High-Performance Steel Fibre Reinforced Concrete (HPFRC) Flexural Fatigue Design with Upgraded $$S-N$$ Curves

Civil structures and strategic infrastructures are frequently subject to deterioration due to cyclic actions throughout their service life, which can jeopardise their structural stability even at low stress levels. A remarkable enhancement in the fatigue performance of concrete structures can be achieved thanks to the introduction of fibres, since they provide higher toughness to structural elements, with specific regards to the mechanical response at stress levels exceeding the cracking and damage thresholds in compression and bending. The synergy between a highperformance concrete matrix and fibre reinforcement can be particularly conducive to the improvement of fatigue performance. One of the most promising fields for the application of the resulting High-Performance Fibre Reinforced Concrete (HPFRC) materials is represented by structures and infrastructures - including bridges, pavements, infrastructures for energy harvesting - whose service condition is governed by cyclic loading throughout their service life. The characterisation of the fatigue behaviour of the materials hence represents a crucial aspect for structural design of the aforesaid engineering artefacts. To this aim, in the present study, a HPFRC mix has been tested under compression and bending fatigue loadings at different stress levels and number of cycles. With reference to flexural tests, fatigue resistance has been then compared with the estimation of fib Model Code, which proposes, for constant stress amplitudes, numerical correlations - the S − N curves - to evaluate the number of cycles to failure based on the type of actions and the stress levels. These correlations, however, are based on empirical experience on plain concrete and adjustments are required for a proper implementation in the fatigue design of new cementitious materials. The present work provides a tailored S−N curve formulation by calibrating the existing coefficients based on the experimental characterisation conducted on a performance-based HPFRC mix design.