PSI - Issue 84

Mohammad Javad Azari Nezhadian et al. / Procedia Structural Integrity 84 (2026) 1222–1230

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Fig. 7 Primary cracks formed at the sections showing the maximum flexural moment in the simplified analytical model.

It is observed that while both specimens had ductile behavior with quite substantial deformation capacity before failure, one specimen exhibited a slightly more stable post-cracking response, as revealed by smoother attenuation in the load–displacement curve and a comparably delayed onset of crushing at the extrados. On the other hand, the second specimen showed earlier damage localization and a steeper post-peak decline, indicative of lower residual stiffness. This may be due to minor variability in material properties, distribution of rebar, or micro-crack distribution. In light of the above, the integrated assessment of the recorded curves and the observed cracking pattern confirms that both specimens behaved satisfactorily under flexural actions, with significant displacement and crack opening before failure. The ductile post-cracking performance of each specimen shows that the structural system was effective in redistributing tensile forces as cracking developed. These experimental results give insight into the flexural behavior of precast tunnel segments, providing reliable grounds for calibrating numerical models intended to predict performance both at service-level and under extreme load conditions. 5. Conclusions In this study, an experimental investigation was conducted to evaluate the flexural behavior of full-scale precast tunnel lining segments reinforced with a hybrid RC–SFRC system. Four-point bending tests were carried out on two segments extracted from different positions of a seven-segment tunnel ring, enabling the assessment of their response under pure bending conditions, even if the research does not study the repeatability of the phenomena and needs further tests to capture the statistical variations that may arise for different samples. The experimental results showed that both specimens exhibited a distinct linear-elastic phase followed by a post cracking regime characterized by progressive stiffness degradation. Crack initiation was observed at the intrados within the constant-moment region, after which stable crack propagation, large deformation capacity, and effective tensile force transfer were recorded, indicating a ductile flexural response associated with the reinforcement system.