AASHTO-LRFD Elastomeric Bearing Types:

AASHTO-LRFD Elastomeric Bearing Types tutorial is about bearings.

Firstly, bearings are used to transfer superstructure loads to substructure. Bearings are must be able to withstand and transfer dynamic forces. Also bearings result vibrations without causing any serious damage on substructure. There are two bearing categories according to restriction of movement as;

  • expansion and,
  • fixed.

Bearings can be fixed in one direction and expansion in the other direction or both directions. Expansion bearings allow for rotational movement and longitudinal movement for expansion and contraction of the spans. Fixed bearings act as hinges by allowing for rotational movements but preventing longitudinal movement.

Furthermore, designers most commonly use elostomeric bearings. Elastomeric bearings are fabricated either as plain bearing pads or as laminated ( steel reinforced ) bearings.

  • Plain bearing pads consist of only elastomer.
  • Laminated bearing consist of elastomer and alternate layers of steel reinforcement bonded together.

Elastomeric bearing pads are used in relatively small bridges compare to laminated elastomeric bearings. Elastomeric bearings have less vertical load, translation and rotation capacities compared to laminated elastomeric pads. The reason for this is that plain elastomeric bearings are weaker and more flexible. Because plain elastomeric bearings are restrained from bulging by friction alone.

Finally, in design of elastomeric bearing types, AASHTO uses two design methods Method A and Method B. Moreover, Method A is specified in Article 14.7.6 and Method B as specified in 14.7.5. Method A gives lower capacity compare to Method B. Since Method B results in higher capacity, it requires additional testing. Large steel reinforced elastomeric bearings are thicker than 200 mm or have a plan area greater than 645 160 mm2 . Since possibility of failure is more in large bearings and Method B requires additional testing, designers would use Method B to design large steel reinforced elastomeric bearings