AASHTO-LRFD Steel Reinforced Elastomeric Bearing:

AASHTO-LRFD Steel Reinforced Elastomeric Bearing tutorial is about design method B. It is needed to know shape factor,material properties, stress limits, shear deformations and also stability of bearings.First of all, we needed to know, steel reinforced elastomeric bearings shall consist of alternate layers of steel reinforcement and elastomer bonded together. Elastomeric bearing may contain external steel load plates either or both at upper and lower elastomer layers. Also, all internal layers shall be of the same thickness. The top and bottom cover layers shall be no thicker than 70 percent of internal layers. Furthermore, tapered elastomer layers shall not be used.

Secondly, shape factor of a layer of an elastomeric bearing shall be taken as the plan area of the layer divided by the area of perimeter free to bulge. ( Article 14.7.5.1).

Moreover, elastomers are flexible under shear and uniaxial deformation, but they are very stiff against volume changes. The shear modulus of the elastomer at 23 C shall be used as the basis for design. Specified shear modulus of elastomer must be between 0.60 and 1.30 MPa. ( Article 14.7.5.2). Also, shear stiffness of an elastomer is very important because it affects the amount of force transfered from superstructure to substructure.

Furthermore, the maximum horizontal displacement of a bridge superstructure shall be taken as 65 percent of the design thermal movement range combined with movements caused by creep and shrinkage.

Also, the minimum thickness of steel reinforcement shall be 1.6 mm.

Finally, deflection due to instantaneous live load must be smaller than 3.2 mm. ( Article 14.7.5.3.6)