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Bridge Design & Assessment

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Wherever possible slender piers should be used so that there is sufficient flexibility to allow temperature, shrinkage and creep effects to be transmitted to the abutments without the need for bearings at the piers, or intermediate joints in the deck.
A slender bridge deck will usually look best when supported by slender piers without the need for a downstand crosshead beam. It is the proportions and form of the bridge as a whole which are vitally important rather than the size of an individual element viewed in isolation.


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Different Pier Shapes


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Different Pier Shapes


Design Considerations

Loads transmitted by the bridge deck onto the pier are :

  1. Vertical loads from self weight of deck
  2. Vertical loads from live loading conditions
  3. Horizontal loads from temperature, creep movements etc and wind
  4. Rotations due to deflection of the bridge deck.

The overall configuration of the bridge will determine the combination of loads and movements that have to be designed for. For example if the pier has a bearing at its top, corresponding to a structural pin joint, then the horizontal movements will impose moments at the base, their magnitude will depend on the pier flexibility.
Sometimes special requirements are imposed by rail or river authorities if piers are positioned within their jurisdiction. In the case of river authorities a 'cut water' may be required to assist the river flow, or independent fenders to protect the pier from impact from boats or floating debris. A similar arrangement is often required by the rail authorities to prevent minor derailments striking the pier. Whereas the pier has to be designed to resist major derailments. Also if the pier should be completely demolished by a train derailment then the deck should not collapse.
 

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Bridge Components