1) Decide if you want to model this with beam elements, shell elements or solid elements. Create Geometry in SpaceClaim for the Length and cross-section of the beam. Draw only half the length to use symmetry at the center. 

2) In Mechanical, create a Symmetry Region at the center and select the geometry at the center. Make sure to set the Direction normal to the plane.

3) Create a Translational Joint at the other end to compress the beam.

4) Add a tiny side force to the geometry at the center to seed the deformation.

5) Add a Joint load, type=Displacement.  Type in a number that is 2% of the length.

6) Under Analysis Settings, turn on Auto Time Stepping. Make the Initial, Minimum substeps 100 and the Maximum substeps 200 and turn on Large Deflection.

7) Solve.