Proposed Test Method for Center Bound Risk Assessment: A Case Study

The center bound condition in railway sleepers results from loss of support at the ends and concentration of reactions in the central region, altering stress distribution and generating a characteristic cracking pattern, with direct impact on structural safety margins. A case in Brazil, associated with lateral ballast insufficiency, motivated the need for a methodology capable of reproducing, in a controlled and traceable manner, the support uncertainty observed in the track and enabling comparison of damage signatures under different scenarios. This study proposes an experimental methodology to evaluate the sensitivity of damage to variations in the effective central support length. A dedicated test setup was developed to reproduce centralized support and to allow controlled variation of support width in four configurations: 5  cm, 20  cm and 60 cm . Nine prestressed concrete sleepers were tested, with three specimens per configuration, up to failure. At each 15 kN load increment, the cracking pattern was mapped and the opening of the first crack was measured, enabling tracking of damage progression and establishing experimental indicators comparable across support conditions. The results show variations in first-crack load, crack pattern evolution, and ultimate load as a function of effective support length. The developed setup and associated procedure establish an experimental basis linking support condition to damage signature, enabling inference of the presence and progression of center bound in the investigated case and characterization of structural vulnerability to support variability. As an outcome, a methodological tool for risk assessment was delivered to the railway operator, consisting of a reproducible test protocol, damage indicators, and a comparative reference database to support inspection, diagnosis, and maintenance decisions when the occurrence of center bound is uncertain.

Keywords: Center bound, Prestressed concrete sleepers, Experimental test setup.