$14\mathrm{.}1.$ A square slab measuring $3m$ on each side is simply supported on three sides and unsupported along the fourth. It is reinforced for positive bending with an isotropic mat of steel providing resistance $m_n$ of $9\mathrm{.}5kN-\frac{m}{m}$ in each of the

two principal directions. Determine the uniformly distributed load that would cause flexural failure, using the method of virtual work.