TACOMA
NARROWS
BRIDGE
DISASTER
HISTORY
First opened to traffic on 1st July 1940
 Cable-stayed bridge built instead of truss
bridge.
 Designed to support two lanes of traffic, it was
only 12m wide, and 2.45m high.
 Collapsed 4 months later on the 7th November
1940.

PROBLEMS


Shortly after its
inauguration, the bridge
began to oscillate in
winds.
Team assembled to solve
problem, but they could
not rectify it in time.
COLLAPSE
EXTENT OF COLLAPSE




At its maximum twist, one side of the bridge was
8.5m higher than the other.
One of the suspension cables snapped, causing a
600ft length of the centre span to break away and
fall 190ft into the water below.
The vibration of the bridge lasted 3 hours before the
bridge collapsed.
There were luckily no fatalities (except Tubby the
dog)
REASONS FOR COLLAPSE





Bridge had solid plate girders, instead of a trussed
structure, and therefore had greater wind loading.
Under medium to high winds the bridge twisted and
resonated.
Opposite sides of the bridge resonated at a different
phase, causing the torsional vibration.
Has since, been proven that cause of collapse was
aerostatic flutter.
The aerodynamic forces on the bridge coupled with
the bridges natural mode of vibration, produced
periodic motion.
NEW BRIDGE


New bridge built in
1950 with greater ratio
of depth of stiffening
truss to span length,
and open steel grid
slots to allow wind to
pass through it.
Second parallel bridge
built to accommodate
traffic was opened in
2007.
LESSONS LEARNT



Every suspension bridge is now tested extensively in
a wind tunnel as part of its design.
Boosted research in the area of aerodynamics and
aeroelastics.
Now used as a cautionary tale for engineering
students throughout the world.