The element has an outer shell (6) with an outer contour with channels running parallel to th axis of the central axis of the element. The inner shell of the element has a contour which, in the corner region approaches the outer shell. Both inner and outer shells are joined to one another to form a single unit through a cellular structure which has a series of channels. The cross-section of the corner channels is larger than the other channels. The inner shell has an octagonal cross-section but the outer shell is of quadratic cross-section.
