Conference Agenda

In this contribution we discuss the differences and similarities of two extensions of damageplasticity approaches for concrete: (localizing) gradient-enhancement and the phase-field approach to fracture. Due to the similarities of their governing equations, we first present a general framework encompassing both approaches. In a second step we elaborate on their numerical implementation, and show that the same type of finite element—characterized by one scalar field, i.e., the phase field or the nonlocal damage driving force, in addition to the displacement field—can be used for both approaches. However, the consistent tangent operators on finite element level differ slightly. The capabilities of the models are assessed by means of two numerical benchmark examples, namely the L-shaped panel test and three-point bending tests on notched specimens. In conclusion, both approaches are promising in terms of their ability to deliver mesh-insensitive solutions, localized crack patterns, and overall structural response. Hence, in the future, a more detailed investigation, including more complex failure mechanisms, is required for an in-depth assessment of the models.

Advances in 3D-printed concrete (3DPC) require numerical models capable of capturing its lay-ered structure and interfacial behavior. This work introduces a novel LDPM-based modelling approach in which the full specimen is discretized with tetrahedra, and interlayer behavior is described by locally modifying the meso-scale properties of elements positioned within the printed interfaces. As a first proof of concept, interlayer facets are assigned reduced mechanical properties, assuming a 30%, 35% and 40% decrease in tensile, shear strengths and fracture energy relative to the bulk material. A parameter-sensitivity study is performed across multiple LDPM realizations to assess how random meso-structural arrangements influence the global response. The simulations exhibit characteristic variability in failure patterns, with crack initiation occurring either along mid-span or along the weakened interlayer depending on the seed. The results demonstrate the capability of this location-based LDPM strategy to capture interlayer-driven variability and lay the groundwork for future cali-bration against experimental data.

This contribution presents a three-dimensional force-based Timoshenko beam formulation for the nonlinear analysis of prestressed concrete members with evolving bond-slip interaction. A set of slip degrees of freedom is introduced at the element level to represent the relative displacement between tendons and concrete, governed by a nonlinear bond law and compatible with arbitrary tendon layouts. Prestressing can be applied through initial strains, imposed slip, or force-controlled loading, and the element naturally accommodates staged activation, grouting, and time-dependent losses due to shrinkage, creep, and relaxation. Tendon strains are obtained by projecting the beam deformation field onto the tendon axis through an isoparametric mapping, enabling the simulation of curved bonded or unbonded tendons. Concrete behavior is modeled through a three-dimensional damage-plasticity law, while tendons and reinforcing steel follow uniaxial nonlinear constitutive models. The resulting element combines force interpolation, explicit slip kinematics, and consistent sectional integration within a computationally efficient force-based framework. A validation study on prestressed CFRP-strengthened beams demonstrates the ability of the model to capture bond degradation, anchorage softening, prestress losses, and rupture-induced force redistribution. The formulation provides an efficient and general tool for simulating prestressed concrete structures with complex tendon configurations, partial bonding, and staged construction effects.

The J-integral is a well-known path integral used to calculate the energy release rate in an elastic, homogeneous medium with a localized crack. In this study, it is extended to a heterogeneous medium, where Young’s modulus varies spatially according to a lognormal random field. It is shown that the mean of the J-integral remains path-independent and accurately represents the mean energy release rate. However, in a random medium, the mean energy release rate differs slightly from the deterministic case based on the average modulus. The coefficient of variation (CoV) of the J-integral, on the other hand, is generally pathdependent. This means that the variability in the energy release rate is influenced by the specific path chosen for the calculation of the J-integral. The CoV of the J-integral matches the CoV of the energy release rate only when the domain enclosed by the contour is smaller than the correlation length of the elastic modulus field. When the contour encloses a larger domain, the J-integral significantly underestimates the variability in energy release rate. This indicates that, for larger domains, a simple path-based approach is inadequate to fully capture the statistical variations introduced by material heterogeneity. To accurately capture the energy release rate statistics for arbitrary contours, an additional term is derived for the J-integral. This new term is a domain integral that accounts for material heterogeneity.
Furthermore, the analysis reveals that the correlation length of the elastic modulus field has minimal impact on the mean energy release rate but strongly influences its variability. Specifically, for a given specimen, the CoV of the energy release rate decreases significantly as the correlation length decreases.

This study investigates the algorithms for mapping the random fields of material properties onto finite element (FE) meshes and examines their consequences for stochastic FE analysis of damage and fracture in quasibrittle materials. A continuum damage constitutive modeling framework is adopted, in which the constitutive law of each finite element is regularized to ensure correct energy dissipation for different mesh sizes. Three mapping methods for random fields are considered: (1) local mapping, where the constitutive property of an element is directly sampled from the random field at a specific point (e.g., element centroid or integration point); (2) local averaging, where the property is obtained by averaging the random field over the element domain; and (3) mechanism-based mapping, where the projection of the random field onto the FE mesh is governed by the prevailing damage mechanism within the element. These methods are implemented in stochastic FE simulations of recent bending beam tests on Dunnville sandstone. Comparison between experimental and simulated results demonstrates the critical role of linking the mapping algorithm to the evolving damage behavior of individual finite elements. The analysis further elucidates the influence of multiple characteristic length scales—including FE mesh size, correlation length, and fracture process zone width—on the choice of mapping method.