Reinforced Elastomeric Bridge Bearing Pads

 

Rubber used in the composition of bearings can be either natural or NR for "Natural Rubber" or synthetic, in which case the compound is generally a chloroprene polymer poly-chloroprene or CR for "Chloroprene Rubber".

The minimum thickness of a sheet, in accordance with EN 1337-3, may in no circumstance be under 5 mm, or over 25 mm.

 

AssaFlex Bearing Pads are designed for use in Bridges and other structures such as Buildings as a vertical load bearing component.  They are manufactured from high quality materials with number of layers of steel plates depending on the type of bearings highly strong and extremely resistance to weathering, ageing with almost no influence from UV radiation and Ozone.  Sheets of high strength steel are capsulated by Elastomer either NR or CR type.

AssaFlex Bearing Pads are manufactured to international standards such as European EN1337-3,

British BS 5400, German DIN 4141, American AASHTO    ,etc

Every component is manufactured, moulded, mechanically worked and assembled by fully qualified operatives in our factory under strict ISO 9001:2008 certified quality control standards.

 

Imam· khomeini Bridge - Esfahan IRAN

Technical Features:

 

Description

A laminated elastomeric bearing is a "block of vulcanized Elastomer (…) reinforced internally by one or several steel plates, chemically glued (bonded) during vulcanization. (…). Elastomer is a macromolecular material that regains its shape and initial dimensions approximately after being submitted to significant deformation under the influence of a low stress variation".

External Forces being supported

Elastomeric bearings permit the simultaneous support of the following loads:

v  Standard absorption of vertical loads

v  Absorption of briefly applied external horizontal forces

v  Horizontal movement in all directions through shear deformation

v  Rotation of the bearing surfaces around all axes

NON-REINFORCED ELASTOMERIC BEARINGS ELASTOMERIC

At AssaFlex we manufacture Non reinforcement Bearings (Type F)to your details.  This type of bearings is robust and more cost effective in comparison, where a strip rubber to a specific measurement can carry compressive loads while at the same time providing transitional and rotational movement.  This type is not suitable for bridges.

 

We produce the pads according to your design for the type of application you require.

LAMINATED ELASTOMERIC BEARINGS

Neoprene Bearing Pads provide a uniform transfer of load from beam to substructure. They permit beam rotation at the bearing point due to deflection or misalignment. They absorb vibration and prevent sound transfer, while reducing the destructive action of vibration between movable and stationary structural members. They also provide for movement caused by normal expansion and contraction and concrete creep effects & shrinkage. Neoprene Bearing Pads are used extensively in bridge structures.

Natural rubber (with the appropriate formulation) provides good resistance to traction, excellent failure strain and performs well with dynamic loads and in the cold, although it does tend to crystallize. On the other hand, it is highly gas permeable, its resistance to oils and solvents is quite poor and its susceptibility to aging must be compensated by the use of antioxidant and anti-ozone6, where by polychloroprene which, among other qualities, provides excellent resistance to aging, a very low load-bearing creep rate and good tear resistance. This makes it perfectly suitable for the requirements of bearings.

 

 

The characteristics of internal plates

The thickness of the plates must equal or be above 2 mm. S235 steel must be used or steel with an equivalent failure strain.

The characteristics of external plates

For type C bearings, the thickness of the external plates is 15mm for elastomeric laminations with a thickness of 8 mm and under, and 18 mm for thicknesses above. S235 steel or an equivalent is also used.

The characteristics of slide plates

The characteristics of sliding planes as in EN 1337-2, Sliding systems generally consist of a stainless steel plate lying on a side of the bearing on which a poly tetra fluoro ethylene

(PTFE) sheet is bonded these are type D and E bearings.

 

Types of Bearings

Type & transition bands

Bearing types are determined under a certain design criteria. In the table below by using AASHO-LRFD Bridge Design Specification, we have established the transition band between the changes in the specification. This work had been carried out only for Rotations of ≤0.005 & ≤0.015. Table A1 & A2.
The resulting design will provide the geometry and other pertinent specifications for the bearing. It is likely that one or more of the preliminary selections will be eliminated in this step because of an undesirable attribute. The final selection should be the bearing system with the lowest combination of first cost and maintenance costs as indicated in Table A. If no bearing appears suitable, the selection process must be repeated with different constraints.
The most likely cause of the elimination of all possible bearing types is that a mutually exclusive set of design criteria was established. In this case the basis of the requirements should be reviewed and, if necessary, the overall system of superstructure and bearings should be re-evaluated before repeating the bearing selection process.

 

 

Bearing Pad Selection Diagram

 

 

 

 

 

 

Laminated Elastomeric Bearings (LEB) and Pot Bearings (PB) represent the bigger percentage of bearings used around the world.

Laminated Elastomeric Bearings

Type A: Single reinforcement. Bearing  (Not used in civil Engineering structure)

Type B: The definition for type B according to EN 1337-3 is; this type has (n+1), reinforcement / metal and (n)elastomeric of constant thickness with perimeter at least 4 millimetres thick and the upper and lower faces with a nominal 2.5mm thickness of elastomeric.  The tolerance is (-0 and +2)

Other Type B: By definition these are different in that the upper and lower elastomeric coatings are thicker.  This type of bearing is no longer straightforward reinforcement protected by elastomeric, but designed on the basis of required ability such as Elastomeric a Half Lamination or Passive Coating types

Type C: Elastomeric bearings with two external plates and threaded holes for use on metal structures, or as an anti-lift device; in this latter case, suitable anchor bars must be fitted to the bearings for anchoring purposes.

 

Type D:. Elastomeric bearings with external plates and pins that connect to suitable steel plates in order to secure the bearing to the structure.

Type E: Elastomeric bearings with two suitably etched external plates to facilitate the bearing's bonding to the structure by way of vulcanisation.

 

 

Type F:Non reinforced or strip bearing (Not used in Civil Engineering Structure)

Sliding Bearings: in cases where there is significant horizontal displacement, in particular on the abutments, the number of laminations required for these deformations risks being incompatible with the buckling stability of the bearing or in the case of a very flexible support. In these cases, sliding bearings may be required instead of ordinary bearings.

 

Bearing With Steel Guide

Elastomer friction bearing support, which is executed as a fixed point by means of steel guides

Free Sliding Elastomeric Bearing

Friction Bearing designed as a free sliding bearing in longitudinal and transversal direction.

A virgin PTFE layer is bonded to the rubber to reduce the friction coefficient with the stainless steel welded to the top steel plate.

Elastomer friction bearing support

Installed as a fixed bearing in a longitudinal or transversal direction.  This is done by way of steel guides, where a large range of movement is required.   To achieve this, a PTFE layer is bonded to the Rubber/Elastomer to reduce the friction coefficient with the stainless steel welded to the top steel plate

Circular Type

Circular shape with similar characteristic elastomeric bearings

ü  Circular Type with outer fixing steel plate

Two external steel plates can be vulcanised directly onto elastomeric bearings with simple reinforcement during production, so securing the bearings to the structure with mechanical fastenings and reducing the risk of slippage.

POT BEARINGS

This type of bearing may be considered the most important one from the commercial point of view, since the pot bearings represent the largest portion of the bearings market in the world.

Pot bearings consist of an elastomeric pad confined in a steel cylindrical pot by means of a close fitting piston and an internal seal. They can be combined with a sliding element in to accommodate translational movements in one or any direction.

The most important detail of the pot bearings is the seal, preventing the leakage of the Elastomer / rubber through the gap between pot and piston and governing the durability under repeated rotations.

Pot bearing and pot bearing combined with sliding surface and guide

SPHERICAL AND CYLINDRICAL PTFE BEARINGS

Cylindrical bearings consist of a backing plate with a convex cylindrical surface (rotational element) and a backing plate with a concave cylindrical surface between which a PTFE sheet and the mating material form a curved sliding surface. Cylindrical PTFE bearings are also used in combination with flat sliding elements and guides to form free or guided bearings.

Spherical PTFE bearing consist of a backing plate with a convex spherical surface (rotational element) and a backing plate with a concave spherical surface between which a PTFE sheet and the mating material form a curved sliding surface.

Types of spherical PTFE spherical bearings

a)      Fixed By sliding surface

Fixed spherical bearings may transfer the horizontal forces through the curved surface and in that

case consist of two plates with one interposed sliding surface (see Fig a).

b)      Fixed By restraining Ring

In alternative way they may transfer the horizontal forces through a restraining ring and in that case they consist of three plates with two sliding surfaces, one curved and one flat (see Fig. b).

c)       Free sliding in any direction

Spherical PTFE bearings are also used in combination with flat sliding elements to form free sliding bearings (See Fig. c).

d)      Guided by Internal Guide

In combination with flat sliding element and guides to form sliding guided bearings. The guide may be internal and in that case the horizontal forces are transferred through the spherical surface In that case the horizontal forces are subject to limitations given by the stress distribution on the PTFE surface, (see figure d).

e)      Guided by External Guide

In alternative, for greater level of horizontal forces, the use of two external guides is preferred (See Fig. e).

 

Quality Control:

Bearings are important elements of structures, such as bridges and viaducts, ensuring that they operate correctly. The durability of the structure depends on their quality, as they are in a constant state of use.

The life expectancy of bearings is the result both of their intrinsic qualities and of the care taken over

The quality of these products depends on expertise in the manufacturing process. Quality Assurance provisions should enable you the client to:

ü  Convey the quality required in terms of manufacturing methods

ü  Obtain the quality required

ü  Check that it has achieved the quality required

ü  Justify subsequently that it has been reached and checked.

ü  AssaFlex products are checked independently at certain intervals such as Esfahan’s Polytechnics or other reputable laboratories.

CE Marking

Quality control procedures will be implemented in the factory such as:

ü  Tests on samples taken in the factory in accordance with a prescribed test programme.

ü  Inspection of the ecstatic of the products

CE marking will be then placed on the products.

The last stage before leaving the factory is vacuum packed on palletized items.