1. I noted your persistence on the forum, by waiting help on your problem – that seems now as not being the structural one but a mathematical one (?).

2. Seeing that during a previous exchange, I proposed to you a transparent and robust solution for your case – the dichotomy – that converge very well, I wonder why your perseverance on Newton-Raphson?

3. Starting from the assumption of “why not?” I propose to you, in the following, some comments.

4. The Newton Raphson suppose the use of the derivative of the function f(x) - the object of solution finding - I note that your f(x) function contains the "min(a;bb))" function. This function has no treatment in the SMath derivation procedure, that’s (IMHO) the main reason for your problems. However, seeing that under the min function there is a constant, that derived gives zero, you can produce externally the derivative. So, you can apply simply the Newton Raphson.

5. In order to make a more robust your solution finding process, I propose to make your f(x) parametric, by dividing it by b*h*fcd.