Experimental and meso-scale investigation of size effect on fracture properties in three-point concrete beams (TPB)

In this study, the size effect on concrete fracture parameters has been investigated in three distinct groups. While the geometry is similar across each group, the span-to-height ratio varies among the three groups. The study investigates the impact of three different span-to-height ratios (1.85, 2.65, and 4) and five different notch-to-beam height ratios (0.1, 0.2, 0.3, 0.4, and 0.5) by using three-point notched beams (TPB). Beams with iden-tical spans but different heights are used. A new method is proposed to determine the fracture properties of concrete based on the Boundary Effect Method (BEM). A proposed formula for the fictitious cracks is presented based on the results of numerical analyses at the mesoscale and used in the BEM to determine the values of tensile strength and fracture toughness with the effects of span-to-height ratio. The established mesoscale frac-ture model reproduces the load-displacement curves of 3 PB specimens concrete, which verifies the rationality of the model with the experimental results. Numerical simulation reveals that the fictitious crack length in concrete is highly sensitive to the size of aggregates, their distribution and spacemen's dimensions. Discussion on BEM based on principles of mathematical fitting and data processing is provided for more objective quasi-brittle fracture experiments and modeling. The size effect law (SEL) is limited by its requirement for sample geome-tries to be similar, which introduces some additional error when applied to samples with dissimilar geometries. To minimize this error, this study proposes a new formulation within the BEM method. It is found that the fracture parameters predicted by the BEM method using the proposed formulation for different geometries are consistent with the size effect law (SEL) for similar geometries.