>> During Telford's time, James Watt was a leading critic of bridges,
and he critiques Telford's design of a London bridge proposal.
And Telford takes this critique very seriously.
Telford is then asked to write an article on Bridges for The Edinburgh Encyclopedia
and when he writes this he critiques the Iron Bridge and others including his own,
and in this critique he uses the ideals of structural art,
although again, he's not using this terminology.
In this course we're going to critique bridges using the measures of structural art.
We're going to look at it from the scientific perspective,
looking at the materials, meaning efficiency.
From the social perspective, minimum cost, meaning economy,
and from the symbolic perspective where we have maximum personal expression
where we measure the elegance.
We call these critiques, when we compare one bridge
to another, a comparative critical analysis.
So, from the scientific point of view we're going to compare the form and materials.
Is it a suspension bridge?
Is it an arch?
Is it steel?
Is it concrete?
From the social point of view we're going to look at costs and utility.
What were the construction costs of these two comparisons?
And, we're going to look at not only the construction costs,
but the maintenance cost as well.
And, from the symbolic point of view we look at the appearance and the meaning.
We look at the form, the details, and the ideas.
So let's do a comparative critical analysis using the Iron Bridge that we already looked at
and The Craigellachie Bridge, one of Thomas Telford's later arch bridges made of iron.
From the efficiency point of view, the Iron Bridge is a semi-circular form.
The Craigellachie Bridge is "parabolic" and I put that in quotes
because it's not really truly parabolic, it's really a very flat circle.
It's a small slice of a circle.
The Iron Bridge is 100 foot in span and the Craigellachie is 150 foot in span,
and despite being 50 percent longer,
the Craigellachie has one third less material than the Iron Bridge.
So, from that point of view, the Craigellachie Bridge is more efficient.
From the economy point of view we don't have numbers, but we could look at it
and make guesses as to how it was constructed.
So, the Iron Bridge we see it's constructed of many different parts with many connections
versus the Craigellachie Bridge we see it is made in mass production.
The arch, you can see, it's separated in to seven segments.
There's little vertical elements that show you where those connections
of the segments are made, so it is mass produced,
and we can assume that it was more economical to build.
And, from the elegance point of view, we see the semi-circular for the Iron Bridge versus again,
"parabolic" for the Craigellachie.
Both are arch bridges, so both are carrying the loads in compression.
The shape of the Iron Bridge is what we define as mutilated, meaning if you look
at those arches, the lower arch goes completely through from one abutment
to the other uninterrupted, but the upper two arches are interrupted by the deck,
so those upper two arches are what we call mutilated
versus the Craigellachie Bridge has the arch that's unbroken.
It goes from one abutment to the other uninterrupted by the deck.
The spandrel is what connects the deck to the arch,
and in the Iron Bridge we see that they are circles.
They are there for essentially decoration, whereas for the Craigellachie we have triangles,
and those spandrel's are there for support.
Even though in this analysis we see that the Craigellachie Bridge essentially, say, wins
in the context of measuring for structural art, it doesn't destroy the idea
that the Iron Bridge is a great work,
because it was so innovative using this material iron for the first time.
It is a very important structural work.
Thomas Telford goes on to become the President of the first formal engineering society,
The Institution of Civil Engineers which is still in existence today in Great Britain.
He is the leading engineer of the modern world and he also considered himself an artist.
Telford is the first modern engineer to show that a concern
for aesthetic does not compromise the technical quality that can improve it,
and the people that we're going to talk about are the most accomplished and found engineers.
Technically competent, but also artists.
That is one of the themes that runs through this course.