A stiffening assembly comprises a bulkhead including an inner surface shaped to define a central lumen, an outer surface surrounding the inner surface, and a wall connecting the outer and inner surfaces and shaped to form a plurality of holes spaced apart and surrounding the lumen. The stiffening assembly also comprises a plurality of longitudinal beams, each longitudinal beam extending through a corresponding hole of the plurality of holes. The stiffening assembly also comprises a clamping assembly configured to contact the plurality of longitudinal beams. The stiffening assembly is adjustable between a flexible state in which each longitudinal beam is movable within the corresponding hole of the plurality of holes and a stiffened state in which the clamping assembly clamps the plurality of longitudinal beams against the bulkhead such that transfer of shear forces between the plurality of longitudinal beams and the bulkhead stiffens the stiffening assembly.
