Impact of low frequency dynamic loading on structural health of existing reinforced concrete railway retaining walls in the foothills of the Carpathians

Abstract

SUMMARY This study aims to develop an inspection method of a structural health of the existing railway retaining walls (RRW) in the conditions of natural and technogenic dynamic loadings. Local seismological station registers nearly 110–130 seismic events per year. 70–80% of the above events occurs within 100 km radius and are of 2–4 earthquake intensity. Applicability of the nondestructive methods for the evaluation of structural health of existing retaining wall is examined by conducting a large number of the nondestructive tests on retaining walls at the site. It was found from the series of experimental test that the vibration tests were effective in evaluating the characteristics of dynamic properties of the retaining walls, which were affected by structural health of the retaining walls. Nondestructive evaluation of the reinforced concrete RRW has been measured with high accuracy the natural frequency and it is used for the evaluation of the structural health of the retaining walls. This method was based on the knowledge that the natural frequency of the RRW decreased with the damage of the structures and increased with the reinforcement. Natural frequency of the RRW is evaluated by carrying out a spectrum analysis using measured free vibration, which is recorded by velocity sensors. Free vibration was induced by transport movement or natural seismic activity in the foothills of the Carpathians. Based on the site test, it was found that the percussion test and vibration test using the spectrum as an index could be applicable for the condition rating of existing RRW. Assessment of failure probability of the RRW is doing in different conditions in different diagnostic stages and on basis of limited information need for accept of administrative decision: “to continue building operation or not”. This result indicated that the small-scale vibration tests could be applicable to evaluate the structural health of the existing Ukrainian retaining structures (RRW). Registered vibrate-acceleration maximum amplitude of the RRW under the influence of micro-seismic vibrations and moving trains does not exceed 0.0025m/c2 along the X axis and 0,008 m/c2 along the Z axis. The strength of concrete conforms to the class B25. The results of calculations show the corresponding natural frequency oscillations - 9.46 Hz. The difference with the experimentally registered frequency is 1.46 Hz, what corresponds to the deviation of ∼ 18%.