Hollow structural sections of a circular or polygonal cross section are fixed to assembly elements having a circular or polygonal cross section by means of an end piece fitted into the end of a structural section, a holding cable surrounding an assembly element and a device for tensioning the cable which may be a winding shaft to which one end of the cable is fixed and which may move in a cavity of the end piece between a cable winding position and a position in which the shaft is locked in the cavity. In another embodiment, it is the head of the end piece which is movable with respect to the body of the end piece and which tensions a cable loop of fixed length.