RC slab interaction with truss chrords

[Anonymous]

I am modelling a building that is predominately steel framed.

The floor plate structure consists of composite concrete floor slabs that are supported on steel secondary beams that span onto steel primary beams. In some cases floor slabs are supported by storey deep steel trusses that are located around the perimeter of a floor plate and also cut across a floor plate.

I am modelling the building using Robot Structural Analysis 2015 and I am modelling the building in 3D.

When I model the floor slabs as meshed floor slab elements in Robot I find that the floor slab significantly interacts with the chords of the steel trusses - see attached screen shot, image furthest to left for example. For conservatism of the steel design I do not want the slab to interact with the truss chord, so that the truss chord sees the full tension or compression force.

Please can you tell me how to prevent axial forces generated in the truss chords from interacting with the RC slab.

I am considering an approach where I model the diaphragm action of the RC slabs using steel cross bracing that is tuned to achieve the same diaphragm stiffness as the RC slab. In this way I can use the 3D model to calculate overall building lateral sways. Following this I can reduce the bar axial stiffness of the cross bracing so that there is minimal interaction with the truss chords and use this adjusted model for calculating element forces in the trusses. Is this a suitable approach to use?

Thanks,

David