Memorandum

The live load distribution factor for the exterior girder of beam-supported slab bridges shall be as follows:

• For exterior girder design with a slab cantilever length equal to or less than one-half of the adjacent interior girder spacing, use the live load distribution factor for interior girder. Note: The slab cantilever length is defined as the distance from the centerline of the exterior girder to the edge of the slab.
  
• For exterior girder design with a slab cantilever length exceeding one-half of the adjacent interior girder spacing, use the lever rule with the multiple presence factor of 1.0 for single lane to determine the live load distribution. The live load used to design the exterior girder shall never be less than the live load used to design an interior girder.
  
• The special analysis based on the conventional approximation of loads on piles as per AASHTO-LRFD Article C4.6.2.2.2d shall not be used unless the effectiveness of diaphragms on the lateral distribution of truck loads is investigated.

If you have any questions regarding these design issues, please contact Bijan Khaleghi.

CCR:bk

cc:     J. Weigel, 47340

         F. Higgins, 47340