$6\mathrm{.}42.$ The two$-$cell, thin$-$walled beam section of Figure P$6\mathrm{.}42$ is loaded by a torque $T.$ Find the location and magnitude of the maximum shear stress and the torsional stiffness $K$ for the section. The wall thickness is everywhere equal to $t.$ Compare your results with those obtained when there is no internal partition, as in Figure P$6\mathrm{.}28.$

Figure P$6.42$

${}_{\text{m}\text{a}\text{x}}=0\mathrm{.}13\frac{T}{a^2}t,K=6\mathrm{.}4a^{3}t.$