Proceedings of Bridge Engineering 2 Conference 2009
April 2009, University of Bath, Bath, UK
CRITICAL ANALYSIS OF THE FIRST BOSPORUS BRIDGE,
ISTANBUL, TURKEY
Matthew Smith1
1
University of Bath
Abstract: This paper presents a critical analysis of the First Bosporus Bridge. The bridge crosses the Bosporus
Straits, uniting the two banks of Istanbul with a road crossing for the first time. The bridge was completed in
1973 and has a main span of 1074 m. This paper considers aspects of aesthetics, loading, strength, construction
and future requirements.
Keywords: Istanbul, Bosporus, Suspension Bridge, Aerodynamic Deck, Steel,
Fig 1.1 Elevation of the First Bosporus Bridge at night showing the coloured lighting [4]
1 Introduction
The First Bosporus Bridge is a steel suspension
bridge located in Istanbul, Turkey. The bridge is a well
used road bridge that has had a significant effect on
Istanbul [3].
Until the construction of the First Bosporus Bridge
there was no dry crossing between the European and
Asian sections of Istanbul. All transport between the main
city on the Europeans side and the suburbs on the Asian
side was done by boat, creating huge queues [3] at rush
hours effectively costing the country millions.
The First Bosporus Bridge was designed by Freeman
Fox & Partners, also responsible for the Severn Bridge
and the Humber Bridge and the similarity is visible in all
sections of design.
The design life of the bridge is likely to have been
100 years because the durability and cost of the materials
is relatively high as is the future requirement for a
crossing of the straits. The bridge has been in operation
for 36 years and has not encountered any serious
problems. The success of bridges designed in similar
ways by the same company inspires confidence that this
bridge will remain operational until the end of the design
life.
The bridge is more than just a way of getting from
one side of the straits to the other. It has become a tourist
attraction in its own right. During the night the bridge is
illuminated in coloured light [Fig. 1.1] (different colours
on different nights).
Freeman Fox & Partners were famous for their use of
an aerodynamic deck to produce long-spanning
suspension bridges. The Tacoma Narrows disaster of 1940
prompted the deck design to become very heavy to reduce
the effect of the wind however Freeman Fox & Partners
did not follow this trend in their bridges, giving the
elegant deck seen above and on the First Severn Crossing.
The bridge cost £15M in 1973; it was funded partly
by the Turkish government and partly by a European
Investment bank, backed by several European
governments and the EEC. To recoup the money spent on
the bridge a toll was (and still is) required to cross.
2 Aesthetics
2.1 Introduction
To better analyse the aesthetics of a bridge the 10
points set out in F. Leonhardt’s book ‘Bridges’ should be
considered [1][6]. These 10 points cover the main areas
which affect the aesthetics of a bridge and are used by the
majority of designers as a guideline to producing beautiful
bridges. These points are:
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Fulfilment of Function
Proportions
Order
Refinement of Design
Integration into the Environment
Surface Texture
Colour of Components
Character
Complexity in Variety
Incorporation of Nature
It is not necessary for a bridge to comply with all 10
points to be considered beautiful as many are subjective,
especially character.
2.2 Analysis
2.2.1 Fulfillment of Function
The function of the bridge can be clearly seen as a
highway suspension bridge supported by the cables which
hang between the towers. The function is made more
obvious by the thin aerodynamic deck that could not act
as a beam.
2.2.2Proportions
The bridge has a very large span and a thin deck
giving it a very slender look in elevation. The towers are
large and bold, therefore compliment the thin deck. The
proportions of the approach viaducts on either side of the
main suspension bridge are less desirable as the supports
look too slender, especially in contrast to the large tower.
In general the proportions of this bridge are very good as
with all of the Freeman Fox bridges.
2.2.3Order
The Order of the bridge is very good as the entire
deck is uniform and the spacing between the hangers is
also uniform. The approach viaducts have a thicker deck,
as this section is a multi span beam bridge; however this
change occurs in the tower and does not negatively affect
the aesthetics. The absence of cables from the approach
viaduct has a negative influence on the order.
2.2.4Refinement of design
The towers are tapered in the tradition of the Greeks
which improves the aesthetics of the bridge [9]. Although
done for structural efficiency the zigzag hangers and the
aerodynamic deck are refinements that are very pleasing
aesthetically. The choice to conceal all changes in deck
depth to the tower makes the change less obvious and
therefore a useful refinement.
2.2.5 Integration into the Environment
The local environment is urban on both sides of the
straits and therefore a modern bridge, constructed using
metal, fits well into the surroundings. The tall towers and
sweeping cables fit well rolling hills and large expanse of
water.
2.2.6 Surface Texture
The deck of this bridge is a smoother texture than the
tower which is widely recognized as a good aesthetic
choice [9]. The deck is not so smooth to be shiny but
combined with its slenderness works well with the
surroundings giving the hint of a reflection of the water
without looking too unnatural.
2.2.7 Colour of Components
The dark colour of the towers, cables and deck work
very well with the surrounding area and makes the
hangers seem almost invisible during the day. There is
nothing particularly impressive with the colouring until
the night when the bridge is illuminated in a variety of
different colours, Red and Purple work to the greatest
extent giving a modern, sleek and attractive look to a 35
year old bridge. One reason for the effectiveness of the
lighting is the integration into the structure, giving the
lighting a less forced feel [7]. Despite being an old bridge
it is well maintained and has not been too badly affected
through discolouring as some bridges are.
2.2.8 Character
There is nothing about this bridge that gives it great
character, in its structural system it is a simple suspension
bridge and blends well enough into the cityscape during
the day to mean it does not require character. During the
night however, the coloured lighting makes it into an
interesting and attractive bridge that does have character.
2.2.9 Complexity in Variety
Being a suspension bridge there is little that can be
added structurally and so anything extra would be solely
to add complexity and would ruin the functionality and
order of the bridge. This bridge works well in its
simplicity.
2.2.10 Incorporation of Nature
The First Bosporus Bridge does not relate to nature
any more than any other bridge and does not need to; it is
situated in the middle of a city and is above a busy trade
lane, it is likely that to try to incorporate nature into this
design would make it look out of place and absurd.
2.3 Summary of Aesthetics
In the key areas of aesthetics this bridge succeeds, it
is a simple and elegant bridge that exhibits the structure
clearly. The change in colour of the bridge between day
and night is almost like the bridge is changing its mood
and because of this, the character changes as well, from
the calm functionality of the day to the vibrant excitement
of the night. It is because of the bridges performance in
these points that it is a well placed and beautiful bridge.
To the lay person the curve of the cable improves the
aesthetics of the bridge [7] which may be another reason
for its success amongst the local people of Istanbul.
3 Dimensions
3 Loading
3.1 Introduction
3.1 Introduction
This information has been taken from The Bosporus
Bridge [3] or assumed.
Determining the loading on a bridge is a key part of
design and is well documented in BS 5400-2:2006 [2].
The major loading can be split into dead, super-imposed
dead, traffic, wind and temperature. This bridge was
designed with the intention of being a lightweight and
aerodynamic bridge to counter the large wind loads that
suspension bridges take. To carry out some rough
calculations into the efficiency of the bridge the loadings
on the main span will be estimated.
3.2 Deck
The cross section below [Fig 3.1] shows the
dimension of the deck.
3.2 Dead Loads
The dead loading includes all the structure of the
bridge and is always present during operation. The dead
loads are known values and should not be subject to
change and therefore a lower factor of safety is required.
The dead loading (unfactored) on the First Bosporus
Bridge can be estimated as follows:
Fig 3.1 A cross section of the deck, dimensions in mm [3]
Steel Deck
Steel Cable
Steel Hangers
299
69.9
1.0
kN/m
kN/m
kN/m
3.3 Towers
Both towers stand on two legs, each with their own
piers. The European side uses round piers with a diameter
of 18 m and begin at 17 m and 24 m below sea level. The
Turkish side however uses rectangular piers of 15 m x 19
m, beginning at just 5 m and 10 m respectively below sea
level. The reason for this difference is the difference in
soil materials on either side. The first 10 m of European
soil is too soft to support the huge structure of the bridge.
The towers are 165 m high have the rectangular plan
of 7 m by 5.3 m at the base. The towers are tapered from
5.3 m to 3.0 m at the top (viewed from the bridge). The
towers are connected by three horizontal members to
increase lateral stability. The cross section below [Fig.
3.2] shows the dimensions of the towers.
3.3 Super-Imposed Dead Loads
The super-imposed dead loads include all nonstructural permanent loading. These have higher factors of
safety due to the greater uncertainty in the materials and
the possibility of replacements being heavier than the
originals as the design life of these materials is lower than
the permanent structure. Below are estimations for the
main types of super-imposed dead loads (unfactored).
Mastic Surface
Handrails
Services and Finishings
22.6
2.0
2.0
kN/m
kN/m
kN/m
3.4 Traffic Loads
The main live loads that the bridge must withstand
are primarily vehicle loading as this is a road bridge.
There are many load combinations which need to be
analysed to get the most onerous cases of stress in the
bridge, both hogging and sagging must be investigated.
Vehicle loads can be split into HA and HB loading.
HA loading is a uniformly distributed load (UDL)
acting over a notional lane in conjunction with a knifeedge load (KEL). HA loading is the design loading for
heavy fast-moving traffic including bouncing factors [6].
Figure 10 and Table 13 of [2] are used to get the nominal
value for the UDL per lane of 18 kN/m. The KEL is taken
as 120 kN per notional lane (both unfactored) The HA
loading is taken over two lanes and then 1/3 of HA is
taken over all additional lanes to give the worst case
scenario. The First Bosporus Bridge has 4 notional lanes
on each side of the central reservation.
HB loading accounts for abnormal truck loading. The
unfactored load is taken as 10kN per axle per unit, with
the maximum number of units being 45 [2][6]. HB
Fig 3.2 Cross section of the tower, dimensions in mm [3]
loading is used together with HA loading to create several
load cases which should all be investigated.
There are also secondary traffic loads which should
be considered on any highway bridge, these include
longitudinal forces from acceleration or braking, taken as
8 kN/m along a single notional lane [2][6]. Collision
loading on the parapets equal to 25 units of HB loading
and accidental skidding which can be modelled as a point
load of 250 kN acting horizontally [6].
Fatigue loading is also linked with traffic loading and
requires consideration. BS 5400-10:1980 is a guideline to
fatigue checks [6].
3.5 Wind Loads
Suspension bridges are very badly affected by wind
loading because large spans and minimal lateral
resistance. It is not just the horizontal force which can
damage the bridge; wind could trigger the bridge to
vibrate at its natural frequency, leading to severe damage
and collapse as demonstrated in during the Tacoma
Narrows disaster of 1940.
To combat the effects of wind loading on the First
Bosporus Bridge, an aerodynamic deck was designed
which reduces the wind loading. In addition to the
aerodynamic deck the hangers are inclined in a zigzag
pattern which gives extra lateral stability. The estimated
wind loading acting on the bridge is taken from [2]
section 5.3.
The aerodynamic deck of this bridge sets it apart
from many other bridges of the time (especially in USA)
which, to combat the effects of natural frequency and
coupling use far heavier decks which generally detracts
from the structural efficiency, cost efficiency and
aesthetics
the design using approximate values estimated in section
3. These calculations are based on BS 5400-3:2000[5].
The load from the deck is carried through the hangers
into the cable which pass the load into the tower and the
anchorage. All loading on the approach viaduct is taken
by the columns.
To be sure that the bridge is able to withstand the
most onerous bending moments numerous load cases
need to be looked at. A fully loaded bridge does not
necessarily give the most onerous case.
All bridges designed to BS 5400 must be checked in
both ultimate limit state (ULS) and serviceability limit
state (SLS). The factors given in Table 1 of BS 54002:2006 [2] are different for ULS and SLS, with ULS
being greater.
4.2 Ultimate Limit State of Bridge Components
4.2.1 Hangers
The hangers are subjected to the dead, super-imposed
dead and live loading from the deck as well as their own
self weight. Each pair of hangers supports one 18 m
section of deck and 4 nominal lanes. The highest possible
live load is given by HA loading, full in two lanes and
one third in the other two lanes. The diameter of the
hangers has been assumed to be 150 mm, T460 grade
steel and γm = 1.15 this gives σdesign = 400 N/mm2
3.6 Temperature Loads
Temperature loading can be very detrimental to the
life of a bridge of this size. A change in temperature will
result in an expansion of the bridge and without
expansion joints a stress would be induced. The First
Bosporus Bridge uses ‘rolling leaf’ expansion joints
which need to be well maintained and kept free of
blockages to avoid the induction of stresses in the bridge.
The temperature on the bottom of the bridge is likely
to be far lower than the temperature on the top on a sunny
day, creating differential expansion which is far more
damaging.
3.7 Earthquake Loads
The First Bosporus Bridge is located in an earthquake
zone and therefore must be able to survive an earthquake.
The movement joints help to alleviate some of the forces
which the deck would experience in an earthquake.
4 Structure
4.1 Introduction
This section aims to replicate the calculations that
would have been completed in the design stage. They are
simplified calculations that focus on the major details of
Fig 4.1 Diagram showing factored loading and
maximum force in hangers
ߪ = ܲ/‫ܣ‬
σ = 3.74 x 106 / (π x 752)
σ = 211 N/mm2 < 400 N/mm2
(1)
This should give the required redundancy in case one
hanger requires replacement.
4.2.2 Cables
The huge cables must take all the loading from the
deck as well as the self weight from the hangers and itself.
The angle between the horizontal and the cable at the
tower is 17° and the diameter of the cable is 760 mm as
explained in section 5.4. The tensile strength of the cables
is 160 kg/mm2 [3].
ࡼ࢜ = ૙. ૟૚૜ × ૞૜. ૚૛ × ૚૙ૠ૝ × ૚ૡ × ૙. ૠૢ
= ૛૟. ૜ ࡹࡺ
Fig 4.2 Diagram showing the factored loading on the
entire cable
This is a beneficial load and therefore has a factor of
1.00 whereas the horizontal load requires a factor of 1.40
if considered with dead load only and 1.10 which used in
conjunction with other loading conditions.
The factored Pt load (as a secondary loading
condition).
૟. ૟ૡ × ૚. ૚૙ = ૠ. ૞૚ ࡹࡺ
4.4 Temperature
Fig 4.3 A free body diagram at the cable-tower
connection
ߪ = ܲ/‫ܣ‬
σ = 606 x 106 / (π x 3802)
σ = 1371 N/mm2 < 1569 N/mm2
4.3 Wind
The steel deck has a coefficient of thermal expansion
of 12 x 10-6 /K. Assuming an increase in temperature of
25 K.
(5)
∆ࡸ = ࡸ∆ࢀࢻ
∆ࡸ = ૚૙ૠ૝ × ૛૞ × ૚૛ × ૚૙ି૟ = ૙. ૜૛ ࢓
This change in length is acceptable and will be
negated by the expansion joints. The stress induced in the
deck should the expansion joint fail to work because of
blockage or poor maintenance is calculated in equation 6.
࣌ = ࣕࡱ =
[2][6]
࢜ࢉ = ࢜࢈ ࡷ૚ ࡿ૚ ࡿ૛
(2)
࣌=
∆ࡸ
ࡱ
ࡸ
(6)
૙. ૜૛
× ૛૙૙ × ૚૙૜ = ૟૙ ࡺ/࢓࢓૛
૚૙ૠ૝
vc is the basic wind speed which has been estimated
to be 25 m/s. This is a conservative estimate. K1 is the
wind coefficient, which equals 1.55. S1 is the funnelling
factor which, because of the low lying land surrounding
the bridge which makes funnelling very unlikely, is taken
as 1.00. S2 is the gust factor which at 64 m is 1.37 [2][6].
This stress must be factored using the loading factors
taken from Table 1 [2]. γF3 = 1.30
࢜ࢉ = ૛૞ × ૚. ૞૞ × ૚. ૙૙ × ૚. ૜ૠ = ૞૜. ૚ ࢓/࢙
This stress is acceptable and below the capacity of
the steel.
This value can be converted in to a horizontal force
based on the exposed area of the bridge. It does not
account for the aerodynamic reduction [6] which this deck
would give, therefore it is conservative.
Clause 5.3.3 [2][6]
ࡼ࢚ = ࢗ࡭૚ ࡯ࡰ
(3)
q is the dynamic pressure head is equal to 0.613vc2
[6]. A1 is the area of the bridge which faces the wind. CD
is the coefficient of drag which is taken from [2] as a
function of the b/d ratio. From figure 5 of [2] CD can be
taken as 1.2.
ࡼ࢚ = ૙. ૟૚૜ × ૞૜. ૚૛ × ૚૙ૠ૝ × ૜ × ૚. ૛ = ૟. ૟ૡ ࡹࡺ
The vertical force can also be calculated using similar
formula.
Clause 5.3.5[2]
ࡼ࢜ = ࢗ࡭૜ ࡯ࡸ
(4)
A3 is the area in plan and CL is the coefficient of lift
which can be found from figure 6 of [2]. Assuming α =
10° CL is equal to be 0.79
࣌ = ૟૙ × ૚. ૜૙ = ૠૡ ࡺ/࢓࢓૛
4.5 Natural Frequency
Using the Rayleigh-Ritz equation the natural
frequency of the bridge can be estimated. This value
should be above 5 Hz in the vertical direction while
unloaded [6].
ாூ
݂଴ = (ߚ௡ ݈)ଶ ට௠௟ర
(7)
(Βnl)2 is 22.37 for this case. E is the young’s
modulus of steel, 200000000 kN/m2. I is the second
moment of area which has been calculated as 24.4 m4.
m is the mass density per unit length of the section at
mid span. For the horizontal case dead and superimposed dead loads only are included giving 72600
kg/m. l is the length of the deck, which is 33.4 m
200000000 × 24.4
݂଴ = 22.37 ඨ
72600 × 33.4ସ
݂଴ = 22.37 × 0.23 = 5.19 ‫ݖܪ‬
This value is acceptable falling above the 5 Hz limit
stated above and below the 75 Hz that if exceeded is
uncomfortable.
4.6 Load Cases
The most onerous situation is not necessarily the
highest loading and designers must consider many
different load cases to be sure that the bridge is suitable.
Designers must consider temperature, traffic, wind and
dead loads all acting together however to counter the fact
that this unlikely BS 5400 lowers the factors of safety on
the secondary live loading. This section contains a few of
the load cases that will have been considered in design.
4.6.1 Load Case 1
The load case depicted in [Fig. 4.4] is designed to
give the maximum sagging moment.
Fig 4.5 A drawing showing simplistically the positioning
of the primary traffic loads and a moment diagram
4.7 Foundations
The European side substructure is founded on
contorted mudstone or schistose rocks of the Upper
Devonian age [3]. The rock strata have undergone a large
amount of folding and it is very difficult to predict the
type and strength as the orientation changes every few
metres. These folds have also lead to the rock becoming
fractured and soft, in particular underneath the anchorages
[3]. The unpredictability and the softness of the rock
mean that the excavations on the Europeans side are far
greater than those on the Asian side where the bedrock is
limestone [3].
5 Construction
5.1 Introduction
Fig 4.4 A drawing showing simplistically the positioning
of the primary traffic loads and a moment diagram
4.6.2Load Case 2
This load case is an attempt to find the greatest
hogging moment in the deck. The factor of the live traffic
loads have been reduced to 1.30 for both HA and HB in
accordance with [2].
Bridge construction is unlike almost all other types of
construction because there is no firm place to rest
machinery and plant cranes. In the case of the First
Bosporus Bridge barges were used to put the deck into
position. The towers were constructed first, followed by
the cables and then the deck, connected to the hangers in
stages, starting in the centre and working out towards the
towers. Much of the information for this section was
gathered from [3] The Bosporus Bridge, Sheridan Group.
5.2 Foundations and Anchorages
The cables carry large horizontal loads and this must
be transferred into the ground at a point behind the tower.
The anchorages on each end take a 15400 tonnes per
cable [3] which is a huge force and requires significant
foundations. It is important that these are situated in a
position where the ground has good geotechnical
properties. When the cables reach the anchorages they
splay into their separate strands, each of which is
connected into a shoe which is bolted with steel slabs into
the prestressed concrete anchor slabs. The trenches (up to
28 m deep) are stepped [Fig. 5.3] and crosswalls are
constructed [Fig. 5.4] to increase the sliding resistance.
The Ortakoy (European) anchorage contains 60000
tonnes of concrete as a counter load to the cable force.
The Beylerbeyi (Asian) side anchorage contains 50000
tonnes [3] of concrete which gives a factor of safety for
the anchorages of over 3 in both cases.
Fig. 5.1 The anchorage block during construction [3]
Fig. 5.6 The connection between the anchorage and the
cable showing the reinforcement [3]
The piers for the towers were excavated into the
bedrock to get a firm footing. The soil conditions on the
European side of the bridge are far worse than the Asian
side. The European side required steel cofferdams to be
constructed to exclude the water while removing the soft
soil. All piers are close to the edge of the water to reduce
the span as much as possible.
Fig. 5.2 The anchorage during construction showing the
cables [3]
Fig. 5.7 One pier on the European side ready for insertion
of the pre-fabricated tower [3]
5.3 Towers
Fig. 5.3 (Right) One side of an anchorage after
excavation, showing the trenched system [3]
Fig. 5.4 (left) The same side of an anchorage during
construction, the crosswalls are almost complete [3]
The hollow rectangular cross sections of the legs
were constructed in Italy and were preassembled on
arrival in Turkey. This was considered the best method of
construction because of the added control the contractors
had over the situation, the tolerances of the straightness of
the tower were very low and no allowance for inaccuracy
in erection was made. The small margin for error which
the designers required meant that the greatest care had to
be taken when assembling and erecting the lowest section
of the towers [3].
Climbing cranes were required to lift each section’s
four panels into position [Fig. 5.8]. The crane started at
the bottom and worked up, connecting each panel to the
one below. Grip bolts and tension bolts have been used to
hold these in place.
5.4 Cables
The main cables have been formed through spinning
parallel-wires which is common to most suspension
bridges. This method was chosen over pre-formed
parallel-wire strands. The cables are made up of 19
strands of 550 wires, each with a diameter of 5mm. The
resulting main cable has a finished diameter of 760mm
after the spinning process.
Fig 5.8 A tower under construction showing the climbing
cranes at the top [3]
Fig 5.10 The beginning of the spinning process showing
one strand of 550 wires [3]
Fig 5.11 The process continues, joining strands [3]
Fig 5.9 The inside of one leg of the tower showing the
extensive steelwork [3]
Fig 5.12 A hydraulic compacter is used to give the cable a
circular shape [3]
Fig 5.13 The completed and loaded cable gets coated in
red lead paste for protection [3]
To put the wires into position two catwalks had to be
erected from the anchorages, through the towers,
following the proposed route of the cables, when the
cables were being lifted into position the Bosporus
shipping lane to be closed.
The hangers are then fixed to the cables using two
semi-cylindrical steel casings. These are then clamped
into place. To protect the wires from corrosion the cables
are coated in red lead paste and wrapped in a protective
casing of galvanised annealed steel wire once the full
dead load was attached.
Fig 5.15 The centre section is lifted into place [3]
5.5 Deck
The deck was attached to the hangers in sections,
starting in the centre. These sections consist of 18 m
length of the deck prefabricated 2 miles north of the
bridge in Göksu. Stiffened steel panels, typically 18 m by
2.5 m are used, imported from England or Italy and
assembled using automatic welding machines.
As with the towers the allowable inaccuracies were
small and therefore it was important that the deck boxes
fitted together perfectly. To achieve this each box was
assembled next to the box that it would be next to during
operation.
Barges were used to transport the completed box
units. As mentioned previously the centre section was the
first to be attached and then the boxes to either side of that
were attached simultaneously. Once a box had been
attached to the hangers it was temporarily bolted to the
adjacent box. This was designed to incorporate a lagging
procedure which harnessed the changing profile of the
bridge (especially the joint) while other boxes were being
connected. The final connection was made using welds.
Fig 5.14 The
sections of deck
are independently
lifted off barges
to be put into
position [3]
Fig 5.16 The box units under construction [3]
The 40mm thick mastic surface which the vehicles
would travel over was put down along the carriageway
once the welding was complete. The super-imposed dead
loads such as barriers and lampposts were attached
afterwards.
At the join between the deck, approach viaduct and
tower there is an expansion joint on both sides of the main
span. A ‘rolling leaf’ style joint was used [3]. The
expansion joint is not just to alleviate temperature induced
stresses in the structure but also acts to absorb earthquake
movement.
Fig 5.17 A ‘rolling leaf’ expansion joint [3]
5.6 Approach Viaducts
The approach viaducts are supported by columns. A
cantilever construction system is used starting at the
anchorages in the direction of the tower. The steeply
sloping sides of the bank mean that floating cranes are
required to bring the boxes into the foot of the tower.
Gantries running up and down the backstays are used to
lift them into their position [3].
growing. The format of the city, with the suburbs on one
side of the straits and the main city on the other, means
that the demand to cross is increasing. Due to the
increased traffic loading and the age of the bridge it is
unlikely that it would be feasible to expand the existing
bridge short of making the two emergency lanes
permanently for ordinary traffic. Should the demand
increase enough to make crossing the straits very time
consuming it is likely that the Turkish government would
opt to construct another bridge.
7 Conclusion
Fig 5.18 The Approach Viaduct under construction [3]
The First Bosporus Bridge was one of a series of
suspension bridges which has created a new, popular and
effective style of suspension bridge design. The bridge,
after completion, significantly improved the transport
situation in Istanbul [3] by removing the large queues for
ferries that had tainted so many commuters journey.
The bridge is aesthetically pleasing; complying with
many of the rules set out by Leonhardt [1] and continues
to be a spectacle at night becoming a tourist attraction as
well as a transportation device. The Bridge appears to be
well maintained and should continue to serve without
requiring large scale repair for many years to come.
The construction process was quick and relatively
problem free. The methods had been tried on previous
projects (First Severn Crossing) and have, due to their
success, been carried forward onto many more
constructions since.
8 Acknowledgements
This paper could not have been completed without
the assistance of Sian O’Keefe at Hyder Consulting who
has provided vital information.
9 References
[1] Leonhardt F. 1982. Bruecken/Bridges. Deutsche
Verags-Anstalt.
Fig 5.19 The finished bridge during the day [3]
[2] BS 5400-2:2006. British Standards Institute.
6 Future Requirements
[3] The Sheridan Group. The Bosporus Bridge. L. Bell &
Co. Ltd.
6.1 Introduction
[4] Wow Turkey website – Night Photographs
http://wowturkey.com/forum/viewtopic.php?t=4552
&start=120
It is difficult to predict the usage a bridge will get
especially when there is no method of dry transport and
therefore the Bosporus Bridge was designed to be flexible
in terms of traffic movement. Some lanes are reversed in
peak flow to cope with the demand and extra lanes,
originally for emergency vehicles are sometimes used in
peak traffic. Pedestrians have been prevented from
walking across the bridge making it solely a transport
bridge for vehicles.
The high demand for a road crossing meant that
Freeman Fox & Partners were again commissioned by the
Turkish government to building another road crossing
over the Bosporus, The Fatih Sultan Mehmet Bridge was
completed in 1988 with a similar design to alleviate the
congestion and spread the demand of the First Bosporus
Bridge. Istanbul is the largest city in Turkey and is still
[5] BS 5400-3:2000. British Standards Institute.
[6] Ibell T. Bridge Engineering. Department of
Architecture and Civil Engineering, University of
Bath
[7] Highways Agency. 1996. The Appearance of Bridges
and Other Highway Structures. Chapters 8 and 22.
The Stationary Office. ISBN 011 5518045.
[8] Ray S.S. Barr J. Clark L. 1996. Bridges – Design for
Improved Buildability. CIRIA Report 155.
[9] Highways Agency. 1998. Design Manual for Roads
and Bridges - Design and Appearance of Bridges.
The Stationary Office. ISBN 011 5520287.