The SDD and SSD support structure for the ALICE Inner Tracking System

The ALICE Inner Tracking System is designed to provide the determination of the primary vertex and of the secondary vertices in order to reconstruct charm and hyperon decays, particle identification and tracking of low-momentum particles and to im prove the momentum and angle measurements of the Time Projecting Chamber (TPC). The device consists of six layers of silicon detectors and has been installed into the ALICE's cavern of the LHC accelerator. In this paper we describe the mechanical structur e of the instrument and its behaviour during and after the assembly procedure.