R R/ R R (i) Initial choice (ii) Alternative A (iii) Alternative B the stages of deformation, and the corresponding evolution of the shear stress, in the solid circular shaft as the applied torque is increased towards its ultimate value. [8 marks] A thin-walled hollow circular tube (Figure Q4b) with mean radius R and uniform (b) wall thickness of t has been suggested for the construction of a prefabricated steel structure of a building. As part of design modification to simultaneously reduce the maximum shear stress and the angle of twist per unit length, it has been proposed that the circular tube be replaced. Two options have been put forward: a R by R square hollow tube and an equilateral triangular hollow tube with a side length R, similar to those shown in Figure Q4b. All the three tubes are made from the same material, have equal uniform wall thickness 1, and subject to the same magnitude of torsional load. If the design aim is to minimise both the maximum shear stress and the angle of twist per unit length, which of the three tubes would you recommend for the construction? Use detailed calculations to justify your answer. assumptions made. State any [12 marks]