Influence of prestressed state of the span on vibrations of a reinforced concrete railway bridge during an earthquake
Abstract
This paper deals with the peculiarities of calculating the seismic resistance of reinforced concrete railway bridges based on real earthquake records. Using finite element and finite difference methods, the problem is discretised by taking into account the interaction between the foundations of the bridge piers and the ground according to the Winkler model and the prestressing of the span structure. The prestressing of the span is provided by the stressed elements of the working reinforcement. The coefficients of the interaction stiffness matrix are calculated from the areas of the contact surfaces of the suspension piles with the soil. The example of calculation of a three-span reinforced concrete railway bridge for real seismic effects of earth-quakes shows the influence of the prestressed state of the span during an earthquake. The 53.2 m long railway bridge is located in the area of 7points in seismic intensity between Shavat – Gurlen stations, which is located on the railway section Shavat – Gurlen – Jumurtau – Kipchak – Koibakli. Numerical solution of the problem of earth- quake resistance of the bridge shows the change of its stress – strain state in time. The results of calculation of the railway reinforced concrete bridge are obtained on the basis of real records of earthquake “Boshroyeh” (Iran) with intensity of 7 MSK-64. According to the calculation results, we conclude that the normal stresses in the spans, without taking into account prestressed reinforcement, become tensile from the bottom side. Since the tensile strength of concrete is poor, it causes gradual cracking of the span, resulting in a shorter span life. According to the obtained results, without prestressing the reinforcement of the railway bridge, the calculated values were higher than the tensile stress values allowed by the normative documents by 0.45 MPa. Taking into account the prestressing of the reinforcement, the stress values corresponding to those accepted in the normative document were obtained.