The hollow, closed-section beam structure is made from two

aluminum channels with Ga= 3.75-10 psi and two horizontal

titanium plates with G= 6.25-106 psi. The dimensions are: a

= 1.0in, ta = 0.1 in and tr= 0.2in. A torque 7: = 1000/bf-in is

applied at the cross section of the beam as shown. Obtain:

a) Am- an area enclosed by the median line,

b) shear stress in aluminum channel and in titanium plate,

c) the value of J for the composite cross-section,

d) the angle of rotation per unit length for the composite cross-section.