Constitutive model for ultra-high performance concrete (UHPC) considering the size effect under cyclic compressive loading

In this study, the size effect of the thickness of the specimen on the mechanical properties of UHPC was investigated through compression tests under cyclic loading. UHPC prisms with different thicknesses from 20 mm to 100 mm were tested under unloading/reloading cycles and the stress-strain curves were recorded for this purpose. A constitutive model to predict the stress-strain response of UHPC accounting for the thickness was proposed. It was found that UHPC specimens with different thicknesses showed the same failure mode of di-agonal shear failure. The size effect of thickness was significant for the compressive strength but was negligible for the peak strain and elastic modulus. The damage of the unloading modulus and reloading modulus at zero stress only occurred when the unloading strain exceeded 0.8 times the peak strain. Furthermore, the proposed constitutive model could predict the stress-strain response for UHPC with different thicknesses under cyclic compressive loading with acceptable accuracy.