Experimental investigation of the stress-strain state of steel-reinforced concrete span structures of a railway bridge under different conditions of composite action between structural elements

Purpose. The purpose of this study was to experimentally investigate the stress-strain state of steel-reinforced concrete span structures of a railway bridge, taking into account different conditions of the composite action of the bridge structural elements under loading from freight and passenger trains. Methodology. The research methodology involved measuring fibre stresses and deflections in the structures of a steel-reinforced concrete railway bridge, both in a span structure without defects and in a bridge span structure with defects that disrupt the composite action of the structural elements under normal operating conditions. The measurements were performed using a Spider-8 analogue-to-digital data acquisition system during the passage of freight and passenger trains hauled by a VL11-series electric locomotive. Findings. The test results of the steel-reinforced concrete bridge span structures showed that the reinforced concrete ballast trough slab in the damaged span was subjected to tensile stresses, with fibre stresses reaching 6.55 kg/cm², whereas compressive stresses of −26.75 kg/cm² occurred in the undamaged bridge span. This provides unequivocal evidence that the ballast trough slab of the defective span was completely excluded from composite action with the upper flanges of the main steel girders. At the same time, the results of the measurements of span girder deflections showed that, during the passage of a freight train hauled by VL11 locomotives, the maximum deflection of the defective span structure reached 17.48 mm, which was 3.6 times greater than the deflection of the undamaged span structure, amounting to 4.85 mm. During the passage of a passenger train hauled by a VL11-series electric locomotive, the maximum deflection of the defective span structure was 15.91 mm, compared with 4.25 mm for the undamaged span structure. These results demonstrate the irreversible changes in the static behaviour of the damaged span and substantiate the need to impose train speed restrictions on the bridge. Originality. For the first time, experimental data were obtained on the stress-strain state of steel-reinforced concrete span structures of a railway bridge under different conditions of composite action of the bridge spans subjected to loads from freight and passenger rolling stock. This made it possible to assess the static behaviour of the damaged bridge span and substantiate the need to limit train speeds on the bridge. Practical value. The practical significance of the study lies in obtaining objective scientific data to substantiate major repair works and develop technical solutions for connecting the ballast trough slab blocks to the steel girders of the defective span structure, based on the results of the conducted inspections and experimental tests.