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The steel structure (E=200GPa) shown in Figure 4, is a hollow shaft (AD) with the length of b=500mm is built-in (fixed) at one end (far left, A) and connected to the arm CD at the right end, D. The hollow shaft has an outside diameter d=50mm and the wall thickness is 5mm (leaving the inner diameter of 40mm). The arm CD (L=400mm) is assumed to be safe. The load P, applied to the arm at C in negative y direction, is 5kN. Also a 10kN load is applied to the shaft at D in positive x direction. Answer the following questions: a) Identify the values and senses (directions) of all internal forces and moments acting on the section at the wall (Built in end) and show them in a sketch on the section alongside the coordinate axes (x, y, and z). (6 marks) b) Based on findings in part a, explain why the wall section is the weakest section of the shaft and why point A (top of cross section at wall) is the weakest point of the structure. (3 marks) c) From the above, calculate stresses due to bending moment, axial force, torque (twisting moment), and shear force acting on point A. Show the stress state on an infinitesimal at A (clearly indicate the axes and the view point). (6 marks) d) Stress state at the weak point of a structure is given as o, -200 MPa (compressive), oy = + 200 MPa (tensile), and y=-100 MPa. Show the stress state on an infinitesimal. Using both the analytical (formulae) and graphical (Mohr's Circle) approaches, find principal stresses and their orientation, and maximum shear stress and its orientation. On Mohr's circle, clearly show the principal and Max shear stresses, and their corresponding angles (orientations). (6 marks) e) From findings in part d (above), calculate the safety factor of the structure using both Tresca and von-Mises failure criteria, assuming that the structure is made of a steel with yield strength of 500MPa. Comment on the results (clearly explain and justify the difference in answers obtained from the two theories). (4 marks) Point forces: 5kN at C in (-y) direction; 10kN at D in (+x) direction Figure 4. Sketch of the structure showing details of geometry and loading Total: (25 marks)