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TO: All Design Section Staff
FROM: J. Kapur
DATE: June 18, 2001
SUBJECT: Shear Design

The following modifications shall be applied to the shear design provisions of the AASHTO-LRFD
Bridge Design Specifications article 

1.   The numerator of equations 1, 2 and 3 shall be changed to: 

        Mu/dv + 0.5Nu + (Vu-Vp) - ApsFpo

 2.    The flow chart of figure C5. shall be replaced with the flow chart in the attachment.


Recent extensive comparisons with the experimental data by Professor Michael Collins from the University of Ontario and the author of the Modified Compression Field Theory for shear design of concrete members, indicate that eliminating the term 0.5Cotq did not result in loss of accuracy. 

 The multiplier of 0.5Cotq in the numerator of equations 1, 2 and 3 requires assuming a value for the angle q and often requires performing several iterations. The revised form of equations 1, 2 and 3 eliminates the need for q angle iterations.  The revised flow chart indicates the elimination of q angle iterations.

 If you have any questions regarding this design issue, please contact Bijan Khaleghi at 705-7181.




             cc:        J. A. Weigel, Bridge and Structures - 47340
                        E. H. Henley, Bridge and Structures - 47340
                        H. L. Coffman, Bridge Preservation - 47341
                      F. Higgins, Bridge and Structures - 47340
                        R. Lewis, Construction - 47354
                        Z. Fahoum, Bridge and Structures – 47340