I have recently switched from experimental structural engineering to more theoretical subjects (mechanics) and that is why my question may sound simple to you.
My question: How can I expand values of the approximation below in series form in vicinity of points $ r = R+h $ and $ z_0 = t_3$?$$ K_{rr} = σ_{rr} \left(1 + \frac{\partial u_r}{\partial r} \right) + σ_{rz} \frac{\partial u_r}{\partial z}. $$ It will help me a lot. Thank you.