Due to difficulties in performing fluid-solid coupled crack propagation experiments of concrete, simulations can provide significant insight into complex behaviors of concrete and structures. However, the simulation of concrete responses with microstructural features under fluid-solid coupled crack propagation is still a challenging task. In this study, a poromechanics based phase-field fracture model was implemented. The flow through concrete and crack was assumed to be laminar, where Darcy and Poiseuille flows were adopted for the concrete matrix and cracks, respectively. The modeling parameters were calibrated to wedge splitting test experiments subjected to fluid pressure. The calibrated model was then applied to simulate the responses of concrete specimens with twophase microstructures consisting of mortar and large aggregates. The reduction in strength due to fluid pressure was identified, and the effect of aggregates on the mechanical responses of concrete was analyzed. It is confirmed that the implementation of the poromechanics based phase-field fracture model can be successfully used to investigate the fluid-solid coupled mechanical behaviors of
concrete considering complex microstructures of aggregates.

Rapidly changing climatic conditions confront communities in alpine regions with great challenges and necessitate the continued development and optimization of geohazard mitigation solutions. One such solution is presented by flexible rockfall barriers, which constitute a frequently employed system for mitigating the risk posed by rockfall. Despite their widespread use, the design of their foundations is characterized by great uncertainty. Moreover, the construction of such foundations requires heavy machinery and constitutes a major part of the cost of the completed barrier. To optimize the design of rockfall barrier foundations, a better understanding of their mechanical behavior is needed. To this end, a three-dimensional finite element model of a rockfall barrier foundation subjected to impact is developed and implicit dynamic mechanical simulations are carried out. Results indicate that the developed finite element model is capable of predicting the forces acting on the foundation and its components during an impact event. A detailed investigation of the interaction of the individual components reveals that damage to the foundation’s concrete plinth is accurately captured by the model if an over-nonlocal gradient-enhanced constitutive model for concrete is employed. Moreover, the contact between the concrete plinth and the surrounding soil is identified as a key parameter influencing the mechanical behavior of the concrete plinth during impact. This work highlights key factors influencing the mechanical behavior of rockfall barrier foundations during impact and directly complements recent full-scale impact testing of such foundations performed at the University of Innsbruck.

In this contribution, a time homogenization (TH) scheme is utilized to accelerate the computational simulation of fatigue induced crack propagation in engineering materials, specifically focusing on concrete subjected to cyclic loads. The proposed approach segregates the problem into distinct micro- and macro-time scales, improving computational efficiency by extrapolating internal variables linked to material fatigue. This method, originally applied to multi-scale problems such as tire life cycle analysis, is now adapted to model fatigue induced damage in concrete structures. The model is built on a modified phase-field formulation that considers material degradation due to fatigue and the Representative Crack Element formulation as an energy split. The time homogenization accelerates the simulation by upscaling micro-scale behavior over extended macro-time periods. The model performance has been previously tested against high-fidelity simulations and it has been demonstrated the method’s potential to effectively model crack growth under various loading conditions. The novelty of this approach lies in its application of a methodology based on computational homogenization to fracture mechanics. By utilizing this framework, the computational burden is significantly reduced, providing results that approximate high-fidelity simulations with much shorter processing times. In this contribution, the time homogenization scheme is extended to experimental validation, utilizing data from fatigue tests. A comparison between simulation results and experimental observations is presented, demonstrating the method’s accuracy in replicating crack growth patterns and fatigue behavior. The results confirm that the time homogenization approach offers a reliable and efficient alternative to traditional methods, particularly in high-cycle fatigue cases, reducing computational time without sacrificing accuracy.

BubbleDeck type slab (BD) is a lightweight construction system for building floors where recycled plastic hollow spheres (RPHS) are disposed in its core to decrease its deadweight without significant loss of stiffness, flexural and shear strength. However, the behaviour of BD under punching loading conditions is not yet well known, despite its use in real practice has increased significantly in the last years. Since punching is a brittle failure mode, in this work an experimental program with BD prototypes is complemented with advanced numerical simulations to assess not only the punching capacity of BD but also to explore the potential of nonlinear finite element analysis on the simulation of this complex structural system. When compared to the equivalent solid RC slabs (SS), the experimental tests showed a smaller performance in terms of punching capacity and ductility. Regarding the numerical simulations, a multidirectional fixed smeared crack model applied to a refined finite element mesh where concrete was simulated by solid finite elements, and steel reinforcements were considered perfectly bonded, was demonstrated capable of capturing the main experimental records, namely the load vs deflection and strains in the constituent materials. This demonstrates that this numerical approach can be explored to optimize numerically the BD to have larger punching capacity and ductility, such is the case of using fibre reinforced concrete.

Understanding the degree of reinforcing bar corrosion in reinforced concrete (RC) structures is crucial for evaluating the behavior. This study develops a simulation system for estimating the corrosion distribution along the rebar of a RC beam member based on surface crack widths. The system integrates the rigid body spring model (RBSM) with machine learning methods. The RC beam is modeled and RBSM simulations with different expansion distributions are run with 500 analysis steps. The expansion data and the corresponding surface crack width data generated from the simulations are used to build the training dataset for machine learning. A large number of training data samples are obtained by extracting the simulation results step-by-step. The inputs are surface crack widths from several locations and the desired output is the internal corrosion-induced expansion. After training with the dataset, the neural network is able to correlate inputs and outputs, allowing it to estimate an expansion distribution from given cracking data. The estimated expansion distribution is then used to simulate the surface cracks using RBSM, and the error between the given cracking data and simulated cracks is returned as an input to the trained network in order to optimize the expansion estimation and enhance performance of the system. The feasibility of the proposed RBSM-neural network system is validated using both synthetic and experimental test data. The estimation results align well with the target data, demonstrating the effectiveness of the system in estimating internal expansion along the rebar and reproducing the cracking distribution using surface crack data. Internal distributions of cracking and stress states are extracted from the simulations, providing additional information for further analysis of structural performance.

Concrete interfaces between aggregates and cement paste are critical zones for crack initiation and propagation. At nanoscale, the interface between Calcium Silicate Hydrate (CSH) and silica is crucial as its cracking significantly affects the structural performance. In this study, classical Molecular Dynamics (MD) simulations are employed to examine the crack growth mechanisms in notched specimens under Mode-I loading. The effect of notch size and its orientation on the fracture behaviour of CSH-silica interface is explored through reactive MD. The interface is characterized by atomic-level interactions, stress distribution, and energy dissipation, providing substantial insights into the fracture toughness and crack propagation. The study highlights the key aspects of atomic debonding, crack initiation and growth. Thus, contributing to a deeper understanding of the mechanical integrity and fracture resistance of cementitious materials. The results reveal that the larger notch size and unfavourable orientations lead to accelerated crack propagation and reduced fracture resistance. While smaller or optimally oriented notches enhance the specimen’s ability to withstand the applied stresses. These findings contribute to a better understanding of fracture mechanics in concrete at the nanoscale and offer valuable guidance for optimizing concrete design for improved durability and performance.