Calculation of combined steel-concrete structures shall be conducted in stages. Before monolithic slab concrete gains strength, metal structure is the only structure part that carries loading of its own weight. However, after concrete gains strength, the whole calculated loading is carried by whole reinforced monolithic concrete slab where axis position changes. The article describes main principles of the technique of imaginary hinges installation for the forces calculation in static indefinite continuous structures under conditions of mathematical axis position change in stiffening girder. That enables to simulate the stress-deformation state in the combined structures elements at the initial design stage. This technique is used for the calculation and results analysis for combined structure with composite reinforced concrete top band and steel suspension taking into account of their work stages.

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