Avaliação de danos em dormentes de concreto protendido por meio da técnica de análise modal

Abstract

Prestressed concrete sleepers are essential components of railway superstructures, responsible for maintaining track gauge and transferring loads from the rails to the ballast. During service life, these elements may be affected by different damage mechanisms, including central cracking associated with deficient support, cracking at the rail seat, and deterioration caused by internal expansive reactions. Although visual inspection is widely used, it has limitations in detecting internal damage or cracks partially closed by prestressing. In this context, this study evaluated the application of experimental modal analysis as a complementary non-destructive diagnostic tool for prestressed concrete sleepers. Three damage mechanisms were investigated: central cracking due to center bound, cracking at the rail seat, and cracking induced by alkaliaggregate reaction. The sleepers were subjected to controlled damage induction, visual and physical crack characterization, and modal testing using impact hammer excitation. Natural frequencies, damping ratios, and mode shapes were evaluated for the first three vibration modes. The results indicated that the first flexural mode provided the most consistent response among the parameters assessed. For center bound damage, the natural frequency showed a progressive, although limited, reduction with increasing damage level. For rail seat cracking, the damping ratio was more sensitive than the natural frequency. In sleepers subjected to expansive reaction, the natural frequency was influenced by the interaction between initial stiffness gain due to continued hydration and progressive stiffness loss caused by expansive cracking, whereas damping showed a more direct response to the evolution of deterioration. The results indicate that modal analysis has potential to complement the diagnosis of prestressed concrete sleepers, provided that it is interpreted together with the physical characterization of damage, visual inspection, and identification of the active deterioration mechanisms.