History
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Third longest suspension
span
Revolutionary in design
and historic in collapse
Galloping Gertie –
notable oscillations from
onset
Four months after its
erection, collapsed in a
windstorm on November
7,1940
Original design altered
Reasons for Failure
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Three hypotheses for
failure
Oscillations caused by
strong winds
Failed during Torsional
phase of oscillation
Aerodynamic
instability with
negative damping
caused failure
Aerodynamic Instability
Lift applies a moment
to the bridge
Rotation causes
strain energy to
build
Stalls, reverses and
overshoots
How this could have been
Prevented
 Use
of open stiffening trusses
 Width to span ratio
 Dampen the bridge
 Use of members with higher I values
 Deeper trusses or girders
 Streamlining
 Untuned dynamic damper
What was Learned
 Understanding
how aerodynamic
forces interact with structures
 Wind-tunnel tests used
 New data on vortex shedding
 Highlighted limitations of deflection
method