Shear Distribution Factor 2

[blocjoe]

I am in the process of rating a bridge and wanted to know the method of computing the shear distribution factor. The AASHTO LFD code says that both shear and moment distribution factors are the same and to compute both from Table 3.23.1, but I have seen in the software manual that the shear distribution factor is computed differently. Could anyone please explain the method for computing the shear distribution factor or any thoughts on this issue.

Joe

 

[Qshake]

Usually, the end shears and reaction distribution factors are calculated based on simple span distribution. See article 3.23.1.2.

The article goes on to say that for wheels in other positions on the span (e.g. midspan) the distribution for shear shall be determined by the method prescribed for moment.

This is logical in that near the support, shear displacement will be more influential than the flexural displacement. For example consider a short cantilever subjected to a point load and a long cantilever subjected to the same point load. The percentage contribution of the shear displacement to the short cantilever is likely to be as much as 50% whereas for the long cantilever the shear contribution probably won't reach 0.5%.



Regards,
Qshake

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[jike]

Spangler did some research at the University of Iowa on this subject. The title of his paper is "The Distribution of Shearing Stresses in Concrete Floor Slabs under Concentrated Loads". I have found it to be useful.