DISCUSSION THREAD
Hints:
Write down the stiffness matrix [K] using the elemental contributions, as well as the forcing vector {F} from the work expression. Enforce the displacement boundary conditions on the stiffness matrix and forcing vector. Solve for the nodal displacements.
Any questions? Ask (and answer) questions here.
Once I have found the displacements for C and D? What is the approach for finding the reactions. According to the boundary conditions, we defined these reactions as 0.
The displacements at C and D are zero, as you describe; however, the reaction forces required for constraining the displacements of these two points are not zero.
As described in lecture, the equations needed for determining the reaction forces are embedded in the FE equations: [K]{u} = {F}. Take a look at Example 17.5 on pp. 17:21-22. Near the end of the solution, you will see that the reaction forces are found from the first and fifth FE equations (prior to the enforcement of the boundary conditions). That is the process that you should also follow in this problem.