Features of the bridge span performance when shifting the axis of the rail-sleeper grid

Engineering structures form an integral part of the railways, both already operated and yet designed. The joint work of the upper structure of the railway track and the supporting structures of the bridge crossing is an important condition for the normal operation of the railway section without various restrictions and additional work on the current maintenance and diagnostics of structural elements. Presented study is devoted to the investigation of the stress-strain state of a small railway bridge with a beam design, when the axis of the rail-sleeper grid relative to the axis of the bridge is shifted by an amount exceeding the limit value determined by regulatory documents. In the analytical calculation of the behavior parameters and the state of the span under the action of the load, a differential equation is used that describes the vertical vibrations of the beam and allows considering them as a combination of forced and free vibrations. In numerical modeling, the finite element method is used as the solution method, the deter mining equations of which contain linear and angular displacements of nodes of the calculation scheme as unknowns. As a result of the calculations, graphical dependences for normal and horizontal displacements, internal forces, principal and equivalent stresses at various points of the span are obtained. Presented values show an increase in bending and torsional forces, as well as principal stresses when the axis of the railway track is displaced relative to the axis of the bridge. It is noted that although the increase in stresses (by about 6 %) can generally be considered insignificant, the presence of defects in the span beams (concrete chips, cracks in the stretched zone, exposure and corrosion of working reinforcement, decrease in the calculated cross section, leaching of cement stone from concrete, decrease in concrete strength over time) can make it a significant enough factor limiting the operational capabilities of bridge crossings.