bridge bearings and stability

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					    BRIDGE BEARINGS AND
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    STABILITY
     INTRODUCTION

    FUNCTIONS OF BEARINGS
    DESIGN CONSIDERATIONS
    TYPES OF BEARINGS AND THEIR FEATURES
    CERTAIN SPECIALLY DESIGNED BEARINGS
    PROTECTION AGAINST CORROSION
    COMPREHENSIVE LABELLING
    CONCLUSION
    REFERENCES



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     Bridge engineers today usually do not design bearings,
       Because of the variety of bearings generally available.
     The engineers detail only the loading conditions and
      describe the bearings in terms of performance
       specification.
     The design is done by the bearing manufacturer itself.
     For many years, design horizontal bearing loads have
      been much smaller than design vertical loads (typically
       horizontal loads 10%-20% of vertical loads).




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     Now    with the increase of Multi-span redundant
      structures, as well as increased understanding of the
      behavior of structures, it is becoming more common to
      see design horizontal loads equal to or greater than
      design vertical loads.
     This increase in horizontal force will affect the stability of
      the structure.
     Stability is not a design element normally associated
      with bridge bearings, it implies Equilibrium of bearing or
      structure under all load condition.
     Today’s bridge bearings are resisting high horizontal
      loads-so stability demands close attention.



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     In the standard highway bridge configuration, the
     superstructure rests on the substructure and the
     connection between the two elements is the bearings.
     Any load that must be transferred from the
     superstructure to the substructure must be transferred
     through the bearings.
     The bearings must transfer horizontal forces due to
     wind, seismic, and live loads & also it should minimize
     secondary forces such as those caused by rotations,
     temperature variation, shrinkage, sliding or rolling
     and creep.

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    The functions of each bearing type are:
     Elastomeric :-
    i.    allows the deck to translate and rotate,
    ii.   resists loads in the longitudinal, transverse and
         vertical directions.
    iii. accommodated by elastomeric pad.
     Plane sliding :-
    i.    low    friction   polymer,    polytetrafluoroethylene
         (PTFE), sliding against a metal plate is for
         accommodating constant displacement.
    ii. does not accommodate rotational movement in the
         longitudinal or transverse directions
    iii. only resists loads in the vertical direction.
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     Roller :-
    i.    Large longitudinal movements can be accommodated
          by these bearings,
    ii.   but vertical loads only can generally be resisted.




          figure(a)           figure(b)            figure(c)

    Fig (a) represent Elastomeric bearing , Fig (b) represent
    Plane sliding bearing , and Fig (c) represent Multiple Roller
      bearing.


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    The designer has to assess the maximum and
     minimum loads that the deck will exert on the
     bearing together with the anticipated movements
     (translation and rotation).

     Bearing manufacturers will supply a suitable
     bearing to meet the designers requirements.




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      EQS BRIDGE BEARING
      POT BEARING
      BRIDGE BEARING - DISK
      BRIDGE BEARING - SPHERICAL
      BRIDGE BEARING - HDB
      BRIDGE BEARING - DOUBLE SLIDING EQS
      HORIZONTAL LOAD BEARING




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     EQS BRIDGE BEARING




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           NAME           MATERIAL          KEY
                                            FUNCTIONS

                                            1.Accommodating
                                            vertical load

     1        Disk          Polyurethane    2. Accommodating
                                            rotative distortion



     2     MER Spring       Polyurethane    Constant horizontal
                                            force resistance



     3   Friction plate
         for base
                           Fluoro resin plate
                          (PTFE)              Accommodating
         isolation                          constant
                                            displacement.


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           NAME         MATERIAL KEY
                                 FUNCTIONS




         Shearing pin   High strength    Transfer horizontal
     4                  steel material   load.


                                         1.Protect main
                                         material of bearing
     5   Guide box      Steel material   support
                                         2.MER spring
                                         expansion
                                         resistance.


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     Features:-
         Applicable to all bridges with small , medium and long
         spans. Particularly good applicability to bridges with
         small and medium spans.
        Due to the energy absorption bearing that is able to
         absorb and dissipate most of earthquake loads.
        As MER and Disc made of polyurethane are not
         sensitive to temperature compared to rubber, it keeps
         good applicability even in area with large temperature
         difference yearly.
        Durability was proved by experience of installation for
         a long time and various testing .
        Maintenance is very simple.

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      Pot Bearing is a bridge bearing which is used mostly in the
       world.
      Arrangement of components in this bearing is properly
       done, so they are more efficient.
      They safely delivers both vertical and horizontal force of
       superstructure to pier
      Accommodates rotative displacement with compression of
       rubber plate
      Accommodating horizontal displacement of superstructure
       according to temperature change

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     Product features:-
      The optimum design based on external force and

       construction conditions

      Easy installation

      Easy movement

      Easy identification and replacement worn-out and

       damaged parts

      Easy replacement at the time of maintenance




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     * This is a product equipped with excellent durability

       and outstanding earthquake-proof capability.

     * Its critical parts are applied with polyurethane.




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          NAME               DESCRIPTION
     Fluororesin plate   Inducing more smooth
                         sliding or movement.

 Guide block             This is a device limiting
                         moving direction of bridge
                         superstructures.
 Polyurethane disk       A device supporting bridge
                         superstructure load and
                         accommodating rotative
                         strain.
 Shearing pin            A device that delivers load
                         of horizontal direction.

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     Features and Benefits
      Small sized bearing.
      Excellent durability.
      Convenience in maintenance.

      The most economical bridge bearing support : It

       keeps the best economy among all bridge bearing
       support for earthquake-proof .This is due to the fact
       that application of polyurethane disk of high elasticity
       and high strength.


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      Delivers loads of superstructure and also absorbs

       strain and movement of superstructure.

      It is suitable for all types of bridges including steel

       bridge, concrete bridge, skew bridge and curved
       bridge.

      It reflects earthquake-proof design with outstanding

       durability.


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     Air
     pocket
     rubber




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      Excellent resistivity against impact.

      Superior durability as no strain is generated even
       when applying loads three times of design load
      Preventing cracks developing in bridges

      This bearing can also used in bridges in cold
       areas(below zero to -50°C).
      They are also suitable for structures with high loads
       and frequent displacements.

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      Hydampot Bearing – HDB

      This is a device with E-type steel material damper installed
       at specially designed pot bearing.
      Under normal condition ,it accommodates
       vertical/horizontal load displacement and rotative
       displacement.

      And at the time of earthquake, it dissipates excessive
     loads and displacement by safely delivering only a part of it
     to substructure.
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      Main body is the specially-designed pot bearing that

      is suitable for long span structure .

      Very economical substructure design is possible as it

      absorbs and dissipates more than 70% of horizontal
      loads such as impact load(earthquake, sudden
      braking of railway vehicles).




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     BRIDGE BEARING – DOUBLE SLIDING EQS

     o DSEQS, Double Sliding Earth Quake System

     o A type that is, compared to conventional EQS

       products constructed for sliding to occur on one
       surface , this is improved for the sliding to occur on
       both upper and lower surfaces simultaneously.




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          A d v a n ta g e s

     I.    Resist horizontal loads.
     II. Support     loads of superstructure and
           accommodate rotational movement




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       HORIZONTAL LOAD BEARINGS
      It is designed to absorb horizontal loads in one or
       more directions.
      This type of bearing can be used with laminated
       elastomeric bearings or free sliding pot bearings.
      In this configuration, laminated elastomeric bearings
       and / or pot bearings support the vertical load, while
       horizontal load bearings restrain lateral horizontal
       loads.

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     TWO TYPES OF HORIZONTAL LOAD
     BEARINGS
      Fixed pin type         Guided type
      Restrain horizontal    Allow movement in
      movement in all         one direction and
      direction               restrain movement
                              in other




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     •Horizontal load bearings are installed by means
      of different type of fixing system , like tag plates,
       removable or fixed anchor bars




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     CERTAIN SPECIALLY DESIGNED BEARINGS




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     Pot Bearings with Shock transmission
      devices                   POT bearing coupled
                                   with ST fluid shock
                                   transmission unit
                                   This combination can
                                   resist both static and
                                   dynamic loads.
                                   ST reacts dynamic loads
                                   due to earthquake, wind,
                                   braking, etc.




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     Bearings with horizontal elastic
      stiffness
                               To provide an elastic
                              horizontal response.
                              This elastic response in
                              the horizontal direction
                              (one or two directions)
                              can be useful for
                              minimizing or to
                              equalize the horizontal
                              forces acting on
                              bearings.


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     Bridge Bearings with uplift restraints
                               The bridge bearings
                               with uplift
                               restraints are
                               normally used when
                               they are requested
                               to resist not only to
                               standard positive
                               vertical loads but
                               also to
                               occasional negative
                               loads.

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Bearing with vertical load measurement
 Bearing can be equipped with a
 system to measure the vertical load
 acting on the bearing. It can be useful
 to verify the effect of transient loads
 on bearings(example traffic on
 bearings) or to check the structure
 behaviour in case of foundations
  settlements.
 The load measurement can be placed
  near the bearing.




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     BEARING WITH ANCHOR PLATES/SLIDING
     SURFACE
                                Bearings can also
                                be produced with
                                special anchor
                                plates or
                                with sliding
                                surfaces to
                                improve the
                                structure's
                                displacement
                                capacity. This kind
                                of bearing can
                                withstand vertical
                                loads of up to
                                12,000 kN.
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     CORROSION PROTECTION

     Steel components exposed to the elements are
      protected against corrosion.
     Corrosion protection in accordance with the
      aggressiveness of the environment in which the
      bearings are to be installed and each customer’s
      requirements.



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  The High resistant corrosion protection (Metallization)

     is as follows
     - Sandblasting to SA 2.5 grade
     - Metal spraying to 85µm w ith

       Zn/Al = 85/15
     - Sealing: Epoxy sealer 15-25µm
     - Top coat: Epoxy paint 100µm




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      COMPREHENSIVE LABELLING
       All bearings with external steel plates are
       provided with a metal label detailing the
       properties of the bearing:
       - bearing type
       - maximum vertical and horizontal loads
       - rotation
       - order number
       - date of manufacture
       - and reference



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     CONCLUSION
     Bearings must first be designed and detailed to meet
     required vertical and horizontal load capacities, rotation
     limits, and anchor bolt clearances,
     A stability check should be done.
     As designers, we need to be aware of the potential
     problems involved, ie type of earthquake expected,
     type of structure, nature of underlying soil,& finally
     structure’s maximum permissible movement.
     After considering all the above ,a correct selection of
     bearing can be done.

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     REFERENCES
      Drew E.Gilstad, Bridge Bearings and stability, Journal of
         structural Engineering, Volume 116,Issue5, pp. 1269-
         1277(May 1990).
        Rangwala, Bridge Engineering, S.B.Patel charotar
         publishing, 8th edition ,2004.
        ASCE Research library.
        http//www.ec21.com/product-details/bridge-bearing-EQS-
         3624486.html
        http//www.search-docs.com/bridge-bearings-and
         stability.pdf.html
        http//www.scitation.aip.org
        http//www.ecooo.com/admin/document/elastrometric%20
         bridge%20bearings.pdf
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