Bearing Supports on Structures – Simple Design and Uses of Elastomeric Bearing

Bearings are support items used in absorbing the stress effects from a bridge or building structure. Elastomeric bearings fall under bridge bearings, and there are a wide variety of these used for various applications.  There are a lot of bridge bearings that are similar to these, such as neoprene bearings and laminated elastomeric bearings, and these are commonly used in the construction industry.  Various standards dictate the manufacturing and design of these bearings, in order to ensure robust performance, longevity and reliability.

These bearings are used to deal with a variety of conditions relating to steel structures, which include movement as a result of expansion or contraction due to temperature flux, shrinkage of the structure, the strain of tensioning, or movement of the earth.  They are commonly used as part of the construction of buildings with steel frames and also for bridges, and are designed to minimise resistance resulting from movement within metal or steel frames, and function as structural bearings.  The distinctive low friction characteristics of polytetrafluoroethylene (PTFE) are utilised to increase the tractability and strength of rubber.

Bearings are useful for

  1. Supporting bridges for traffic loads
  2. Resistance of earthquake forces on bridges
  3. Resistance of earthquake forces on buildings
  4. Creation of damping effect on various types of structures
Photo showing animation of pendulum bearings used on a building to withstand the effects of an earthquake

The following are some basic instructions for design of a bearing and the plinth:

  1. Estimate the strain on the bridge beam or structure due to shrinkage, creep, temperature movement and other factors
  2. Estimation of the minimum pad thickness of the elastic material of the bearing
  3. Calculation of the area of the proposed bearing to withstand the load from the bridge or structure using the pressure capacity of the estimated pad thickness
  4. Selection of a suitable dimension of the elastomeric bearing

Useful codes include, BS 5400, EN1337-3

The following is an animation of earthquake response of a multistory building with installed bearings at the substructure interface:

References:-

  1. Elastomeric Bearings, Applications and Types of Elastomeric Bearings – http://www.technoslide.com/articles/et30-elastometric-bearings.html
  2. Freyssinet Sustainable Technology – http://www.freyssinet.com/freyssinet/wfreyssinet_en.nsf

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