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TO: All Design Section Staff
FROM: Chuck Ruth
DATE: January 10, 2000
SUBJECT: Reinforced Elastomeric Bearing Pad Shims

This memorandum reminds bridge designers that internal shims of steel reinforced elastomeric bearing pads shall comply with the ASTM A 570 Grade 36 (A 570M Grade 250) Specification [Steel, Sheet and Strip, Carbon, Hot Rolled, Structural Quality].

WSDOT Standard Specifications Section 9-31 references the AASHTO M 251 Specification [Plain and Laminated Elastomeric Bridge Bearings]. The M 251 specification, in turn, requires ASTM A 570 steel shims. ASTM A 570 is produced in seven grades corresponding to yield stresses ranging from 30 ksi to 55 ksi. In the past, whenever designers have not specified a grade on the contract plans, the bearing pad manufacturer typically has used Grade 30 or 33. This is unconservative when design calculations are predicated on a yield stress of 36 ksi.

An amendment to Section 9-31 of the Standard Specifications has been submitted to obviate any ambiguity by specifying ASTM A 570 Grade 36 (A 570M Grade 250) as the base material for steel shims. This amendment will also bring the shim clearance requirements of Section 9-31 into conformance with the clearance requirements stated in Section 8.4.3.D.5.a. of the Bridge Design Manual.


cc:     J. A. Weigel, Bridge and Structures - 47340

         Lewis, Construction, Bridges - 47354

         R. Higgins, Bridge and Structures - 47340