For the structure shown below, cross$-$section at A is of interest. End D is loaded. Using the

coordinate system shown in the figure, there are generally three internal forces $(F_x,V_y,V_z)$

and three internal moments $(T_x,M_y,M_z)$ at A$.$

$(1)$ Cut the structure imaginatively at A and draw its the free body diagram

$(2)$ Find $F_x,V_y,V_z,T_x,M_y,M_z,$

$(3)$ Explain what loading modes $($axial$,$ shear, torsion, bending$)$ exist at A$.$