Conference Agenda

Numerical modeling plays a key role in assessing the safety and performance of reinforced con-crete nuclear containment buildings (NCBs). However, uncertainties arising from material heterogeneity, boundary imperfections and modeling assumptions can significantly affect predictive accuracy. This paper pre-sents a Bayesian updating (BU) framework for reducing such uncertainties in finite element simulations. The methodology employs a Markov-Chain Monte-Carlo (MCMC) algorithm to infer posterior parameters distri-butions based on experimental evidence. Its implementation is first illustrated through a simply supported beam under a central load, highlighting the influence of the algorithmic settings (number of chains, sample size, proposal scale, and measurement noise) on posterior convergence and uncertainty reduction. The framework is then applied to the PACE-1450 mock-up, a reinforced concrete representative structural volume of NCBs, using a surrogate model to assimilate observed crack counts. Results show significant variance reduction for key parameters, an improved agreement with experimental data and an enhanced predictive capability of damage-based numerical models.

With the publication of the second generation of EN1992-1-1, many changes are introduced in the shear design of concrete elements. Among those, the implementation of prestress in the shear resistance in the cracked regions of prestressed elements without transverse reinforcement has changed, since this is now calculated according to the Critical Shear Crack Theory. To verify the new design proposals, a series of prestressed beams are tested, complemented by a virtual simulation of the experiments. In this work, the shear resistance of one prestressed beam is simulated numerically and compared with the experimental outcome. The beam is modelled using the Lattice Discrete Particle Model, an advanced
non-linear discrete element method that explicitly models the aggregates and the cement-mortar matrix.
This makes it particularly well-suited for applications where the material heterogeneity and cracking
behaviour play a dominant role, such as in shear failure. Because of the heterogeneous modelling, the model is a mesoscale model and needs thorough calibration. To this extent, experimental characterisation tests are carried out to quantify the key mechanical properties of the concrete. These properties include the bending and splitting tensile strength, compressive strength, Young’s modulus and fracture energy. These characterisation tests are also simulated virtually to perform the calibration of the mesoscale parameters. Finally, a large-scale beam test is modelled and the load-displacement diagram is compared with the virtually obtained diagram. Together with the global behaviour, the local cracking behaviour is compared by experimental measurements and the final numerical and experimental cracking pattern is compared. Additionally, the obtained shear resistance is compared with the analytically obtained resistance predicted by the CSCT. These results contribute to the validation of the design provisions of Eurocode 2 and showcase the ability of LDPM to simulate experimental outcomes.

Optimization of structural elements in reinforced concrete design is central to modern engineering efforts to reduce self-weight while maintaining or improving strength and ductility, especially in seismic-prone regions. This study presents a comprehensive confinement analysis of Hollow Circular Concrete Sections (HCS) as compared to their Solid Circular Section (SCS) counterparts. Employing a computationally efficient, non-linear finite-layer framework, it develops a numerical procedure that evaluates confined strength using incremental–iterative moment-of-area computations based on a secant-stiffness formulation embedded in a custom finite-layer model.

The study systematically investigates various HCS geometries with different inner-to-outer diameter ratios, longitudinal and lateral reinforcement arrangements, and concrete strengths ranging from 3.4 to 5.4 ksi. The confinement effects are analyzed using a modified Mander-type concrete model adapted for hollow geometries, with attention to stress distribution across the annular cross-section. Axial–moment interaction diagrams are produced for a wide range of experimental configurations, allowing direct performance comparison.

Results show that, with proper detailing, HCS can achieve confinement performance comparable to that of equivalent SCS, particularly when tri-axial reinforcement is used. Overall, the study demonstrates the potential of hollow concrete columns as a sustainable and high-performance alternative to traditional solid members, paving the way for advanced structural typologies in both high-rise and infrastructure applications.

Concrete cover spalling caused by reinforcement action is characterised by a pressure acting on the internal surface. The plasticity theory exhibits limitations when used for predicting the mechanical response during crack propagation since concrete exhibits tensile softening, which may be taken into account by implementation of so-called effectiveness factors. Therefore, this contribution proposes an analytical methodology with the goal of predicting post-peak softening until the concrete cover spalls. A continuum Finite Element model is used to analyse crack propagation, the kinematics of the system and the propagation of the principal tensile stress along the relevant cracks. Subsequently, an analytical model is developed, where cracks are explicitly considered following Baˇzant’s crack band theory, which propagate towards the surface. Stresses, strains and crack widths are defined according to the deformed state of the spalling concrete body. By expressing that the system should be in static equilibrium for all deformed states, the internally applied pressure is expressed as a function of the deformed state. Eventually, the pressure - displacement diagram is plotted and compared with experimental results from the literature. It is shown that the peak pressure can be reasonably well predicted and that it is possible to capture post-peak softening by applying simple methodologies. Further improvements are possible to be explored in future work.

Numerical modeling of reinforced concrete (RC) elements is well established, but hybrid rebar–
fiber-reinforced concrete (RFRC) systems introduce additional challenges due to high nonlinearity from complex material behavior and fiber-rebar interaction. With Eurocode 2 (2027) incorporating fiber-reinforced concrete provisions, reliable constitutive models are essential. This study evaluates modeling strategies for RFRC beams in Abaqus using the Concrete Damaged Plasticity model. Two post-cracking tensile laws are examined: the Eurocode 2 Annex L formulation and an inverse-analysis model derived from notched beam tests. Rebar–concrete interaction is modeled using both embedded constraints and cohesive zone approaches. Moel validation is performed against four-point bending tests from an ongoing program on minimally reinforced beams with three polypropylene fiber volume fractions. Results show that the Annex L model provides reasonable predictions for polypropylene fibers. Both interaction approaches capture global structural behavior with respective advantages in computational efficiency and deformation accuracy, although the final failure response remains mesh-sensitive when strain-based material criteria are used.