RATIR (The Reionization and Transients Infrared Camera/Telescope) is an optical infrared camera in the 1.5 m telescope in the Mexican National Astronomical Observatory, OAN, in San Pedro Martir, Baja California. The primary goal of RATIR is to remotely observe Gamma Ray Bursts as detected by the SWIFT satellite. This document describes the problem definition, the mechanical calculations, the conceptual design, the finite element analysis, the different configurations proposed and the mechanical performance of the main Support Structure and Dichroic Mounts for RATIR.