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# Plain bearing pad design by AREMA

## Plain bearing pad design by AREMA

(OP)
Good day all.

We are designing a plain (unreinforced) elastomeric bearing pad for a rail bridge according to Chapter 15 of AREMA.
We are able to satisfy 5.5 MPa limit, but we are struggling with GS/k limit.

(1) Is the GS/k limit applicable to plain pads, or is it only for reinforced pads?

The definition of Shape Factor "S" seems to be for reinforced pads, as indicated by the definition of t_sub_i.

(2) For a plain pad, what would t_sub_i be? Is it total pad thickness?

Your help is appreciated. Thank you
Replies continue below

### RE: Plain bearing pad design by AREMA

The AASHTO spec defines "S" as the shape factor for a plain elestomeric pad (PEP), so I would say that you could use the total pad thickness in the shape factor calculations.

Based on what I'm seeing in the AASHTO spec, I would expect the PEP to have a larger value for "k" than for a reinforced bearing. The AASHTO service stress limit is 1.0GS for PEP and 1.25GS for steel and fiberglass reinforced bearings.

### RE: Plain bearing pad design by AREMA

(OP)
Thank you BridgeSmith.

Yes, AREMA uses k = 1.8 for PEP, and k = 1.0 for reinforced bearing.

### RE: Plain bearing pad design by AREMA

Wow, that's much more conservative than AASHTO.

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