Caltrans Bridge Design Practice Chapter 21 Abutment Shear key design

[jy4661]

On Caltrans Bridge Design Practice 4th Edition Chapter 21 page 21-96, the calculation of effective width bv for Vww showed the superstructure depth (6.75') plus 1/3 of the abutment stem height (7.25'). Could you explain why 1/3 of the stem height was used instead of full height of the abutment stem wall?

Thank you a lot.

 

[ernestog84]

That example is lacking several figures to help visualize the problem. I took a look in the Seismic Design Criteria (where the equation is being pulled from) and it is also not very clear.