bridge bearings
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Bridge BearingsTRANSCRIPT
11/14/2015 Bridge Bearings
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Bearing Design Standards
Bearing Design Standards Eurocodes • BS EN 1337: Structural Bearings • PD 6703:2009 Structural Bearings Guidance on their use British Standards • BS 5400: Part 2: Specification for Loads • BS 5400: Part 9: Code of Practice for Design of Bridge Bearings Design Manual for Roads and Bridges • BD37: Loads for Highway Bridges • BA42: The Design of Integral Bridges • BD20: Bridge Bearings, Use of BS 5400 Part 9
Choice of Bearings
Bridge bearings are devices for transferring loads and movements from the deck to the substructureand foundations.In highway bridge bearings movements are accommodated by the basic mechanisms of internaldeformation (elastomeric), sliding (PTFE), or rolling. A large variety of bearings have evolved usingvarious combinations of these mechanisms.
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Elastomeric Bearing
Plane Sliding Bearing
Multiple Roller Bearing
Design Considerations
The functions of each bearing type are :
a. ElastomericThe elastomeric bearing allows the deck to translate and rotate, but also resists loads in thelongitudinal, transverse and vertical directions. Loads are developed, and movement isaccommodated by distorting the elastomeric pad.
b. Plane SlidingSliding bearings usually consist of a low friction polymer, polytetrafluoroethylene (PTFE),sliding against a metal plate. This bearing does not accommodate rotational movement in thelongitudinal or transverse directions and only resists loads in the vertical direction. Longitudinalor transverse loads can be accommodated by providing mechanical keys. The keys resistmovement, and loads in a direction perpendicular to the keyway.
c. RollerLarge longitudinal movements can be accommodated by these bearings, but vertical loads onlycan generally be resisted.
The designer has to assess the maximum and minimum loads that the deck will exert on the bearingtogether with the anticipated movements (translation and rotation). Bearing manufacturers will supplya suitable bearing to meet the designers requirements.
Bearings are arranged to allow the deck to expandand contract, but retain the deck in its correct positionon the substructure. A 'Fixed' Bearing does not allowtranslational movement. 'Sliding Guided' Bearings areprovided to restrain the deck in all translationaldirections except in a radial direction from the fixedbearing. This allows the deck to expand and contractfreely. 'Sliding' Bearings are provided for verticalsupport to the deck only.
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Bridge Components
David Childs B.Sc, C.Eng, MICE
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