The Tacoma Narrows Bridge Disaster

Puget Sound, near the city of Tacoma, Washington, USA

November 7, 1940

Background:

The original Tacoma Narrows Bridge was known as "Galloping Gertie" because of its rolling, undulating behavior. It had a length of 5,939 feet (1,980 metres approx) and was opened to traffic on July 1, 1940 linking Tacoma and Gig Harbor by road.

The bridge was an unusually light design, and, as engineers discovered, peculiarly sensitive to high winds. Rather than resist them, as most modern bridges do, the Tacoma Narrows tended to sway and vibrate.This progressively worsened due to harmonic phenomena.

Four months after the opening of this bridge, there was a 42-mile-per-hour (70+km/h) wind storm around the bridge area on November 7, 1940. The wind caused the bridge to sway violently from side to side, and it finally tore the bridge apart. This incident happened because of the structure of the bridge itself which caught the wind instead of let the wind pass through. The combined force of the winds and internal stress was too great for the bridge, and it self-destructed.

No one was killed, as the bridge had been closed because of previous swaying. This is one of the best-known and most closely studied engineering failures, thanks in large part to the film and photographs that were taken to record the collapse.

IMAGES OF THE BRIDGE DURING ITS COLLAPSE

This image shows the twisting motion of the center span leading up to and just prior to failure.

Terminal torsional damage:

The nature and severity of the torsional movement is revealed in this image below taken from the Tacoma end of the suspension span. When the twisting motion was at the maximum, elevation of the footpath at the right was 28 feet (9m) higher than the footpath at the left.

Mortal damage has been sustained by the bridge - the beginning of the end:

This image below actually caught the first failure shortly before 11:00 a.m. on November 7, 1940 as the first chunk of concrete dropped out of the roadway. Also note bulges in the stiffening girder near the far tower and also in the immediate foreground. A few minutes after the first piece of concrete fell, this 600 foot (200 metre approx) section broke out of the suspension span, turning upside down as it crashed in Puget Sound. The square object in mid-air (near the center of the photograph) is a 25 foot (8.5 metre) section of concrete pavement.

Structural damage to bridge deck:

This image below shows the buckling of the suspended floor system near the centre of the side spans on the bridge deck. The top right picture shows the suspender connections and the type of cables used for this connection.

Damage to spans on each side of the bridge towers:

This image below shows the sag in the east span after the failure. With the centre span gone there was nothing to counter balance the weight of the side spans. The sag was 45 feet (15 metres approx).

Even the massive towers did not escape:

The towers were made out of structural carbon steel. This image below shows the size of the towers and the type of construction used. There is a slight buckling of the tower as a result of the additional strain caused after the centre span collapsed.

The remains of the bridge:

This image below was taken shortly after the failure. Note the nature of the twists in the dangling remainder of the south stiffening girder and the tangled remains of the north stiffening girder.

Ten years later, following the end of the Second World War, a new bridge was built. It was 40 feet (13 metres) longer than the first one.

CLICK HERE TO SEE A CONTEMPORARY NEWSREEL OF THE TACOMA BRIDGE DISASTER

CLICK HERE TO VIEW A NARRATED MOVIE CLIP