In Timoshenko beam theory the shear strain mentioned as (dw/dx)+Ф for mathematical convenience . Why can't we use with (dw/dx)-Ф?

While reading FEM by J .N Reddy I have notice that the shear strain term is taken as sum of (dw/dx) and Ф for mathematical convenience. I didn't understand why we should take slope in negative...

22 November 2019 2,295 2 View