Experimental determination of Paris law coefficients for modeling the process of corrosion-fatigue destruction of reinforced concrete railway bridges superstructures

The variability of natural and man-made factors and the complexity of reinforced concrete calculations make the problem of estimating the service life of reinforced concrete bridges spans multifaceted and complex. Along with this, the construction of the Moscow – St. Petersburg high-speed railway has started in Russia, which makes the problem of the durability of reinforced concrete bridge spans even more actual. Fulfilling the requirement of SP 453.1325800 to ensure a service life of 100 years is currently difficult for the designer to achieve, just as there are no ways to verify compliance with this requirement. Reinforced concrete bridges under HSR conditions will be subject to significant dynamic impacts, which, together with an aggressive environment, can significantly reduce the service life of the structure. This article discusses corrosion-fatigue durability as one of the aspects of the method for predicting the service life of a bridge, taking into account the dynamic load. This type of degradation of reinforced concrete is caused by the combined action of pitting corrosion of reinforcement and cyclic loading, which leads to the initiation and growth of a fatigue crack in the reinforcing bar.Methods of calculating the time of crack growth in reinforcement up to the critical value are analysed, Paris law is highlighted as widely used in fracture mechanics. The problem of applying Paris law lies in the empirically determined material coefficients. Literature analysis shown that coefficients can depend not only from type of material but from specific alloy as well. The task was set to conduct an experiment to determine the coefficients of Paris's law for reinforcing steel grade 25G2S, which is widely used in bridge superstructure. The test was carried out using a vibrating machine and reinforcement samples with an initial stress concentrator. Based on the results of the experiment, the coefficients of the Paris equation were determined for reinforcing steel 25G2S, which will make it possible to use them in the methodology for predicting the development of fatigue cracks.

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