<p>According to the invention, this piece comprises: a base section piece (1) provided with a projecting longitudinal heel (4) delimiting a longitudinal groove (7); a longitudinal pyrotechnic cord laid in said groove; and a plurality of consecutive section piece portions (2) fixed one after the other to said base section piece (1) by first fixing means (9). Between the consecutive section piece portions (2) are second fixing means (18), distributed along said base section piece (1) and independent of said first fixing means (9), enabling said pyrotechnic cord to be fixed and positioned relative to said base section piece (1).</p>
