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TO: All Design Section Staff
FROM: Chuck Ruth
DATE: August 1, 1997
SUBJECT: LFD Fatigue Criteria

Per my memo of March 2, 1994, the HS-25 Truck load should be considered as the "design truck" for all new WSDOT bridges. After further discussions with code experts, it has been decided that for steel bridges, the fatigue analysis should be completed using the HS-20 loading. This supersedes my memo of February 5, 1996. This change has been made in recognition that use of the HS-25 loading for fatigue analysis is too conservative.

For all WSDOT steel girder bridges, assume Case I road type when determining the number of stress cycles for design (AASHTO Table 10.3.2A).

Save this memo in BDM Chapter 7 until AASHTO LRFD takes effect.


cc: M. M. Lwin, Bridge and Structures, 47340