A major challenge of infrastructure management is to predict the remaining capacity of degrading structures and safely prolong their lifetime. In reinforced concrete (RC) structures, concrete cracking has a significant effect on durability and stiffness properties. Structural integrity degradation is often assessed by estimating the global stiffness loss through vibration-based structural health monitoring. Yet, this is challenging as the modal characteristics might also be affected by environmental and support conditions. At the same time, the development of models that enable studying the modal characteristics of cracked concrete structures has received little attention so far. This paper proposes a novel, visual inspection-based method to predict the decrease in effective elastic moduli of existing concrete structures from observed longitudinal and transverse cracks which are typical for corrosion and load-induced damage in RC elements. Discrete and smeared finite element models are developed to establish a relation between the geometrical crack properties and the changes in the concrete's smeared dynamic stiffness parameters, as defined within an orthotropic material model. It is found that the crack pattern has a significant influence, with transverse cracks generally reducing the stiffness parameters more than longitudinal cracks. Experimental data support the proposed relations’ ability to tune the parameters of the orthotropic material model based on crack properties from corroded or mechanically loaded RC beams. The proposed relations enhance the assessment of serviceability limit states in RC beams and offer a valuable tool to evaluate dynamic test data obtained from on-site monitoring.

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The acoustic emission (AE) technique allows monitoring damage in (reinforced) concrete in a non-destructive way by means of piezoelectric sensors attached to the material surface. This approach has disadvantages such as a decrease of the sensor coupling over time, high attenuation of AE waves in concrete, and difficulties in terms of sensor placement. Embedded AE sensors, so-called ‘smart aggregates’ (SA), can be a valuable addition or alternative to surface-mounted AE sensors. However, the embedment of sensors brings its own challenges. In this paper, the use of SA is investigated to monitor cracking of fiber reinforced concrete during a three-point bending test, and corrosion and related concrete cracking of reinforced concrete during an accelerated corrosion test. The novelty of the paper is the application of SA for passive AE monitoring during concrete degradation processes with a varying cracking behavior and crack orientation. Special emphasis is put on data filtering and localization of AE sources. The results show that, despite a higher level of wide-band noise for the SA sensors, they are able to detect and localize concrete cracking after dedicated filtering. Furthermore, the potential of SA sensors in early-stage detection of corrosion damage is demonstrated, offering enhanced possibilities for predictive maintenance of concrete structures.

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Historic masonry structures are particularly sensitive to differential soil settlements. These settlements may be caused by deformable soil, shallow or inadequate foundation, structural additions in the building and changes in the underground water table due to the large-scale land use change in urban areas. This paper deals with the numerical modeling of a church nave wall subjected to differential settlement caused by a combination of the above factors. The building in question, the church of Saint Jacob in Leuven, has suffered extensive damage caused by centuries-long settlement. A numerical simulation campaign is carried out in order to reproduce and interpret the cracking damage observed in the building. The numerical analyses are based on material and soil property determination, the monitoring of settlement in the church over an extended period of time and soil-structure interaction. A sensitivity study is carried out, focused on the effect of material parameters on the response in terms of settlement magnitude and crack width and extent. Soil consolidation over time is considered through an analytical approach. The numerical results are compared with the in-situ observed damage and with an analytical damage prediction model.

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Many existing reinforced concrete (RC) structures are suffering from corrosion damage. The development of reliable tools to characterise and localise such damage is essential to assess the structural capacity. The acoustic emission (AE) technique has proven to be promising for this purpose. However, this technique poses challenges to reliably interpret the results and lacks rigourous validation. In this paper, microfocus X-ray computed tomography (micro-CT) is used to validate the use of AE for the localisation and characterisation of chloride-induced corrosion damage. An experimental protocol is designed, where both techniques are applied on small-scale reinforced mortar samples during accelerated corrosion. In addition to the frequently applied localisation of the AE events, a new signal-based clustering algorithm of the AE events is proposed, which allows to distinguish between different damage processes, such as friction due to the emergence of corrosion products and corrosion-induced mortar cracking. The results obtained from the AE localisation and clustering are confirmed by the micro-CT images and are found to be in line with alternative damage characterisation techniques based on AE parameters, that are found in the literature. Finally, it is shown that the combination of clustered AE events and micro-CT for the considered small-scale samples can help to understand the different damage processes induced by corrosion.

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Differential soil settlements can induce structural damage to heritage buildings, causing not only economic but also cultural value losses. In 1963, the Saint Jacob’s church in Leuven was permanently closed to the public because of severe settlement-induced damage caused by insufficient bearing capacity of the foundation. Currently, the church is stabilized using a temporary shoring system. This work aims at implementing a practical modelling approach to predict damage on church nave walls subjected to differential settlements. For that purpose, a finite element model of the Saint Jacob’s church nave was generated and validated through on-site monitoring data including levelling, damage survey and laser scanning. The model takes into account the non-linear behavior of the masonry by means of continuum smeared cracking. The paper introduces two approaches to model the settlement on the structure. One of them consists in the direct application of vertical displacements underneath the structure according to the deformation profile measured on-site. In the second approach, interfaces with different stiffness are placed at the base allowing the structure to deform under its self-weight. In addition, the effect of the settlement profile type in the damage level is analyzed.

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One of the most common obstacles faced by engineers when making numerical models to assess damage in historical masonry lies in defining the most suitable constitutive models when there is shortage of either material characterization or experimental data. This paper presents the implementation of a 2D finite element model (FEM) of a masonry wall by means of two strategies: a discrete cracking meso-model and a continuum smeared cracking macro-model. A sensitivity study is performed to investigate the effect of material properties variation on both modelling strategies, each of which considers the highly non-linear behaviour as well as the brittle cracking of the masonry. The numerical models are validated through the results obtained from an experimental testing campaign which considered a brick masonry wall subjected to cyclic three-point bending. The results of both modelling strategies compared with experimental results are presented, as well as the criteria considered for material characterization and the sensitivity analysis. Results indicate the suitability of both models to reproduce experimentally observed load capacity, failure mechanism and horizontal deformations. However, the meso-model showed higher accuracy in terms of failure mechanism and plastic deformations. The sensitivity analysis indicated that some material parameters, such as fracture energy, cohesion and tensile strength, significantly govern the final cracking. This is an important criterion for adequately choosing the parameters for further models in which crack width is considered, e.g. for settlement-induced cracking analysis.@en

Limited experimental data of mechanical properties of brick masonry are available in the literature, especially for those properties that determine the cracking behaviour, such as tensile strength and fracture energy. Moreover, the cracking behaviour is influenced by several other factors such as the type of components, bond type, size of the element and loading conditions. Therefore, the aim of this paper is to determine properties of the masonry composite as a function of the properties of its components. The proposed methodology uses numerical analyses to obtain the material properties of a continuum smeared cracking model from discrete cracking models loaded in different directions. For that purpose, discrete cracking meso-models of masonry panels are subjected to tension and compression to numerically determine the stress-strain curves and the mechanical properties of the composite. For evaluation, material properties for the meso-models are taken from laboratory testing and from the literature. For model calibration, experimental tests on bricks, mortar and couplets are performed. The laboratory testing includes compression tests on masonry panels monitored with digital image correlation (DIC). Parameters such as the Young's modulus, tensile strength and tensile fracture energy for the masonry composite are determined for loading applied parallel and perpendicular to the bed joints.@en

Reinforcement corrosion is the most common and most expensive damage mechanism in existing reinforced concrete (RC) structures. Therefore, the qualitative and sustainable renovation of these structures leads to several important technical challenges. Camilo Torres, a student residence of KU Leuven built in 1968, is an example of a RC building dealing with corrosion problems. Corrosion causes the formation of rust and a reduction of the steel bar’s cross section. The former will eventually cause cracking and spalling of the concrete cover and deterioration of the bond at the reinforcement-concrete interface. An important question that can be asked is to which extent the corrosion process affects the structural capacity of the concrete components and how to deal with this in a renovation process. The focus of this paper is the on-site investigation of the corroded RC components of the Camilo Torres residence to provide input for structural assessment and renovation process. Firstly, the history of the building and used materials are investigated. Secondly, on-site analysis is performed to inventorise global and local damage. Results are compared with findings from previous on-site investigations executed in 2000 and 2014 to examine the damage progress. It was found that the main damage is caused by carbonation-induced corrosion leading to cracking and spalling of the concrete cover. An important part of the rebars have a concrete cover less than 25 mm due to construction errors. Also the presence of honeycombs accelerates the corrosion process. The Acoustic Emission technique is able to detect the damage patterns during tomography and passive acoustic emission sensing, however, more effort is needed to optimise the localisation accuracy.@en