(Solved): For the following structure, using the unit load method which is based on the principle of virtual ...

For the following structure, using the unit load method which is based on the principle of virtual work, determine (1) the rotation at point $D$, (2) the relative rotation between point $\mathrm{C}$ and point $\mathrm{D}$, and (3) the horizontal displacement at point $\mathrm{C}$. (Note: Neglect shear deformation and axial deformation in each member.) Young's modulus: $E$, Second Moment of the Cross-Sectional Area: $I$