This report aims to resume the analysis done during my internship at Dassault Systèmes, in the CATIA Composite Team. The main objectif of my internship was to validate the 1DBeam command of the Stiffened Structure concept app: a command that allows to reduce an elongated 3D component into a 1D one (called 1DBeam). The main components used to test this command were some masts of some sailing boat, made of composite materials. So, this report will contain a first introduction to Dassault Systèmes, to its apps and to my team. After it, there will be some bibliographical introductions to Composite Materials, to Finite Element Models, and also to sailing masts, in order to understand how the laminates are distributed inside it.