Here is a three part series of videos, that describes topology optimization of a beam subject to three point bending, the beam is modeled in 1D, 2D and 3D in each part respectively.

The author of these videos is Manuel Ramsaier (Ravensburg Weingarten University)

3 Point Bending Beam + Topology Optimization – Part 1: 1D Modeling

3 Point Bending Beam + Topology Optimization – Part 2: 2D Modeling

3 Point Bending Beam + Topology Optimization – Part 3: 3D Modeling