Size Effect Analysis on Shear Mechanical Behavior of Prestressed RAC Beams Under Dynamic Loading

To reveal the evolution laws of shear mechanical behavior and size effect of prestressed Recycled Aggregate Concrete (RAC) beams under dynamic loading conditions, a three-dimensional five-phase meso-scale numerical model was established based on the ABAQUS2020 software. The bond–slip behavior between steel bars and concrete was considered, and prestress was applied using the temperature cooling method. The effects of prestress level, cross-sectional size and strain rate on failure modes, load–displacement curves, ultimate shear capacity and nominal shear strength were systematically investigated. The results show that increasing the prestress level can significantly restrain the initiation and propagation of diagonal cracks, reduce the brittleness of the failure mode, and effectively mitigate the shear size effect. The nominal shear strength decreases obviously with an increase in cross-sectional size but increases significantly with an increase in strain rate, exhibiting a pronounced strain rate hardening characteristic. Large-scale beams are more sensitive to strain rate, and a high strain rate can reduce the disparity in shear performance among members of different sizes and further weaken the size effect. Based on Bažant’s Size Effect Law (SEL), a modified formula for dynamic shear strength considering the coupled effects of prestress level, strain rate and cross-sectional size was proposed by introducing a prestress enhancement coefficient γ and a strain rate enhancement coefficient β. The calculated results of this formula are in good agreement with the numerical results obtained in this study. Within the investigated parameter range, the present work can provide a reference for the shear design and safety assessment of prestressed recycled aggregate concrete beams under dynamic loading.