Abstract: In order to reinforce a working hull, such as the fuselage of an aircraft and in particular that of a helicopter, a frame (C) is embodied made of a composite material in the form of a monolithic monobloc structure. This structure is constituted by a profile whose internal flange (16) and the external half-flanges (18) principally comprise unidirectional fibers which extend over its entire length. As a variant, the lower section of the frame is embodied separately in the form of a panel bordered over its entire periphery by lateral half-flanges which also principally comprise unidirectional fibers. After assembling the two sections of the frame, the half-flanges are then opposite each other in the elongation.