Tacoma look for when designing a major structure

Tacoma look for when designing a major structure

Tacoma Narrows BridgeA lot of things can go wrong when building or designing a major building, plane, bridge, or even a road. Engineers face the challenges to overcome these flaws or problems everyday when they are trying to design structures. The primary causes of engineering disasters are usually: Human factors, design flaws, material failures, extreme conditions or environments, and combinations of these reasons put together. There are many things an engineer has to look for when designing a major structure such as the Tacoma Narrows Bridge.

On July 1, 1940 the Tacoma Narrows Bridge was open to traffic and was the third longest suspension bridge in the united state during the 1940’s. It had a span of 5939 feet measuring the approaches. It had two towers of 425 feet tall that were connected to the bridge. During the design they picked that it should be a suspension bridge because it was only supporting cars which were much lighter then trains.

Due to only have cars on the bridge they used shallow plate girders instead of trusses because they didn’t cost as much and the bridge didn’t need to hold as weight up. The plate girders however did not allow the wind to pass through as the trusses did so it moved a lot and got the nickname of “Galloping Gertie.” The bridge collapsed on November 7, 1940 due to winds plus a broken cable in the middle of the bridge which made it unbalanced. The wind would come up and under the bridge and get it in a motion where it turned one way and then bounced back and the wind would hit it there.

It sent it into a twisting motion till it broke into pieces. The winds started at 35 mph that day and it was enough to get the bridge moving but then it went up to 42 mph which stayed constant for a while and broke the bridge. In 1950 they built the new Tacoma Narrows Bridge.

It used truss girders this time and they also put stiffeners into the bridge so it didn’t move. The truss girders also allowed the wind to pass through so it didn’t provide a moving force like the last bridge.All together this was a human error because they wanted it to be cheaper so they didn’t use trusses because it didn’t have to hold as much wait as most bridges have to. The end result is that they ended up using trusses so they could have used them the first time around and saved a lot of money when building the bridge. The engineers learned from their mistakes and now have a new Tacoma Narrows Bridge.Bibliography1. Irvine, Tom.

The Tacoma Narrows Bridge Failure. 29 Dec. 1999. 10Mar. 2005 .