Engineering Structures 101: Bridges Page 1
Engineering Structures 101
Bridges
Compiled by
Professor Martin Fahey
School of Civil and Resource Engineering
The University of Western Australia
Pons Augustus, Rimini, Italy, AD 14. Typical
Roman circular arch bridge
Arch Bridges:
Types of Arches
Pont Neuf (“New Bridge”), Paris, 1578 / 1604. Circular Arch Bridge.
Engineering Structures 101: Bridges Page 2
Pont d’Avignon, France, River Rhone, 1188 Frére Benoît (St Bénézet), leader of “Brothers of
the Bridge” [revival of the Roman Guild of Bridge Builders Fratres Pontifices (Ponti-fices =
bridge-builders) or Frères Pontifes]. Destroyed deliberately by one of the Avignon Popes for
defence reasons. Arches made up of three arcs of a circle
Ponte Vecchio (“Old Bridge”),
Florence, 1345. Taddeo Gaddi.
Only bridge over the River Arno not
destroyed by retreating German
Army in WW2. A segmental arch
bridge (arches are segments of
circles).
Pont de la Concorde, Paris, built by Perronet, 1791. Segmental arches
(rubble from La Bastille used to construct the piers)
Construction of Pont de la
Concorde, Paris
Engineering Structures 101: Bridges Page 3
Common Bridge Types
Note that in all cases, the

main elements can be solid
or trusses.
Beam bridge:
bridge deck in bending
deck could be
solid beam (eg concrete), or
box section (steel or concrete box section), or
truss
Simple beam bridge: stone slabs on stone supports (Dorset, England)
Britannia Bridge, Menai Straits, Wales, 1850.
First railway bridge designed as deep box girder (two side-by-side rectangular tubes each containing a
single rail line). The designer (Robert Stephenson) included towers for adding suspension chains if
necessary. Main spans 460 t. wrought iron, total span 461 m consisting of two continuous wrought
iron tubes side-by-side. Destroyed by fire in 1970 by two boys!
Engineering Structures 101: Bridges Page 4
14th Street Bridge over the Potomac River. Continuous riveted steel girders. Note the absence of
internal hinges, and the roller supports at the piers
Continuous steel plate girder bridge. This 3-span bridge has a composite section consisting of the steel
girder and the concrete roadway on top. (Near Lausanne, Switzerland)
Continuous steel box girder bridge over the Rhine, Bonn, Germany, 1967. Note varying
depth of the box sections
Steel box girder bridge in Koblenz, Germany, collapsed during construction due to buckling. Similar
collapses occurred at Millford Haven, Wales, 1970 (4 deaths), and the Westgate Freeway Bridge,
Melbourne, 1970 (35 deaths), both designed by Freeman Fox .
Engineering Structures 101: Bridges Page 5
Concrete box section beam bridges: one
of the Florida Keys bridges, USA
(above), and the Linn Cove Viaduct,
North Carolina, USA (right).
(The Windan Bridge over the Swan River

on the Graham Farmer Freeway is a
concrete box section bridge, but
constructed by incremental launching).
Mt Henry Bridge Widening
Simply-supported box-section
prestressed concrete bridge,
BART system, San Francisco.
Hinge
Bollman Truss
Fink Truss
Pratt or Howe Truss
Warren Truss
(without verticals)
One way of strengthening a simple beam is
to use a truss.
Railway engineers in the US adopted
wooden truss methods for bridge
construction for the development of the
railway system in the US. Pictures show
some of the (many) types of trusses that
were developed.
Engineering Structures 101: Bridges Page 6
Fink “through truss”. 1868, Ohio, US. Compression columns are
hollow wrought iron tubes
Bollman Truss Bridge, Laurel, Maryland, USA. The existing bridge was built in 1869
along the B&O Main Line , and moved to the current location in 1888.
Crumlin Viaduct, Ebbw Vale,
Wales. Designed by Brunel
(1806-59), this early railway
viaduct is interesting in that it is

constructed entirely from pin-
connected iron members. Deck
support is by Warren truss
elements, simply supported.
Lift bridge, Sacramento River Delta A Warren truss with verticals is used throughout.
Lift span is simply supported. The double spans on each side are determinate due to
internal pins. (Near Rio Vista, California)
Engineering Structures 101: Bridges Page 7
Simply-supported steel truss railway bridge, UK
Steel Pratt truss spanning between
columns
Merchant Exchange Building.
The outside trusses of this
building consist of X-braced 50-
ft square panels. The clear
span between supporting
columns is 100 ft, and the end of
the building (foreground) has a
50-ft overhang. (Chicago,
Illinois)
Trusses are common elements
in many types of buildings
Circular Arch Bridge: Pons Fabricus (Ponte Fabrico), Rome, Tiber. Built in 62
B.C. by L.Fabricius. Oldest surviving bridge in Rome. Still used by
pedestrians. Note the hole through the centre - relieved water pressure in flood
conditions
Engineering Structures 101: Bridges Page 8
Earliest existing cast iron bridge: Ironbridge, River Severn, England,
built by Abraham Darby, 1779.
Ironbridge, River Severn, England, built by Abraham Darby, 1779.

Members in compression; connections using dowels etc.
Buildwise Bridge, River Severn, Thomas Telford (1796): cast-iron
bridge half the weight of the Ironbridge
Craigellachie Bridge over the River Spey. An historic bridge, being the first such
wrought iron truss arch bridge to be built by Telford in 1815.
Engineering Structures 101: Bridges Page 9
St Louis Rail Bridge, St Louis USA, Mississippi River. James Eades, 1874. First true steel
bridge. Three spans, each 152 m. Foundations were a major technical challenge (see next
slide)
Caisson used to construct piers of
St Louis Bridge. Deepest point
had 23 m water depth and 30 m
below riverbed. (50 m, or 5
atmospheres, of water pressure).
Men worked in pressurised
chamber at pressures up to 240
kPa (2.4 atmospheres). Because
of this, there were 91 cases of the
bends, 2 crippled for life, 13
deaths. Would have been much
worse except they realised slow
decompression and short shifts
were necessary.
20 m
40 m
Gateway Arch, St Louis,
USA.
This free-standing arch is 630
ft. high and the world's tallest.
Built of triangular section of

double-walled stainless steel,
the space between the skins
being filled with concrete
after each section was placed.
Shape is almost perfect
“inverted catenary”
Base of the Gateway Arch. The size of cross-section of the arch rib can be
seen by comparison with the figures on the ground. The section of the arch
at the base is an equilateral triangle with 90 ft. sides. The arch is taken 45
ft. into bedrock. (St. Louis, Missouri)
Engineering Structures 101: Bridges Page 10
Construction of the Gateway Arch (St. Louis, Missouri). Arch is not
stable on its own until complete.
Interior of Carmel
Mission. Built in 1793 it
is an interesting design in
that the walls curve
inward towards the top,
and the roof consists of a
series of inverted
catenary arches built of
native sandstone quarried
from the nearby Santa
Lucia Mountains.
(Carmel, California)
Garabit Viaduct, River Truyère, St Flour, France. (Viaduc du Garabit).
Built by Gustav Eiffel, 1884. Last (and best) of his many wrought iron bridges. Two-hinged
arch design became standard for many to follow. Note shape of the arch.
Garabit Viaduct, River Truyère, St Flour, France. (Viaduc du Garabit).
Built by Gustav Eiffel, 1884. Last (and best) of his many wrought iron bridges. Two-hinged arch

design became standard for many to follow. This photograph taken September 2002.
Engineering Structures 101: Bridges Page 11
Garabit Viaduct, Gustav Eiffel, 1884. The hinge at one end of the
arch.
Garabit Viaduct, Gustav Eiffel, 1884.
The bridge has been repainted
recently to a colour that matches the
original colour selected by Eiffel.
(photograph taken 2002)
Garabit Viaduct.The arches are broad at the base (for
stability) and are narrow, but deep, at the top.
Garabit Viaduct, Gustav Eiffel, 1884.
Engineering Structures 101: Bridges Page 12
Construction of the Garabit Viaduct. Hinged arch segments were tied back to the
towers using cables until they joined together. Compare with Sydney Harbour Bridge
construction (see later)
Pia Maria Bridge, Porto, Portugal
Gustav Eiffel
Eiffel Tower, Champs du Mars,
Paris. 1889. Grew from
Eiffel’s bridge-building
expertise. Was world’s tallest
structure for 40 years. 300 m
tower built of puddled iron. The
“arch” shape at the bottom is
purely decorative.
Graceful ironwork arches in the Musée d’Orsey, Paris, which is now the most beautiful
museum in Paris (more manageable in short visit than the Louvre), having being converted
from a disused railway station.
Engineering Structures 101: Bridges Page 13

Different types of arch
bridge configurations.
Pont Alexandre III, Paris, 1896 / 1898
(Widely regarded as the most beautiful of all of the bridges of Paris. This photograph pre-dates the
painting of the bridge for the 1989 bi-centenary of the French Revolution - much gold leaf added
then)
Steel arch of Pont Alexandre is a 107 m span ellipse with a rise/span ratio
of 1/17. Note the central hinge.
Pont Alexandre III. Detail of bridge
structure. Note the the casting over
the gap in the parapet and deck
expansion joint at the top of the
slide, and the gilt ornamentation
covering the support pin at the end
of the arch rib.
Without appropriate deck
discontinuities, the bridge would
not behave as a simple 3-hinged
structure.
Engineering Structures 101: Bridges Page 14
Pont Alexandre III. Detail of bridge structure. Note the gilt
ornamentation covering the support pin at the centre of the arch.
Pont Alexandre III. Re-gilding carried out for the bi-centenary of the
French Revolution (1788 – 1988). Dome in the background is Les
Invalides, the site of the tomb of Napoleon I
Sydney Harbour Bridge, completed 1932.
Almost
longest arch bridge in the world. (Longest is Bayonne Bridge, New York, completed
a few months earlier, which is 1.5 m longer). Two-hinge arch. The span between abutments
is 503 m to allow unobstructed passage for ships in Sydney Harbour. It contains 50,300 tons

of steel (37,000 in the arch). It is the widest (49 m) bridge in the world.
Sydney Harbour Bridge, completed 1932.
Engineering Structures 101: Bridges Page 15
Sydney Harbour Bridge, completed 1932.
Stages of construction of the Sydney Harbour Bridge.
Plougastel Bridge, River Elorn (Brest), France, 1929. Built by great French engineer
Eugène Freyssinet, pioneer of reinforced concrete construction.
For construction of the arches of the Plougastel Bridge, Freyssinet built a single timber
form, mounted on floating concrete caissons, which was floated into position, and the
caissons sunk onto the bottom
Engineering Structures 101: Bridges Page 16
Plougastel Bridge: Picture shows one arch completed, and the timber form in place for
construction of the second arch.
Salginatobel (Salgina Gorge) Bridge (1930) in the Davos Alps, Switzerland. This 3-hinged concrete
arch bridge designed by Robert Maillart has a span of 90 meters and a rise of 13 meters. The arch rib
increases in depth from the supports to the quarter-span points where it becomes integral with the deck,
and tapers to the mid-span hinge. This bridge was designated as an International Historic Civil
Engineering Landmark in 1991.
Schwandbach Bridge, 1933, Switzerland. Concrete arch bridge designed by Robert Maillart. Note the
sloping walls supporting the deck off the arch
Two slender fixed arch concrete highway bridges, crossing the Moesa Torrent, on the San Bernardino
Pass road, Switzerland. Designed by Professor Christian Menn, they are fine examples of modern
concrete bridge design. Arch span: 112 meters, column spacing on both approaches: 17 meters. Scale
of the structure can be seen from the figure, bottom left.
Engineering Structures 101: Bridges Page 17
Bixby Creek Bridge, Carmel, California, 1932. This fixed reinforced concrete arch
bridge spans 218 m across a deep river valley.
Fursteuland Bridge, River Sitter, Switzerland. A fixed reinforced concrete arch bridge,
crossing the valley in a single 135 m span
Gladesville Bridge, Sydney, Australia, 1964. Concrete arch bridge

Krk Bridge, Croatia (1964). World’s longest span concrete arch bridge (390 m)
Engineering Structures 101: Bridges Page 18
Wenner Bridge, Austria
Timber arch bridge
Menai Straits Bridge. Linking Wales and Isle of Anglesea. Designed by Telford and
completed in 1826. First major suspension bridge. Span of 176 m was unheard of for
any bridge and the chains were made of a new material: wrought iron links, all
individually tested. Span and 33 m headroom were required for shipping. Following this
example, many chain bridges were built.
Engineering Structures 101: Bridges Page 19
Menai Straits Bridge, 1826
Menai Straits Bridge.
Linking Wales and Isle of
Anglesea. This bridge,
designed by Telford and
completed in 1826 could be
described as the first major
suspension bridge. The span
of 176 m was unheard of for
any bridge and the chains
were made of a new material:
wrought iron links, all
individually tested. Span and
33 m headroom were
required for shipping.
Following this example,
many chain bridges were
built.
Clifton Bridge, River Avon near Bristol, England. Designed by I.K. Brunel in 1830, but not
completed until 1864, five years after his death. Main span 214 m; road 73 m above the

river. Telford advised Brunel against this design on account of its windy location, and the
wind problems he (Telford) had with the Menai Straits Bridge.
The chain (really 3 chains each side) used for the Clifton Bridge came from an earlier bridge
Brunel had designed, the Hungerford Bridge in London (1845).
Engineering Structures 101: Bridges Page 20
Clifton Bridge, River
Avon near Bristol,
England. Designed by
I.K. Brunel in 1830, but
not completed until
1864, five years after
his death. Main span
214 m; road 73 m
above the river. Telford
advised Brunel against
this design on account
of its windy location,
and the wind problems
he (Telford) had with
the Menai Straits
Bridge.
Hammersmith Suspension Bridge, 1887, London, England. Main span of 122 m
Double chains used in the Hammersmith Suspension Bridge, 1887, London, England.
Brooklyn Bridge over the East River, New York. 487 m span. Designed by John Roebling,
completed by his son (Washington Roebling) in 1883: First bridge to use steel wire
suspension cables. Much of the difficulty of construction was associated with the caissons
required to form the tower foundations.
Engineering Structures 101: Bridges Page 21
Brooklyn Bridge, New York
George Washington Bridge, New York. 1931. Span (1067 m) was 518 m longer than

the record at the time
George Washington Bridge, New York. 1931. Towers originally meant to be clad, but people
grew to like the look of the lattice structure, and so it was left as is.
George Washington Bridge, 1067 m span
Engineering Structures 101: Bridges Page 22
Golden Gate Bridge, 1937. Main span of 1280 m was the longest single span at that time
and for 29 years afterwards. Principal designer Joseph Strauss had previously collaborated
with Ammann on the George Washington Bridge in New York City.
Towers are 305 m high, the tallest of
their time.
Golden Gate Bridge, 1937. View from the
top of one of the towers, showing the main
cables and suspender cables. Section of the
cable, showing it to be made up of a bundle
of small cables.
Golden Gate Bridge, 1937. Cable “saddle” on top of one of the towers
Forth Road Bridge, over Firth of Forth, Scotland. Opened on September
4,1964.
Following sequence of slides illustrates some stages of construction
Engineering Structures 101: Bridges Page 23
Forth Road Bridge. Top of south tower showing the first wires of the cable being laid over the saddle.
The wires are 5 mm diameter with an ultimate strength of 1500 MPa. Each ‘strand’ contains 314 wires
, and there are 37 stands in each cable: 11,618 wires and 600 mm diameter.
Forth Road Bridge. View from the top of the south main tower. The so-called 'cable-spinning' operation,
originally devised by Roebling, consists of unreeling a continuous length of wire back and forth across
the bridge until a 'strand' is built up. The wire is looped round the wheel of the traveling sheave (shown)
which is connected to an endless hauling rope.
Forth Road Bridge. Looking up the cable to the south tower saddle. Note the bundles or
'strands' of wires that will form the finished cable. The individual wires are colour-coded
to assist in the spinning operation.

Forth Road Bridge.
Cable saddle at the top of the side tower.
Note the size of the saddle which has to
take the resultant vertical component of
cable tension due to the angle change in
the cable at this location.
Engineering Structures 101: Bridges Page 24
Forth Road Bridge. After the cable has been laid, the stiffening truss is constructed symmetrically about
both main towers. This view, taken before the truss has reached the side towers or met at midspan,
shows the geometry of the finished cable supporting the unfinished truss.
Forth Road Bridge.
View of the south cable
anchorage at the same
construction stage as in previous
slide. Note the scale from the
figures to the left of the
anchorage.
Forth Road Bridge. Close-up of the unfinished end of the stiffening truss taken from the south side
tower. The truss has a warren configuration with verticals, and the top and bottom chords are box
sections. Note the scale of the truss from the figures on the closest vertical member. (See old Firth of
Forth Bridge in the background)
Anchor Block for the Rainbow Suspension Bridge, Tokyo Bay, Japan.
Engineering Structures 101: Bridges Page 25
Tacoma Narrows Bridge (Washington
State, USA)
Collapsed on November 7, 1940.
Caused by torsional oscillations induced
by vortex-shedding
/>Current suspension bridge decks have moved
towards aerodynamic shapes that do not suffer

vortex shedding (eg Humber Bridge, UK, 1981).
Severn Bridge 1966 (next slide) was first that
used this shape.
Replacement bridge
Tacoma Narrows
Main deck girder is now a
very deep open truss,
much stiffer in torsion
(and bending) that the
original, and less
susceptible to vortex-
induced vibrations.
Humber Bridge, UK, 1981
Severn Bridge, UK (1966). Revolutionary aerodynamic shape of the bridge deck avoided the
problems of wind-induced vortex shedding that caused the torsional vibrations of the Tacoma
Narrows bridge. Now the standard shape of suspension bridge decks.