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John A. Roebling and the
Design of Suspension Bridges
1. Methods of stiffening suspension bridges
2. Evolution of form in Roebling's suspension bridges
3. Wind and dangerous oscillations in suspension bridges
4. Ambiguity of form vs. structural redundancy in suspension bridges
5. Artistic representations of the Brooklyn Bridge
Eiffel
Eiffel Brunel
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Load Paths in Suspension Bridges
Weight of Bridge Deck
T
C C
TT
Shape of cable?
Parabola
Load Paths in Suspension Bridges
Vehicle on Bridge Deck
T
C C
T
T
C C
Bending
Deck or Truss
Cable
Force
1. Cables have Stiffness2. Force Follows Stiffness
StiffnessResistance to Deformation
Load Paths in Suspension Bridges
Vehicle on Bridge Deck
T
C C
T
T
C C
Bending
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The Historical Record
Severely Damaged by Wind
Excessive Wind-Induced Motion
Longest Span
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Buffalo Creek Bridge (1917) 113 ft span
Union Bridge (1820) 449 ft spanSamuel Brown England
Brighton Chain Pier (1823) 225 ft spansSamuel Brown England
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Severely Damaged by Wind
Excessive Wind-Induced Motion
Longest Span
Menai Straits Bridge (1826) 580 ft spanThomas Telford Wales
C.L.M.H. Navier
Deformation !Weight
1Cable Stiffness:
Severely Damaged by Wind
Excessive Wind-Induced Motion
Longest Span
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Wheeling Bridge (1849) 1010 ft spanCharles Ellett West Virgina
Niagara Railroad Bridge (1849) 822 ft spanJohn A. Roebling Niagara River
Severely Damaged by Wind
Excessive Wind-Induced Motion
Longest Span
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John Augustus Roebling1806-1869
“The means employed are:
Weight, Girders, Trusses, and Stays.
With these any degree of stiffness can be insured, to resist
either the action of trains or the violence of storm . . .”
J.A. Roebling, Final Report, Niagara Bridge
Niagara Railroad Bridge (1849) 822 ft spanJohn A. Roebling Niagara River
Load Paths in Suspension Bridges
Vehicle on Bridge Deck
T
C
T
1. Suspension Cables2.3.
Load Paths in Suspension Bridges
Vehicle on Bridge Deck
C
Bending
1. Suspension Cables2. Bridge Deck3.
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Load Paths in Suspension Bridges
Vehicle on Bridge Deck
1. Suspension Cables2. Bridge Deck3. Diagonal Stays
T
C
T
“The means employed are:
Weight, Girders, Trusses, and Stays.
With these any degree of stiffness can be insured, to resist
either the action of trains or the violence of storm . . .”
J.A. Roebling, Final Report, Niagara Bridge
Niagara Railroad Bridge (1849) 822 ft spanJohn A. Roebling Niagara River
John Scott Russell (1839)
2nd Dryburgh Abbey Bridge (1818) 260 ft span Second Montrose Bridge (1840) 432 ft span
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Britannia Bridge (1850) 460 ft spanRobert Stephenson Wales
Niagara Britannia
Span Length 821 ft 460 ft
Total Length 821 ft 2 @ 1400 ft
Weight 2400 lb/ft 7000 lb/ft
Cost £ 100 /ft £ 215 /ft
Relative Stiffness 1.5 1
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John Augustus Roebling1806-1869
John Roebling’s
Suspension Bridges
1844 Allegheny aqueduct at Pittsburgh
1845 Smithfield Street Bridge
1849 Delaware and Hudson aqueducts
1855 Niagara suspension bridge
1856 Ohio river bridge at Cincinnati
1860 Sixth Street Bridge
1883 Brooklyn Bridge
Niagara suspension bridge - 1855
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Smithfield Street Bridge (1846) 188 ft spansJohn A. Roebling Pittsburgh
Sixth Street Bridge (1860) 344 ft spansJohn A. Roebling Pittsburgh
Allegheny River Aqueduct (18xx) 188 ft spansJohn A. Roebling Pittsburgh
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Delaware and Hudson Canal Aqueducts (1847-1850) 114 ft to 170 ft spans Pennsylvania & New York
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Ohio River Bridge (1856) 1057 ft spanJohn A. Roebling Cincinnati
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What is one method for imparting stiffness
to a suspension bridge?
What are the aesthetic implications of
this method?
Draw a quick sketch of such a proposal
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Flood tide below me! I see you face to face!
Clouds of the west – sun there half an hour high –
I see you also face to face
Crowds of men and women attired in the usual costumes,
how curious you are to me!
On the ferry-boats the hundreds and hundreds that cross, returning home,
are more curious to me than you suppose,
And you that shall cross from shore to shore years hence are more to me,
and more in my meditations, than you might suppose
-Crossing Brooklyn Ferry
Walt Whitman (1856)
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Washington Roebling
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Boss Tweed Tammany Hall
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Abraham Hewitt
Emily Roebling
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Brooklyn Bridge (1883) 1595.5 ft spanJohn and Washington Roebling New York
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20061888
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The Brooklyn Bridge was politically and
economically significant because it joined the
cities of New York and Brooklyn.
Can you think of other civil works that have
had similar political and economic meanings?
Are there places you would propose such a
construction?
Were the results positive, negative, mixed?
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Again the traffic lights that skim thy swift
Unfractioned idiom, immaculate sigh of stars,
Beading thy path--condense eternity:
And we have seen night lifted in thine arms.
“The Bridge”
Hart Crane (1930)
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Brooklyn Bridge
Innovative structural system of cables, stays and truss
Longest span in the world
Construction amidst political corruption
Transforms city of New York
Bridge itself is a unique experience
Inspires numerous works of art
The image of New York City
Scientific
Social
Symbolic
Suspension Bridge Statics
Load PathAll forces or loads must eventually get to the ground.
Can we trace the path of tension of compression?
TruckT
C
T TT
C
TruckT
C
T TT
C
How does Roebling’s introduction of diagonal stays introduce ambiguity to the load path?
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Free Body DiagramsA sketch of all or part of a structure, detached from its support
Tower base reaction
gravityCable
tension
Cable
tension
Tower base reaction
gravity
Cable
tension
Cable
tension
Main span length/2
cable sag
Notation
VB
w
H
H
L/2
d
A
Equilibrium
!MA = 0
VB
w
H
H
L/2
d
A
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Equilibrium
!MA = 0, Hd - wL2/8 = 0, H = wL2/8d
VB
w
H
H
L/2
d
A
Cable tension
w = loadL = sizeR = formH = function
H = wL2/8d
H = wLR/8
R=L/d
R,L transform w into H
VB
w
H
H
L/2
d
A
R = 10, H = 2 x 105
R = 6, H = 1.3 x 105
CompressionTension