Memorandum

TO:	All Design Section Staff
FROM:	J. Kapur
DATE:	February 25, 2002
SUBJECT:	LRFD Seismic Design

Adequate “seat widths” and “longitudinal restrainers” shall be provided at all intermediate expansion bearings of multi-span WSDOT bridges.  The design of seat widths and longitudinal restrainers shall comply with the requirements of the AASHTO LRFD Specifications article 4.7.4.4 and 3.10.9.5 respectively.  The seat widths and longitudinal restrainers shall be capable of accommodating all longitudinal movements.

 Background:

The AASHTO LRFD Specifications article 3.10.9.1 makes the need for longitudinal restrainers optional if adequate seat width at expansion bearings of multi-span bridge is provided in accordance to the specifications.  Although the primary defense against unseating of bridges at expansion joints is to provide adequate seat width, WSDOT will continue to provide longitudinal restrainers at the intermediate expansion joints of all new bridges as a secondary measure to address potential unseating.  Longitudinal restrainers shall not be used at the end piers (abutments).

 If you have any questions regarding these issues, please contact Tim Moore at 705-7163 or Bijan Khaleghi at 705-7181.

 JK:dsb

BK

 cc:      J. Weigel – 47340
           F. Higgins - 47340