This paper presents the seismic analysis of a typical aircraft hangar structure being constructed at Bombay for Indian Airlines Corporation. The main supporting structure has a very heavy mass at the roof level and a few large size columns of height to depth ratio ranging between 2.5 to 4.0. The main objective of this investigation is to study the effect, on the magnitude of seismic forces, of (i) large variation in masses at various floor levels and (ii) inclusion of shear deformation in columns and large moment of inertia of beams in the column region. The results obtained by modal analysis on the basis of recommendations of IS; 1893-1975, are compared for the two cases (a) considering the above referred two effects and (b) neglecting the two effects.