The present invention relates to a post comprising a hollow elongated body (1) and rods (2) adapted for static cooperation therewith and so interconnected that said cooperation is interrupted when the post is subjected to local transverse stresses of a predetermined magnitude.The novel features of the invention reside in that the hollow body (1), which is manufactured by extrusion, is provided with a number of per se known internal grooves (5) forming rupture lines and, at least two inwardly open channels (8) defined by inwardly projecting tongues (7), and in that the rods (2) are accommodated in the channels (8), suitably under prestress.