  We consider a plate made from an isotropic but brittle elastic material,
which is used to span a rigid aperture, across which a small pressure
difference is applied. The problem we address is to find the structure which
uses the least amount of material without breaking. Under a simple set of
physical approximations and for a certain region of the pressure-brittleness
parameter space, we find that a fractal structure in which the plate consists
of thicker spars supporting thinner spars in an hierarchical arrangement gives
a design of high mechanical efficiency.
