Concrete fatigue propagation from material to structure: Multiscale validation of a thermodynamically based discrete model on prisms and prestressed beams

Fatigue assessment of concrete structures relies predominantly on empirical evidence from uniaxial cylinder tests, codified into structural design rules. Several continuum damage-plasticity models have been developed to capture fatigue-induced dissipative mechanisms. However, they do not explicitly resolve how damage propagates through the aggregate skeleton and translates into structural behavior. This study addresses this gap by integrating a thermodynamically based inter-aggregate constitutive law into a lattice discrete particle model that explicitly represents mesoscale concrete heterogeneity. The thermodynamic formulation inherently decomposes dissipated energy into contributions from distinct degradation mechanisms, enabling mechanism-specific fatigue characterization. The model is calibrated using macroscopic characteristics of monotonic and fatigue response of prisms under compression and validated against prestressed beam experiments under variable-amplitude fatigue loading. Simulations reproduce experimental trends of fatigue response in prestressed beams, revealing two key findings: (i) the obtained Sparks-Menzies relation persists across material and structural scales; (ii) damage dissipation emerges as a scale-consistent, load-level-independent indicator of fatigue capacity within a given stress configuration, offering a physically grounded alternative to empirical design criteria. The present high-fidelity model provides the basis for resolving the transition from meso-scale material behavior to macroscopic structural response, and establishes a foundation for future coarse-graining and time-scale acceleration strategies required for large structures and long fatigue lives.