A fluid solids contacting device comprising a vessel; a first grid assembly section which comprises a plurality of horizontal chords spaced horizontally apart from each other and a plurality of grid platforms inserted between the horizontal chords; wherein each horizontal chord comprises a structural member with sufficient mechanical strength to withstand fluidized forces in the vessel; a plurality of chairs attached to an inside surface of the vessel and spaced circumferentially apart to support the structural member; and wherein each structural member is supported on one or more of the plurality of chairs is provided.