Elastomeric bearings (reinforced rubber) C.M.M. EB
EB (Elastomeric Bearings) is the series of structural rubber bearings designed and manufactured by C.M.M.
The EB supports are made up of a series of vulcanized rubber layers with steel plates that have the function of increasing the resistance of the support to instability in the face of high vertical loads.
The ability to move horizontally is guaranteed by the shear deformation of the rubber layers: for this reason every movement imposed on the support causes a horizontal load of elastic response, a consequence of the horizontal rigidity of the device. In the same way, every horizontal load imposed on the support (wind, seismic forces, braking, etc.) generates a horizontal deformation of the rubber layers and therefore a displacement of the deck.
The structure designer can therefore use this type of structural support only if he accepts that the lateral loads imposed on the deck (action of the wind, earthquake, braking), can cause a rigid displacement of the same, and that the impressed displacements cause a force of elastic recall.
In the figure below is depicted, in a schematic way, the behaviour of the bridge beam subjected to thermal expansion or imposed forces and of the elastomeric support that allows such expansions deforming in shear.
The EB supports are made up of a series of vulcanized rubber layers with steel plates that have the function of increasing the resistance of the support to instability in the face of high vertical loads.
The ability to move horizontally is guaranteed by the shear deformation of the rubber layers: for this reason every movement imposed on the support causes a horizontal load of elastic response, a consequence of the horizontal rigidity of the device. In the same way, every horizontal load imposed on the support (wind, seismic forces, braking, etc.) generates a horizontal deformation of the rubber layers and therefore a displacement of the deck.
The structure designer can therefore use this type of structural support only if he accepts that the lateral loads imposed on the deck (action of the wind, earthquake, braking), can cause a rigid displacement of the same, and that the impressed displacements cause a force of elastic recall.
In the figure below is depicted, in a schematic way, the behaviour of the bridge beam subjected to thermal expansion or imposed forces and of the elastomeric support that allows such expansions deforming in shear.
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Rotation is allowed by deformation by crushing the support.
The EB supports are available in various types (EB-B, EB-C1, EB-C2, EB-C3), which differ from each other due to the presence, shape and arrangement of the external anchor plates.
The EB supports are also available in fixed, guided or multidirectional bearing modes with PTFE (teflon):
EB-R fixed bearings: prevent movements along any direction in the plane thanks to external lateral restraints arranged in both directions to receive side loads.
EB-G guided bearings: movement capacity in one direction only, guaranteed by external lateral guides
EB-M multidirectional bearings: equipped with a PTFE (teflon) plate applied by vulcanization to the upper surface of the elastomer to obtain a multidirectional slide that allows the displacements in front of the sole friction resistance of the PTFE shoe (<3%).
The main features are:
The EB supports are available in various types (EB-B, EB-C1, EB-C2, EB-C3), which differ from each other due to the presence, shape and arrangement of the external anchor plates.
The EB supports are also available in fixed, guided or multidirectional bearing modes with PTFE (teflon):
EB-R fixed bearings: prevent movements along any direction in the plane thanks to external lateral restraints arranged in both directions to receive side loads.
EB-G guided bearings: movement capacity in one direction only, guaranteed by external lateral guides
EB-M multidirectional bearings: equipped with a PTFE (teflon) plate applied by vulcanization to the upper surface of the elastomer to obtain a multidirectional slide that allows the displacements in front of the sole friction resistance of the PTFE shoe (<3%).
The main features are:
- Vertical load up to 15000 kN at the Ultimate Limit State (SLU)
- Horizontal load up to 20% of vertical load (except for fixed or guided bearings, which can withstand higher loads)
- Possibility of equipping the supports with negative vertical load capacity (up-lift), both in service conditions and in the Ultimate Limit State
- Maximum displacement capacity in every direction of the plane equal to the total height of rubber (according to European standard EN 1337-3)
- Maximum rotation up to 0.01 rad (usually 0.005 rad)
- Durability medium / high (all external components in steel are covered with a protective anti-corrosion paint) and require little maintenance
- Temperature range: -40 ° C ÷ + 50 ° C
- The supports can be designed and installed on any type of structures
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