The Collapse of the Tacoma Narrows Bridge

 


On the morning of November 7, 1940, motorists on the Tacoma Narrows bridge in Washington state noticed something strange, the asphalt road on the bridge swaying like waves. Soon, almost the entire bridge, starting from the support poles and the supporting wires, moved like waves. At around 11 a.m. the swaying bridge collapsed and plunged into the water.

Construction of the Tacoma Narrows bridge was completed just months before it collapsed, in July 1940. At the time the Tacoma Narrows was the third-longest suspension bridge ever built and surpassed only by the Golden Gate Bridge in California and the George Washington Bridge in New Jersey. Compared to the two bridges, the construction of the Tacoma Narrows bridge is very narrow and simple.

The proposed design is made with a very deep foundation underneath, a feature that provides great strength and stress, but that would also cost the company a lot. Finally, the design was put aside to save costs to make it cheaper. The bridge foundation was eventually made shallower to save millions of dollars. Although more frugal and inexpensive, these options quickly proved problematic. Even during construction, the bridge shows a lot of shaking during the wind.

While alarming, it was not considered dangerous enough to stop the construction of the bridge which was then inaugurated on July 1, 1940. Several containment measures have been attempted to reduce bridge sway. Hydraulic support was installed between the ramp and the tower, plus a long cable tether to the ballast on the side of the bridge. Both attempts proved to be fruitless, in fact, the hydraulic supports were damaged when the bridge was painted, rendering it ineffective, and the cables leading to the ballast were broken shortly after installation.

Washington Bridge officials are looking for other solutions to dampen the excessive movement. Their first attempt at the bridge was just five days before the bridge collapsed. On the day of the disaster, the traffic flow on the bridge was quite normal. When the bridge began to sway violently, it was closed to drivers. During the closure, it turned out that one of the cars was left in the bridge area. However, quickly those in the car managed to escape.

Unfortunately, their pet, a dog named Tubby, was left in the car. When the swaying of the bridge subsided for a few minutes, two men were running to try to save the dog, only Tubby bit one of them and refused to leave the car. Tubby was still on the bridge when it finally collapsed and fell into the river below. Tubby's body was never found.

An investigation was carried out to determine the cause of the bridge collapse. Many theories emerged and many contributing factors were finally discovered. First, the bridge structure turned out to be too flexible and fragile. The quality of the asphalt road and the bridge frame was also the reason the bridge collapsed. The supporting cable in the middle of the bridge also makes the road body twist when hit by strong winds.

On the day of the disaster, the bridge was hit by a very strong wind. When the wind hit the bridge, the bridge swayed violently with poor quality building materials weakening its construction. After the incident, several attempts were made to salvage the debris from the bridge structure.

The forceful shaking caused extensive damage and most of the metal components could not be salvaged. The intact concrete foundation was eventually reused in the construction of the new Tacoma Narrows bridge. Asphalt debris that falls into the water is left unattended, which eventually becomes an ecosystem of aquatic life and becomes an artificial reef. Other bridges in the area were strengthened to prevent a similar incident from happening again, the implementation of wind tunnel testing on bridges is also mandatory.



The collapse of the Tacoma Narrows bridge became a case study material demonstrating the importance of aerodynamics in bridge design for engineers around the world. Construction of the new Bridge, delayed by World War II finally opened in 1950 and operated without major incident for several decades. The bridge was so popular that a second bridge was built beside it to support the traffic capacity. The new bridge is designed similar to the adjoining bridge and opened in 2007.

Post a Comment

Previous Post Next Post