Abstract: A stiffened part formed from at least two members of thermoset composite material including at least one body of a first structure and optionally a second structure. A manufacturing method includes: forming a fibre preform and impregnating each body of the first structure with thermosetting resin or forming a pre-impregnated fibre preform to obtain a body formed from uncured thermosetting composite material supported by a mandrel; optionally partially or fully polymerising at least one body supported by a mandrel; optionally, providing the second structure formed from uncured, partially uncured or fully uncured thermosetting composite material; optionally, depositing a layer of uncured thermosetting adhesive on an area where a fully cured member makes contact with another member of the part; joining the members, each member being juxtaposed with; or stacked upon, at least one other member; fully curing the assembly by heat treatment; removing the mandrel from each fully cured body.