The magnetic bending of muon tracks for the ATLAS Muon Spectrometer is prov
ided by the large air-core toroid magnets. The Barrel Toroid structure, nam
ed the warm structure, is an open structure inside which the muon chambers
are installed. The physics performance of the muon spectrometer imposes str
ingent requirements on the design of the warm structure. It should support
the muon chambers with required precision and stability, the deformation of
the structure must be minimised. At the same time, the quantities of the m
aterials used in the structure must also be minimised. Through extensive st
ructural analyses, the design optimisation has been achieved to fit with th
e physics requirements. This paper gives an overview on the design consider
ations of the warm structure. (C) 2001 Elsevier Science B.V. All rights res
erved.