Long-term investigations of dynamic behavior of a pre-stressed concrete ballasted railway bridge

Dynamic properties of civil structures such as natural frequencies, damping ratios, and mode shapes are essential parameters for evaluating the health condition of structures. However, dynamic properties are prone to be biased by environmental effects which may lead to fault structural health assessment. To investigate the environmental effect on the dynamic parameters of ballasted bridge, in this paper, a series of vibration experiments were performed on a multi-span pre-stressed concrete beam railway bridge. The dynamic properties of the bridge were identified and analyzed. In total, 9 experiments were conducted in 2 years. In the first 8 experiments, only sleepers and tracks had been removed. For the last experiment, the bridge was under destruction. The subsidiary components of the structure were destructed, and some holes were drilled on the slab for hoisting. The results show a clear seasonal variation in natural frequencies that in winters the natural frequencies reach local maximum values. Damping ratios show no clear variation regularity, indicating the complex correlation between the damping ratios and the environmental variation. Additionally, compression tests of concrete pieces of the slab were also conducted to investigate the degradation of material properties. The result of the compression tests indicates that there is approximately no degradation of compression strength of the concrete slab after the bridge was in service for several over 4 decades.