milau viaduct

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    1.GENERAL INTRODUCTION :

    The Millau Bridge or Viaduct as it should technically

    be known as provides the final missing link in the A75 auto route ultimately connecting Paris to

    Barcelona Prior the viaducts construction traffic would have had to descend the Tarn Valley

    causing a bottle neck in the town of Millau especially during the summer months of !uly and

    August The multi"span cable stayed bridge passes over the Tarn valley at its lowest point

    between two plateaus #n order to do this it had to become the tallest road bridge in the world

    creating the world$s tallest bridge piers standing at %&%m' the structure rising to (&(m at the top

    of the pylon The bridge also holds the title of the world$s longest multi"span cable stayed bridge

    with a total length of %&)*m There is a slight gradient of (+ from ,orth to -outh as well as a

    slight curve about a radius of %*'***m The piers are of post tensioned reinforced concrete and

    the deck and pylons are of steel

    -everal initial proposals were at first considered by -.T/A 0the

    1rench 2ighway 3epartment4 in linking the e isting auto routes to the north and south of the

    Tarn Valley These included the idea proposed by initially by bridge designer Michel Virlogeu

    This included a route that would partially descend the valley' cross the Tarn with a 7**m span

    cable stayed bridge and then tunnel through the steeper ,orth side of valley until and 6oining up

    with the auto route 2owever this proposal was to prove too e pensive and too damaging on the

    local environment #n 88* the decision was made to pass the valley at the bridges current

    location with a %5**m bridge Michel Virlogeu proposed a design very similar to the final

    structure consisting of seven main piers with approach piers and a slightly different cable

    arrangement A change in director at -.T/A saw a controlled design competition take place in

    88( to ensure that the best solution was found The only design similar to Virlogeu $s was

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    grant of contract was made in May 88: then in !une %*** the contest for the construction

    contract was launched' open to four consortia #n March %** .iffage established the

    subsidiary Compagnie Efface du Viaduc de Millau (CEVM) and was declared winner of the contest

    and awarded the prime contract in August.

    In initial studies, four options were examined::

    ellow route Black route /ed route Blue route

    FIG(1)

    https://en.wikipedia.org/wiki/Eiffage https://en.wikipedia.org/wiki/Eiffage

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    Great Eastern 0 grand Est 4 0 yellow route 4 passing east of Millau and crossing the valleys

    of the Tarn and 3ourbie on two very high and long bridges 0spans of :** and '*** m or

    %')** and ('(** ft4 whose construction was acknowledged to be problematic This option

    would have allowed access to Millau only from the 9arCac plateau' using the long and

    tortuous descent from 9a ;avalerie Although this option was shorter and better suited to

    through traffic' it did not satisfactorily serve the needs of Millau and its area

    % Great Western 0 grand Ouest 4 0black route4 longer than the eastern option by % km

    07 5 mi4' following the ;ernon valley Technically easier 0re

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    % The low solution' descending into the valley and crossing the river on a %** m 0))* ft4

    long bridge' then a viaduct of %'(** m 07'5** ft4 e tended by a tunnel on the 9arCac side

    3.CONSTRUCTION :

    Two weeks after the laying of the first stone on & 3ecember %** ' the workers started to dig the

    deep shafts There were & per pylon 5 m 0&8 ft4 deep and 5 m 0 ) ft4 in diameter' assuring the

    stability of the pylons At the bottom of each pylon' a tread of (@5 m 0 *@ ) ft4 in thickness was

    installed to reinforce the effect of the deep shafts The %'*** m ( 0%')** cu yd4 of concrete

    necessary for the treads was poured at the same time

    FIG(2)

    #n March %**%' the pylons emerged from the ground The speed of construction then rapidly

    increased .very three days' each pylon increased in height by & m 0 ( ft4 This performance was

    mainly due to sliding shuttering Thanks to a system of shoe anchorages and fi ed rails in the

    heart of the pylons' a new layer of concrete could be poured every %* minutes

    https://en.wikipedia.org/wiki/Larzac https://en.wikipedia.org/wiki/Climbing_formwork https://en.wikipedia.org/wiki/Larzac https://en.wikipedia.org/wiki/Climbing_formwork

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    The bridge deck was constructed on land at the ends of the viaduct and rolled lengthwise from

    one pylon to the ne t' with eight temporary towers providing additional support The movement

    was accomplished by a computer"controlled system of pairs of wedges under the deck the upper

    and lower wedges of each pair pointing in opposite directions These were hydraulically

    operated' and moved repeatedly in the following se

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    Heigh ! "# he $ie%!

    P1 P2 P3 P& P' P P

    8& 5* m

    0( * ft

    * 5 in4

    %&& 8) m

    0:*( ft

    : in4

    %% *5 m

    07%5 ft

    ( in4

    && % m

    0&7( ft

    % in4

    () &% m

    0&&7 ft

    7 in4

    8& m

    0()7 ft

    ( in4

    77 5) m

    0%5& ft

    ) in

    TABLE(1)

    FIG(3)

    A pylon under construction

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    The abutments are concrete structures that provide anchorage for the deck to the ground in

    the ;ausse du 9aCar and the ;ausse /ouge

    3.2 DEC* : The metallic deck' which appears very light despite its total mass of around

    ()'*** tones 0&*'*** short tons 4' is %'&)* m 0:'*7* ft4 long and (% m 0 *5 ft4 wide #t comprises

    eight spans The si central spans measure (&% m 0 ' %% ft4' and the two outer spans are %*&

    meters 0))8 ft4 These are composed of 7( central bo beams' the spinal column of the

    construction' onto which the lateral floors and the lateral bo beams were welded The central

    bo beams have a & m 0 ( ft4 cross"section and a length of 5@%% m 0&8@7% ft4 for a total weight

    of 8* metric tons 088 short tons 4 The deck has an inverse Airfoil shape' providing negative lift in

    strong wind conditions

    3.3 MASTS F

    The seven masts' each :7 m 0%:5 ft4 high and weighing around 7** tones 0)8* long tons 77*

    short tons4' are set on top of the pylons Between each of them' eleven stays 0metal cables4 are

    anchored' providing support for the road deck

    3.& STAYS :

    .ach mast of the viaduct is e

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    water which' in high winds' could cause vibration =dubious – discuss > in the stays and compromise the

    stability of the viaduct

    The stays were installed by the 1reyssinet company

    3.& SURFACE :

    To allow for deformations of the metal deck under traffic' a special surface of

    modified bitumen was installed by research teams from Appia The surface is somewhat fle ible

    to adapt to deformations in the steel deck without cracking' but it must nevertheless have

    sufficient strength to withstand motorway conditions 0fatigue' density' te ture' adherence' anti"

    rutting etc 4 The Gideal formulaG was found only after two years of research

    3.' ELECTRICAL INSTALLATIONS F

    The electrical installations of the viaduct are large in proportion to the siCe of the bridge There

    are (* km 0 8 mi4 of high"current cables' %* km 0 % mi4 of fiber optics ' * km 0) % mi4 of low"

    current cables and (57 telephone sockets allowing maintenance teams to communicate with each

    other and with the command post These are situated on the deck' on the pylons and on the masts

    The pylons' deck' masts and stays are e

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    monitor the reactions of the viaduct to e treme conditions Accelerometers placed strategically

    on the deck monitor the oscillations that can affect the metal structure 3isplacements of the deck

    on the abutment level are measured to the nearest millimeter The stays are also instrumented'

    and their ageing meticulously analyCed Additionally' two pieCoelectric sensors gather traffic

    dataF weight of vehicles' average speed' density of the flow of traffic' etc This system can

    distinguish between fourteen different types of vehicle

    The data is transmitted by an .thernet network to a computer in the #T room at the management

    building situated near the toll plaCa

    3. TOLL PLA+A:

    FIG(&)

    The Dare de pHage 0toll plaCa4

    The only toll plaCa on the A75 auto route ' the bridge toll booths and the buildings for the

    commercial and technical management teams are situated & km 0% 5 mi4 north of the viaduct

    0coordinatesF &&I:J( * K, (I J( 8&K.4 The toll plaCa is protected by a canopy in the shape of a

    leaf 0formed from ten drilled concrete ' using the cr