Chapter 2 of 24
Diagram Of Different Types Of Long Bridges
I've illustrated this with two examples. The first is a diagram of buildings drawn to the same size. These are examples of the longest bridge of each type.
At the top of the diagram is the longest suspension bridge, with a span of about 5400 feet; below is the longest cantilever bridge with a span of about 1800 feet; below that, the longest arch also about 1800 feet; and so on, illustrating with other types of bridges.
The suspension bridge is of course the type used for all large spans, and it is characteristic of this kind of structure that its greatest efficiency is at long spans. And you don't find the type at all in bridges below about 55 feet.
So I think you can give the general rule that,depending on the size of structure, you will use a certain type and it has a range between the longest span and the shortest. And when you get into another range of span, you will go to another type of structure.