The colours show the 3 main chapters of a Suspension Bridge.Light blue for the suspension system.
Red for the main deck
Green for the foundations
The light blue suspension system in turn has 3 main paragraphs.
The main cable which hangs between the towers like a washing line.
The set of hangers which are connected to the main cable and from which the main deck is hanging.
The two main towers which are like the props that hold up a washing line.
Each of these paragraphs are made up of sentences which are components or elements such as
the cables (usually multiple strands bound together in various ways) of the suspension system,
beams (usually made of smaller joined components) making up the main deck, and
slabs (often of concrete) making up the foundations.
Of course in a real bridge there are many more - you can enjoy yourself spotting them in the many examples under the Header Notable Bridges on the main pages or click here.
At the next level the words are the materials from which the bridge is made
- steel, concrete and timber as well as the natural materials of rock and soil in the foundations which must carry the forces imposed on them.
The letters are the constituents of the materials such as cement, sand, aggregate and water in concrete and iron, carbon and other minerals to make steel.
Clearly the number of levels (chapters, paragraphs, sentences, words and letters) are not just limited to those 5 in any real bridge
- they are much more complex but with a bit of practice you can sort them out.
Of course, looking outwards or upwards, there are levels above the whole bridge, since a bridge, like a book, is also itself a part.
It is part of a wider set of social systems including transport, business and cultural infrastructures.
Likewise, looking inwards or downwards, we could 'dig' deep into the material constituents since they are made up of connected molecules
which are made of atoms which are made of protons, neutrons and electrons and so on.
These green, blue and red chapters have their equivalents in other bridges too.
The diagrams below show simple versions for an open spandrel arch and for a Warren truss bridge.
In these examples the green foundations and the red deck chapters are similar
but the suspension chapter becomes the arch and spandrels in one and the triangular truss framing in the other.
Perhaps the simplest bridges to read, but not necessarily to understand technically, are beam bridges.
The three chapters are:-
the beams and girders which span the length of the bridge
the deck on which the traffic runs and the people walk - together with handrails, lighting and other services
So how do we choose which level to look at?
We choose a level which is appropriate for any problem we have to address.
So sometimes we see a bridge as a small part of an entire region.
Sometimes we look at the bridge deck (e.g. if the surface needs repair).
Sometimes we look at small components because they have worn out.
How we read a bridge depends on why we want to read it.