The Forth Railway Bridge
When I was in college, I had a professor who said some memorable things which in turn ended up becoming favorite quotes of mine. For instance once he told us that if we took a certain approach to solve a problem we would be “up the estuary without adequate means of locomotion.”
There is another quote of his that I carried through the rest of my education and will continue to carry through my career and that is, “When in doubt, make it stout.” That is precisely what the designers of the Forth Railway Bridge did. Here is a picture of this monstrosity from back in the day:
Photo Courtesy of A.F. Kersting on http://www.britannica.com/EBchecked/topic-art/49468/5545/Forth-railway-bridge-Scotland
Yes, I said monstrosity. This bridge is one of the ugliest structures I have ever seen. Yet, it has a certain beauty to it… i guess. It kind of reminds me of a pug: so ugly that it’s cute. Whenever I see or think of the Forth Bridge, this is what immediately comes to mind:
Photo Courtesy of http://www.infoniac.com/science/voice-analysis-cannot-identify-someone-with-certainty-on-its-own.html
Do see what I mean? The whole bridge looks like voice sound waves. Or just sound waves with a lot of extra noise.
This 1.5 mile bridge is the world’s first major steel bridge, completed in 1890. It was built after the Tay Bridge collapsed in 1879 from experiencing high winds, resulting in the death of 75 passengers who were travelling across it by train. Here is a picture of the original Tay Rail Bridge:
Photo Courtesy of http://schools-wikipedia.org/images/523/52330.jpg.htm
There is an obvious difference between the two bridges: size. These two bridges are (were) physical proof of the saying, “When in doubt, make it stout.” Now, I don’t know if this was designed before or after the Tay Bridge fell, but either way, the engineers who designed this (Sir John Fowler and Benjamin Baker) actually were wise in their decision to create something so huge like the Forth Bridge. There would have been no way that the designs for a new bridge of any scale smaller than the one chosen would have been received very well at all.
Despite its size and lack of aesthetic appeal, there still are special things about this bridge. As I mentioned, it is the first major steel bridge built in the world. The reason why it was built in steel probably was the same it wasn’t built smaller. The Tay Bridge was built out of cast and wrought iron.
How the bridge works is very unique. It’s a balanced cantilever system with each “sound wave” acting as double cantilevers. The outside “sound waves” hold around 1000 tonnes (that is 10^6 kilos), which is about half the weight of the suspended spans plus their live load (i.e. trains and whatever they carry). Here is the famous age-old picture that explains simply what is going on:
This is Baker’s human cantilever model. The pull experienced by the larger men represents the tension experienced in the top part of the sound waves and the push in the struts they are sitting on represent the compression experienced in the bottom part of the wave. That’s a pretty clever design.
I have the feeling that this post pretty much bashes the Forth Bridge, so I’m going to end with something that will leave a better taste in your (and my) mouth. Even though there is just way too much going on throughout the bridge, at least lights can be attached to them and make it look cool at night. Enjoy:
Structures and Spans 
