- Now that we looked at the history of Roebling,
and the education and his life experience,
let's move on to his three major works
beginning with the Niagara River Bridge,
821 foot span,
completed in 1855.
In 1850, we talked about the Britannia Bridge
in the UK by Stephenson.
This was a railway bridge
and it was intended to have suspenders,
hence, the awkward, tall towers.
The Niagara River Bridge at 821 feet needed those suspenders
and it also needed a deep deck just like Britannia had.
Here the span is much larger,
therefore, the truss and the cables both are needed
whereas, again, in the Britannia,
only the deep deck was needed.
The Niagara River Bridge essentially established
Roebling's reputation as a master builder
of suspension bridges.
Roebling had a rival,
just like Stephenson and Brunel were rivals,
but they were rivals, but friends,
Roebling was not friends with his rival
and that rival was Charles Ellet.
Charles Ellet actually was awarded this project
for the Niagara River Bridge but
before the project starts,
Ellet gets fired for reasons unrelated to the project.
While Roebling was building his Niagara River Bridge,
the Wheeling Bridge over the Ohio River,
another suspension bridge that was built by
Charles Ellet, collapses in a wind storm.
This gets Roebling nervous and he asks Trenton
to send over more wire rope.
So if you look at images of the Niagara River Bridge
we see that he's attached the cables
to the bottom of the deck down to the ground.
So not a very elegant solution, but a safe one.
And the Niagara River Bridge was safe against wind.
During the Civil War, there was a concern that this bridge
would be destroyed, therefore,
Union soldiers guarded this bridge.
It was considered an important bridge.
Now let's move onto the Cincinnati Bridge.
This was completed between the time period
of 1856 and 1866.
It was interrupted by the Civil War.
This spans over the Ohio River
and slightly over 1,000 feet in span.
So we went from about 500 feet order of magnitude
in the last lecture over in the UK
with Telford, Stephenson, and Brunel
and now we're up to in the order of magnitude of 1000 feet.
And at the time that it was completed,
it was the longest spanning bridge in the world.
We can see with the Cincinnati Bridge
the style that Roebling is developing.
It's really the precursor, it's the prototype
to the Brooklyn Bridge.
Initially in 1846, Roebling had proposed two spans
on the order of about 788 feet each.
He revised that span to be one span
after the successful completion of the Niagara River Bridge.
So again, when completed,
it was the longest spanning bridge in the world.
Since it's completion, the Cincinnati Bridge
has been renamed after the engineer.
It is now called the John A. Roebling Bridge.
So with this background of Roebling,
his life, his experiences,
we can examine now his greatest masterpiece,
the Brooklyn Bridge.
So the rest of the lecture will be dedicated
to this masterpiece, the Brooklyn Bridge.
So how did John Roebling's vision
of the Brooklyn Bridge come about?
It actually happened in 1852,
that's when he got the idea for the Brooklyn Bridge.
He was on a ferry boat, stranded on the East River,
which is right behind me
because chunks of clogged ice blocked the channel.
He began dreaming and thinking about
a bridge crossing this East River
but it was a very large span and it would of
had to be much longer than the Cincinnati Bridge.
He wrote letters to the New York Press and eventually,
in 1865, a bridge company was born.
Now we're gonna examine the Brooklyn Bridge
from the scientific, social, and symbolic aspects.
So from the scientific aspect,
we're gonna look at some terminology
related to loads and the parts of a suspension bridge
and look at the form that it has for gravity and wind.
From the social point of view,
there's a lot of politics to talk about
and economy, of course, is closely related to
both politics and the social context.
And finally from the symbolic point of view,
we know it to be on of the greatest icons in the world.
We're gonna look at its opening and how the artist's
respond to this bridge.
A rendering drawn by one of John Roebling's assistants,
Wilhelm Hildenbrand, shows what the vision
of John Roebling was for the Brooklyn Bridge.
So with this rendering, we can see that indeed,
his vision, his original idea is what was constructed,
or very similar to it.
In the preface to report by John Roebling
to the New York Bridge Company in 1867, he wrote,
"The contemplated work when constructed
"in accordance with my designs,
"will not only be the greatest bridge in existence,
"but it will be the great engineering work
"of this continent and of the age.
"It's most conspicuous features, the great towers,
"will serve as landmarks to the adjoining cities,
"and they will be entitled to be ranked
"as national monuments."
This isn't exactly modest,
but actually history has shown it to be true.
The towers of the Brooklyn Bridge actually,
when completed, look like skyscrapers
in the context of the Brooklyn and Manhattan skyline.
Now I'll come back and show you that later.
From the scientific aspect of the study,
today I'm going to focus on some terminology,
for example the loads.
In engineering, we call dead load
something that's a permanent load in the structure.
It's essentially the self weight of the structure.
So in the case of the Bridge, it's the load of the deck
for example, would be something to be considered
the dead load of that bridge.
Then we have live load.
Live load, in the case of a bridge,
is the traffic load, the weight of the vehicles,
the weight of the pedestrians.
It's a transient load, something that's moveable.
That's what we refer to as live load.
We also have wind forces on any structure
buildings as well as bridges.
So we'll talk about a little bit about those wind forces
and what part of the suspension bridge,
the Brooklyn Bridge in particular,
is dealing with those wind forces.
Let me explain to you a little bit about
the different parts of the bridge
and the terminology used to describe the different parts.
We have the deck, and the deck of the bridge
is supported by the suspenders.
The suspenders are the vertical elements
of a suspension bridge and these elements
essentially pick up the load of the deck truss
which carries the dead load and the live load.
And the suspenders, then in turn
transfer their loads to the cables.
The cables are the draped cable that goes from
the top of one tower to the top of the other
and then back anchored against the anchorages
of these suspension bridges.
The cables transfer the load to the anchors
but also to the towers.
And the towers bring the load down to the foundation.
In the case of the Brooklyn Bridge,
we have stays.
Stays are the diagonal elements.
They're like the suspenders.
The suspenders are vertical,
the stays are diagonal.
And they essentially control the deformations
that could be induced by the dynamic effects of wind.
So Roebling learned this lesson
through the Wheeling Bridge collapse
and he applied those cables tying down the
Niagara River Bridge from the bottom of the deck
down to the ground,
a solution that wasn't very elegant.
In the case of the Cincinnati Bridge
and also the Brooklyn Bridge,
he includes these stays, these diagonal elements, again,
to control the possible deformations due to wind
through the lessons that he was learning
of the bridges that were having trouble
due to wind induced vibrations.
Some other terminology that you've heard of before
but I'm going to apply it in the context
of structural engineering is compression and tension.
So compression is when an element is being squeezed together
and tension is when the element is being pulled apart.
So when we look at a structure,
we have to be able to identify which parts
are in tension and which parts are in compression.
Because that is the foundation of how one goes about
designing those elements.
So I have a question for you,
if you look at this Brooklyn Bridge, look at the tower,
the cables, the cables again, are the elements that go from
tower to tower, they drape from tower to tower,
and look at the suspenders, those vertical elements
carrying the load from the deck to the cable.
Which of those elements are in tension,
and which of those elements are in compression?
The answer to the question of which elements are in tension
and which elements are in compression is Option A.
It shows that the tower is in compression,
the cable is in tension and the suspenders are in tension.
So through your homework assignments that you will be doing,
you will be able to understand this more fully
and also be able to calculate the actual forces and stresses
that these elements are carrying.
To continue the story of the Brooklyn Bridge,
I need to introduce to you Washington Roebling.
Washington Roebling is one of John Roebling's sons
and he received his degree in civil engineering
from the Rensselaer Polytechnic Institute, known as RPI.
It's a great school for engineering
and one of the first engineering schools
in the United States.
He was a colonel in the Civil War
and he worked with his father on the Cincinnati Bridge.
Towards the end of that Cincinnati Bridge project,
Roebling, actually Washington Roebling I should say,
actually took over most of that project
because John Roebling was busy preparing
for the Brooklyn Bridge.
Eventually, Washington Roebling took over the construction
of the Brooklyn Bridge as well.
In 1869, while surveying the East River determining
where exactly to place this Brooklyn Bridge,
John Roebling was standing on the piles of a dock.
As the ferry docked and pushed back those piles,
his toes got crushed.
He refused medical attention,
he believed in the healing power of water
and tried his own methods,
but unfortunately they didn't work
and two weeks later, John Roebling died of lockjaw.
Fortunately his son, Washington Roebling,
was educated in civil engineering
and he takes over the project.
Washington Roebling was a great builder
and a great engineer and well prepared to handle
what we would call, say, the technical aspects
of bridge construction.
But he was not prepared for the social part,
meaning the politics and corruption that would follow.