Conference Agenda

While state-of-the-art constitutive models are able to reproduce the mechanical behavior of concrete under compressive and tensile loading with satisfactory accuracy, more complex failure modes caused by shear or mixed-mode loading often result in inaccurate predictions in numerical simulations. Although numerous constitutive models have been developed in recent decades, the systematic validation and objective performance assessment of such models have received comparatively little attention. The present contribution assesses the predictive capabilities of state-of-the-art constitutive models under shear-dominated and mixed-mode failure. A gradient-enhanced extension of the Microplane M7 model, originally proposed by Caner and Bazant (2013), is compared to two established approaches: a gradient-enhanced extension of the Concrete Damage-Plasticity model by Grassl & Jirasek (2006) and the gradient-enhanced Microplane Damage-Plasticity model by Zreid & Kaliske (2018). The predictive accuracy of these models is assessed using three-dimensional implicit finite element simulations of benchmark tests involving notched prismatic specimens subjected to torsional, antisymmetric four-point, and combined shear-tensile loading. Special focus is placed on the models’ ability to predict the load-bearing capacity and post-peak behavior, including crack initiation and propagation. The results show that two of the three investigated models provide accurate predictions of shear-dominated concrete failure, while the third exhibits limitations under such loading conditions, indicating that further refinement remains necessary.

This study presents a series of non-linear finite element analyses (NLFEA) conducted in conjunction with an experimental campaign on prestressed concrete beams made continuous by a cast-in-situ diaphragm and deck slab. Due to the lack of experimental data for this beam typology and its intricate structural
behavior, these specimens provide an ideal test-case for an unbiased numerical study. The analyses include blind predictions, post-dictions, and sensitivity studies on six specimens. Sensitivities are explored by varying finite element discretization, constitutive models, and solution procedures. A brief overview of the experimental program is provided, and a reference model is established as the basis for the numerical study. NLFEA results are compared with experimental findings, and model uncertainties are quantified. Blind prediction outcomes demonstrate that the reference model can accurately estimate ultimate failure load and failure mode, where the post-dictions result react rather insensitive to updated material properties. However, the numerical response is significantly influenced by element size and the adopted smeared crack formulation (rotating versus fixed crack approach). It remains unclear whether this size dependence arises from specific modeling choices or structural details unique to the experiment. Further investigation into this topic is needed and is part of ongoing research activities.

In the present study, a mathematical framework for modeling the behavior of concrete under large deformations is developed. To capture the full degradation process of concrete, an over-nonlocal damage-plasticity theory based on an implicit gradient formulation is employed. Specifically, the coupling between plasticity and damage enables the description of both irreversible deformations and the softening characteristic of concrete, while the nonlocal formulation eliminates localization and mesh dependency, ensuring a realistic prediction of the material response. In addition, a finite element formulation is derived, incorporating the equilibrium equations along with an additional field associated with the Helmholtz-type equation of the gradient-enhanced model. The evolution equations are numerically integrated using a strongly objective algorithm, and the stress-update procedure is presented. Finally, the predictive capabilities of the proposed framework are demonstrated through simulations of reinforced concrete specimens, focusing on the loss of stability and failure of reinforced columns under compressive loading.

This study presents a 2-D numerical framework to simulate the behavior of reinforced concrete
(RC) beams, both unstrengthened and externally strengthened with fiber-reinforced polymer (FRP). The approach is based on an alternative Finite Element Method (FEM) that uses positions instead of displacements as primary unknowns, allowing for a natural treatment of geometric nonlinearity. The Mesh Fragmentation Technique (MFT) is adopted to capture the nonlinear behavior of concrete by inserting High Aspect Ratio (HAR) solid elements between bulk elements. Crack initiation and propagation are modeled through a continuous damage model applied only to the HAR elements, keeping the bulk elements linear elastic. A position-based HAR interface element is also introduced to model the interaction between concrete and reinforcements. A J2 continuous damage model describes the bond-slip behavior and degradation between concrete, steel bars, and external FRP sheets or plates. The main contributions include the integration of the MFT with HAR interface elements to represent both crack growth and bond deterioration, combined with the extension of these concepts to a position-based FEM for general nonlinear analyses. The results confirm that the proposed framework accurately reproduces the response of RC beams and captures FRP debonding due to intermediate crack formation.

Unreinforced masonry (URM) walls are highly sensitive to non-proportional loading histories, particularly when foundation settlement precedes lateral loading. In such cases, pre-damage induced by settlement can significantly affect the subsequent structural response and cannot be adequately represented using
proportional loading assumptions or equivalent reduction factors. A Total Sequentially Linear Analysis (Total SLA) framework is developed to investigate the combined effects of boundary conditions, geometry, and settlement-induced pre-damage on the pushover response of URM walls. The numerical model represents masonry units as linear elastic continua and concentrates nonlinearity within zero-thickness interface elements governed by discrete damage modes. Settlement and pushover are applied sequentially within a unified event-driven formulation, allowing damage states to be inherited across loading stages. The results show that the initial elastic response is largely insensitive to the top boundary conditions, whereas significant differences emerge during the softening phase. Fixed-top configurations exhibit a more gradual degradation of stiffness. Cantilever and free-top conditions, in contrast, show sliding-dominated behavior. Settlement causes irreversible damage, reducing both stiffness and peak capacity during subsequent pushover loading. The effects are amplified in walls with openings. These results demonstrate that neglecting load-path dependency may lead to inaccurate predictions of stiffness degradation and peak capacity in URM walls.