DISTRIBUTION FACTOR-BRIDGE DESIGN

[Plainsboro]

when we design stringers for bridge as per AASHTO, depending upon the spacing of stringers, we calculate the distribution factor to be multiplied with load to obtain required design data to design stringers. Does any one has idea that why this Dist. factor is different for moment and shear.To me this number only tells how much portion of load a stringer will take and than we can calculate max shear and moment. so # should be same?
Also anyone has idea that why skewed bridges are weak in shear?

 

[tincan]

Many years ago, B.C. (before computers)the distribution for shear was the same as the distribution for moment, excepting for the end reactions. The 60's AASHO (not AASHTO)standard specifications book was a fifth of the size of the current standards. Research is the result of many of the changes, although they carry many of the new factors out to the 6th decimal place.
Best, Tincan.

 

[yakpol]

Plainsboro,
Different distribution factors for shear and moment reflect location of the vehicle in the span to maximize the forces. For maximum shear truck is located close to the end of the girder (small distribution length - larger distribution factor), for maximum moment in midspan (smaller distribution factor). If to look for moment and shear in midspan then moment distribution factor is the correct for both.