Conference Agenda

This paper presents development of a 3D nonlinear FE model of a concrete biological shield (CBS) in a nuclear power plant using WWER 440/213 nuclear reactor. Such structure is exposed to several nonmechanical effects, primarily the neutron radiation causing the radia-tion-induces volumetric expansion (RIVE). This causes internal stresses within the structure and years of op-eration lead to cumulation of this effect, finally developing into cracks. Crack propagation then disrupts the structure's soundness and may lead to reduced shielding property. RIVE is introduced to the analysis as an isometric eigenstrain, varying along the height, depth and in circumference along the inner surface. The results focus on determining crack initiation and propagation. The primary vertical crack appears after approx. 6 years of operation and reaches width of 0.3 mm after approx. 12 years. After considered lifespan of 60 years, the primary crack reaches width of 4.6 mm.

For retrofitting purposes, there is a demand to reinstate or increase the capacity of damaged or non-damaged columns. In addition to confinement techniques, section extensions to columns are often employed. Adhesion and mechanical anchoring over the interface are required to achieve the column's full capacity. During the hardening process of the concrete, shrinkage of the newly cast extensions results in supplementary loading of the existing part of the column. The present work, based on the principles of composite action, considers one-directional enlargements, focusing on the normal forces in the column components and the shear flow acting on the interface. Additionally, fire action on an existing column that is enlarged on two opposite sides, is considered. It is demonstrated that optimizing bar locations in the new parts leads to a significant increase in fire safety.

This paper investigates the vulnerability of reinforced concrete (RC) frame structures under extreme loading conditions such as blast and high-velocity impact events, emphasizing complex responses and secondary failure mechanisms. Explosions in close proximity generate intense shock waves that damage vertical load-bearing elements, particularly columns, leading to loss of load path continuity and potential progressive collapse. The study focuses on catenary mechanisms that temporarily redistribute loads but induce excessive tensile forces, accelerating failure. Traditional design approaches based on predefined threat scenarios are critically compared with more general, threat-independent frameworks such as dynamic column removal, which promote robustness through redundancy and alternative load paths. While threat-dependent methods provide accuracy for specific cases, they may overlook unforeseen failure modes, whereas threat-independent approaches aim to ensure resilience against a wider range of hazards. A numerical case study of a short RC frame using the Applied Element Method quantifies structural response under different damage scenarios, including sudden column loss and blast loading. The comparison of results highlights differences between threat-dependent and threat-independent frameworks, emphasizing the role of initial damage characteristics and secondary mechanisms in collapse progression. The findings underline the need for robustness-oriented design methodologies that address uncertainties in loading scenarios and enhance the capacity of RC frames to resist and adapt to extreme events while preventing progressive collapse.

Rockfall protection systems are essential for safeguarding infrastructure and human activities in mountainous regions, where falling rock masses pose persistent hazards that can cause severe damages. Structural mitigation measures, such as energy-dissipating barriers, are commonly installed near roads, buildings, and industrial facilities to reduce impact forces. These systems function by either absorbing the kinetic energy of falling blocks through deformation or resisting impact via mass and frictional dissipation. Two main energy dissipation strategies characterize these systems. Flexible barriers, such as net fences, absorb energy through large deformations and are widely used for their adaptability and effectiveness across varying block sizes. However, they require sufficient clearance between the barrier and protected infrastructure, which limits their application in narrow corridors. To overcome this constraint, rigid systems, such as L-shaped reinforced concrete walls, have been developed. For high-impact energies, a cushion layer of granular material is often added to the upslope face of the wall. However, this solution requires a large footprint, which is not always feasible, and in steep areas, the added weight can even lead to overall slope instability. Therefore, for expected impact energies up to approximately 800 kJ, a rigid system alone can represent an effective and economical solution. These structures rely on mass and bending resistance to dissipate energy without requiring buffer space, making them suitable for constrained environments. Nevertheless, their long-term reliability under diverse impact conditions remains an open question. This study introduces a time-integrated reliability analysis of rigid rockfall protection systems, focusing on performance under variable loading over extended periods. The approach incorporates the frequency–magnitude distribution of rockfall events, acknowledging that smaller blocks occur more frequently than larger ones. Variability in block mass, impact velocity, and kinetic energy is modelled within a probabilistic framework that accounts for uncertainties in material properties and structural response. The analysis is applied to a real-world slope with documented rockfall activity, evaluating the reliability of a concrete wall system under cumulative low-energy impacts and rare high-energy events. Using limit state functions, failure probabilities and critical performance thresholds are estimated. Results emphasize the importance of integrating temporal and probabilistic dimensions into design, showing that rigid barriers, while effective in constrained spaces, exhibit reliability sensitivity to impact frequency, energy dissipation capacity, and degradation over time.

The connection between flat reinforced concrete slabs and columns represents a critical design challenge in structural engineering, particularly in buildings, due to the substantial concentration of shear stresses that can lead to punching failure. This localized, brittle failure mechanism occurs abruptly, without prior warning, and carries a considerable risk of structural collapse. Despite extensive research aimed at understanding the mechanics governing punching shear failure and developing dependable design methodologies, such as the Critical Shear Crack Theory (CSCT), a unified understanding of the underlying phenomena remains elusive. This investigation makes use of the Finite Element Method (FEM) in conjunction with material models based on fracture mechanics to simulate punching shear failure in reinforced concrete slabs. While this methodology has been previously explored, challenges persist, particularly in accurately representing the overall response of the problem and the failure mechanisms involved. The objective of this work is to evaluate various modelling approaches to establish a numerical model capable of accurately reproducing this phenomenon, thereby offering insights into the intricate fracture mechanisms that drive the failure process. The numerical simulations draw upon experimental data from Kinnunen and Nylander’s seminal work, specifically referencing specimens IA15a, IB15a and IC15a. These slabs are circular, with a diameter of 1840 mm, are supported by a 150 mm diameter column, with both the column height and slab thickness being 150 mm, and incorporate different reinforcement strategies. While IA15a slab presents an orthogonal reinforcement, IB15a is reinforced with ring reinforcement and IC15a with a combination of ring and radial reinforcement. The experimental setup involves applying load from below the specimen using a hydraulic jack, while the slab’s perimeter is constrained vertically by twelve spreader beams. The FEM models employ an isotropic damage formulation to describe concrete behaviour, where damage reduces the material’s stiffness and is determined using an equivalent strain value based on the Rankine criterion. Steel is represented by a perfectly plastic material, adhering to the von Mises plasticity condition. A key focus of this study is the examination of the concrete-steel interface behaviour. Two distinct model versions are prepared for each of the three slabs: one of them assume perfect bonding between steel and concrete and do not allow debonding, while the other one permits perfect slippage between concrete and steel. The numerical findings underscore the critical importance of accurately modelling the concrete-steel interface. Notable differences in the load-displacement diagrams between those models where slippage is not allowed and those where it is allowed, emphasize the significant influence of bond-slip behaviour in accurately capturing the punching shear response of reinforced concrete slabs. This research contributes to a deeper understanding of punching shear failure and supports the development of more reliable numerical tools for structural design.