In this paper, the performance of smeared crack and discrete crack dilatancy models applied to mixed mode fracture is evaluated. Fixed, rotating as well as hybrid rotating-to-fixed smeared crack models are considered. For each crack model format-specific input parameters such as the shear retention factor, the reduction of compressive strength due to lateral cracking, and the transition point from rotating to fixed are varied respectively. Elementary tension-shear model problems are considered including validation against recent mixed-mode lab tests. The results indicate that the fixed crack response is highly sensitive to the choice of shear retention factor, while the rotating crack results are sensitive to the adopted boundary conditions of the model problem. The hybrid crack formulation does not provide consistent advantages compared to the fixed or rotating crack formulations. The discrete crack dilatancy models are found to be more accurate in predicting the mixed mode response of the tests, although they tend to overestimate the shear strength. Reference is made to early work by Willam.

Two-dimensional (2D) mesoscopic simulations of accelerated corrosion tests are frequently performed to avoid the much higher computational costs of three-dimensional (3D) mesoscopic simulations. 2D models assume geometric invariance of the mesostructure in the direction perpendicular to the analyzed plane. However, this is different from the real concrete mesostructure, consisting of polyhedral (rather than cylindrical) aggregate particles embedded in a mortar matrix. This provides the motivation for a comparative analysis of 2D and 3D mesoscopic simulations of the accelerated rebar corrosion test by Andrade et al. [Mat. Struct., 1993, 453-464]. The 3D model resolves the concrete mesostructure in the vicinity of the rebar into polyhedral aggregates, embedded in the mortar matrix. The 3D simulation accounts for non-uniform corrosion penetration into the rebar, non-uniform rust deposition on the rebar surface, and crack propagation through the mesostructure of concrete. Four 2D models are generated from four different cross-sections through the 3D model, perpendicular to the axis of the rebar. The 2D simulations are based on the assumption of either a plane strain state or a plane stress state. The comparison of the results of 2D and 3D simulations indicates that the 2D simplification does not necessarily result in the realistic simulation of the interaction of propagating cracks with the aggregates. This may lead to wrong predictions of crack propagation paths and crack opening widths.

Ultra-high performance fibre reinforced concrete (UHPFRC) emerged in the last two decades as a technologically sound building material. It is well known that, in direct tension, softening takes place for an UHPFRC as long as its fibre content is relatively small. However, strong hardening may still be obtained for such a material in bending with, possibly, concurrent stable, multiple cracking. Yet, the ability to harden under bending is not a material property, but a mixed material-structural property, and thus subjected, very particularly, to size-effect, where the expression size-effect is used in this context in its widest sense of the influence of size on all the aspects characterizing the mechanical response, such as the full load-displacement curve and the whole evolution of the crack pattern. In this paper, some basic results of a wider numerical study of size- and material-effect are reported for softening UHPFRCs characterized by a steep initial softening due to matrix cracking followed by a long, slow softening due to fibre-bridging. The simulations were devised to investigate the coupled influence of the initial softening slope and of the fibre bridging stresses on the response of similar beams in pure bending, and cracking was simulated using finite elements with embedded cohesive cracks (in Hillerborg’s sense). The results show that the nominal stress at visible crack initiation depends essentially on the sharp initial softening and specimen size, while the intensity of post-crack hardening and mean crack spacing (as well as mean crack opening) depend on the fibre bridging strength and the specimen size. Dimensionless plots are provided that allow utilization of the results for other combinations of data in the domain of the simulations.

This research investigates the behavior of concrete tubular segmental beams prestressed with PC bars, focusing on the load-deflection characteristics and failure mechanisms. The interface parameter obtained from experimental results provides insight into modeling the epoxy joints used in large wind turbine towers. Specimen S8-JI2 exhibited failure patterns, load-deflection behavior, and tensile stress comparable to those observed in the experimental specimen. A unique failure mode dominated by longitudinal cracks was observed, explained by the arch mechanism activated when the interface joint opened. This led to a shift in the neutral axis, resulting in compressive stress transfer within the UFC and generating lateral stresses, which caused horizontal cracks. The study also found that reducing steel fiber content from 2% to 1.2% resulted in reduced load-carrying capacity and altered failure patterns, with the arch mechanism becoming more prominent in the lower fiber content specimen. Additionally, normal concrete specimens exhibited pronounced diagonal cracking due to interface opening, particularly in the central segment of the beam.

The crack evolution in concrete under drying conditions is significantly influenced by the shape of aggregates. This study presents a fully coupled three-dimensional hydro-mechanical peridynamic (PD) meso-scale model for partially saturated porous media to simulate crack formation in cementitious materials during drying shrinkage. Simulations were conducted on concrete samples with different aggregate shapes, including regular polyhedron (e.g., hexahedron, octahedron, dodecahedron, and icosahedron) and spheres. Results indicated that aggregates with lower sphericity led to higher stress concentrations and an increased formation of fine internal cracks. In contrast, aggregates with higher sphericity, such as spheres, produced a more uniform damage distribution, with fewer surface cracks. Damage analysis demonstrated that the sphericity of aggregates influenced early surface damage and denser crack networks, while higher sphericity in aggregates reduced the overall volume of internal cracks. The evolution of internal cracks over time underscored the sensitivity of the concrete matrix’s mechanical response to aggregate morphology. This fully coupled hydro-mechanical PD model enhances our understanding of fracture behavior in concrete under drying conditions and underscores the critical role of aggregate shape in crack development. The insights gained from this study support optimized aggregate selection and improved structural design strategies to minimize drying shrinkage damage, contributing to the durability of concrete structures.