شناسایی آزمایشگاهی ترک‌ طولی تراورس بتنی پیش‌تنیده با استفاده از تست مودال تجربی

Ballasted railway tracks are considered one of the significant transportation systems for passengers and goods in the country. Prestressed concrete sleepers play a critical role in the safety and stability of ballasted tracks as one of the primary components of the railway infrastructure. However, during the operation of railway tracks, the performance of sleepers is affected by various types of damage. Longitudinal cracking, caused by environmental or chemical factors and exacerbated by dynamic loads, has been mentioned as one of the most important types of sleeper damage in technical literature and industrial reports. Therefore, longitudinal cracks are one of the most significant damages that appear due to tendon corrosion inside the concrete sleepers. Nevertheless, limited studies have been conducted on identifying this cracking in concrete sleepers, so, an applied study that can provide additional information for inspectors or engineers to quantify the health status of sleepers is highly required. Hence, this paper focuses on experi-mental investigations on the identification of longitudinal damages in concrete sleepers due to tendon corrosion using changes in measured vibration characteristics in modal testing.
For this purpose, laboratory specimens of B-70 concrete sleepers were examined in healthy and dam-aged with longitudinal cracks under various conditions. The detection of damage was carried out by identifying the longitudinal cracks in the central upper and lower locations, as well as on one and/or both lateral faces with a length of 120 centimeters. The results of the measured experimental modal tests showed that in all specimens, the mode shape and natural frequency of the first vibration mode could not identify longitudinal cracks in concrete sleepers. Furthermore, changes in the characteristics of the five and above modes also did not show significant differences in their health status, and they could be disregarded in the identification of longitudinal damage in concrete sleepers. Additionally, the results indicated that the natural frequencies of the second to fourth modes (first to third flexural modes) in the longitudinal cracking of sleepers decrease by up to 30 percent. Moreover, sleepers with longitudinal cracking in the upper and lower locations on both lateral faces have about a 55 percent greater impact on reducing dynamic characteristics compared to the sample with similar conditions and longitudinal cracking in the lower side, which can be useful in the evaluation of the severity of the longitudinal cracking in concrete sleepers.