Design of R.C.C. cantilever beams, is based on the resultant force at

The correct answer is Option A: Fixed end
Here's why:

A cantilever beam is a beam that's fixed at one end (the fixed end) and free at the other end (the free end).

Think about it like a diving board. The part attached to the pool deck is the fixed end, and the end you jump off is the free end.

When a load is applied to a cantilever beam, the maximum bending moment (the force that causes bending) and shear force (the force that causes sliding) occur at the fixed end.

Therefore, the design of a reinforced concrete cantilever beam (R.C.C.) is primarily based on these maximum forces at the fixed end to ensure it can withstand the load without failing.

* Free end: The bending moment and shear force are typically zero at the free end.
* Mid span: The bending moment and shear force are present at the mid-span, but they're not the maximum values that the beam needs to be designed for.
* Mid span and fixed support: While both locations experience forces, the fixed support is where the maximum forces are concentrated.