The next generation of acoustic emission (AE) applications in concrete structural health monitoring (SHM) relies upon a reliable and quantitative relationship between AE measurements and corresponding AE sources. To achieve this, it is a prerequisite to accurately model the whole AE process that is a multiscale coupling process between local material fracturing and induced elastic wave propagation at structural level. Such a complex process, however, cannot be well addressed in currently available modelling methods. To fill this research gap, this study proposes a lattice modelling approach that achieves for the first time the explicit simulation of complete waveforms of transient AE signals induced by concrete fracture. The proposed approach incorporates an explicit time integration technique with a novel proportional-integral-derivative (PID) control algorithm for reducing spurious oscillations and a Rayleigh damping-based calculation and calibration method for the attenuation of AE waves. In this paper, the proposed lattice modelling approach is implemented to simulate the concrete Mode-I fracturing process in a three-point bending test. Besides the mechanical behaviors and AE hit number, a comparison was conducted between numerically and experimentally obtained AE waveforms. The AE waveforms and their attenuation characteristics simulated by the proposed lattice modelling method turn out to be comparable to experimental results. The proposed approach is of significance for a deep understanding of AE-related fracture mechanisms and a more reliable application of AE technique.

Aggregate interlock is considered one of the most important shear transfer mechanisms in concrete members. In the well-established Two-Phase model proposed by Walraven in the 1980s, the shear stress transferred by aggregate interlock is estimated by calculating the projected contact areas of two crack surfaces. As one of the main assumptions in the model, the crack surface is idealized by a plain surface crossing randomly distributed, idealized spherical aggregates. This was a necessary simplification of an actual crack surface in the 1980s because of the lack of measurement equipment as well as computational capacity. With the development of high-accuracy 3D scanning techniques, new possibilities for modelling aggregate interlock have become available. This paper proposes a generalised method to determine the aggregate interlock stresses using the crack surface directly from 3D scanning. The proposed method is cross-verified with the Two-Phase model using the same simplified crack surface. A case study using the scanned crack surfaces of concrete cubes is conducted to investigate the influence of surface roughness. The proposed method provides a new possibility for conducting a refined investigation of the aggregate interlock for new concrete types, especially under the scope of the next-generation Eurocode shear provision.

In the Netherlands, approximately 70 prestressed slab-between-girder bridges are present, built between the 1950s and 1970s. These bridges typically do not fulfil the requirements for shear in an assessment, but show no signs of distress upon inspection. Additional load-carrying mechanisms and effects of global bridge behaviour, such as compressive membrane action, compressive arch action, load (re)distribution, and the influence of the crossbeams, which could significantly enhance the structural capacity, are typically not considered in the assessment calculations. This paper studies the global structural behaviour experimentally of the full slab-between-girder bridge system as compared to the isolated T-girder. For this purpose, two spans of an existing multi-span T-girder bridge, the Vecht Bridge, built in 1962 were tested. In total, three experiments were carried out in span 4 (full system), and four experiments in span 2 (after applying saw cuts in the deck to create isolated girders). This paper reviews the state-of-the-art regarding collapse testing, global bridge behaviour, and slab-between-girder bridges in the Netherlands. Then, the results of the experiments are presented and analysed. It is expected that these experimental results will form the basis of improved assessment methods for slab-between-girder bridges in the Netherlands and beyond.

The authors regret that the Fig. 6a of the article was incorrect. [...]

Many existing concrete structures require effective assessment of the bearing capacity. A critical failure mode is shear, especially for concrete structures without or with limited shear reinforcement. The shear failure is brittle and often leads to loss of property and lives. Therefore the shear failure should be indicated before it occurs. A potential solution is to use acoustic emission (AE) monitoring, which is sensitive to minor changes in concrete, even micro-cracking, both on the surface and inside the structure. By combining the knowledge of shear failure processes and AE techniques, this paper presents an AE-based shear failure indication system. The system automatically identifies three levels of structural damage levels up to shear failure, which are categorized from minor to severe levels as green-light, yellow-light, and red-light criteria. The 'traffic light system' is validated using six shear tests on full-scale reinforced concrete beams without shear reinforcement. The robustness of the system is also validated across these tests.

During a proof load test on a bridge, high magnitude loads are applied. To avoid causing irreversible damage, thresholds to the structural responses, the so-called stop criteria, need to be defined. This paper proposes to categorize stop criteria into three levels: green light (related to the serviceability limit state), yellow light (related to potential irreversible damage) and red light (related to potential local collapse). For the Ultimate Limit State, stop criteria for shear and flexure are defined. Shear stop criteria are derived from mechanical models, using traditional strain measurements and acoustic emission measurements. These stop criteria are validated with experiments on reinforced concrete slab strips, straight slabs, and skewed slabs. The resulting traffic light system gives the bridge engineer a tool to make decisions during a proof load test. This approach is a step forward in the interpretation of structural responses during proof load testing.

Curved concrete crownwalls are commonly installed on vertical breakwaters in deep water to mitigate wave overtopping. This study compares the hydraulic and structural performance of fully curved and recurved crownwalls under impulsive wave loads induced by non-breaking waves, known as Confined-Crest Impact. Using one-way coupled numerical simulations in OpenFOAM and structural analyses in DIANA FEA, we assess the pressure fields and structural responses of the two geometries. Results reveal that while the fully curved crownwall significantly reduces overtopping, it experiences wave forces up to 2.5 times greater than the recurved crownwall, along with longer pressure impulse durations, leading to amplified tensile stresses and higher risk of cracking. In contrast, the recurved crownwall, despite localized peak pressures, benefits from a broader cross-section and linear stress distribution, resulting in better structural performance. These findings underscore the importance of integrating dynamic structural analysis in crownwall design to balance hydraulic efficiency with structural resilience.

Tunnel fires are relatively rare, but the consequences of damage can be large. This paper addresses the influence of tunnel fires on the ensuing damage to the concrete lining. To address this question, the existing literature is reviewed. This review focuses on different methodologies to get a well-rounded insight into the problem: relevant aspects of tunnel fire dynamics, theoretical considerations on the relation between the fire source and the resulting damage to the concrete, experimental evidences from testing concrete elements subjected to fire as well as data from tunnel fires that have taken place in the past, and insights from numerical analysis. The result is a comprehensive overview of what is currently known about the relation between a tunnel fire and the ensuing damage in the concrete, as well as guidance for the assessment of concrete tunnel linings under fire hazard and recommendations for future research to address the remaining open questions on this topic. To conclude, this paper gives a valuable overview based on different methodologies from the literature to give researchers, engineers, and asset owners a better insight in how fires can affect the concrete tunnel structure.

Reinforced concrete solid slab bridges are often skewed to cross underlying objects, which increases the shear stress concentration at the obtuse corner. Limited experimental evidence on skewed slabs is available, so that both the shear capacity and failure mode in skewed slab bridges are subject to discussion. Therefore, an experimental program at Delft University of Technology investigated the capacity and failure modes in skewed slabs under concentrated loads near the edge. Results from 15 tests on five 1:2-scale slab members result in shear failures and show a decreasing capacity with increasing skew angles. The obtuse corner is found to be critical; the reinforcement layout did not influence the capacity significantly. Comparisons with calculation methods showed reasonable accuracy. A proposed method using a larger integration length around the peak shear stress obtained from linear finite element modeling may be recommended for assessment.

The authors regret that the original publication of this paper did not assign the correct affiliations to R.D.J.M. Steenbergen. The authors would like to apologise for any inconvenience caused.

Despite the low probability of occurrence, fire events are a major hazard for structures, which can lead to severe socio-economic impact. Although reinforced concrete (RC) tunnels are an important component in transportation infrastructure, their structural behaviour under high temperatures is not yet fully understood. This study investigates the thermo-mechanical response of tunnels subjected to fire using nonlinear finite element analysis (NLFEA). For this purpose, recent experimental tests of large-scale reinforced concrete tunnels with and without fire protection are simulated. Different modelling strategies are discussed, and a detailed description of the constitutive model employed is presented. Then, model-to-model and model-to-experiment comparisons are conducted to identify the advantages and limitations of each approach. The analyses demonstrate the relevance of proper spalling modelling on the tunnel’s temperature distribution. The models also show a good agreement with the experimentally observed damage patterns. Finally, recommendations regarding modelling choices and further research topics are discussed.

As infrastructure continues to age and traffic levels intensify, there is a growing need for efficient methods to verify the reliability of many existing structures. Field testing offers the possibility to assess the current condition of a structure. Specifically, in a proof load test, substantial loads are applied to evaluate the structure's resistance to future loads that could compromise structural safety. However, to prevent excessive test loads and their potential damage, it is desirable to assess structural reliability by monitoring the response under more moderate loads. This study merges laboratory and in-situ testing results through a Bayesian update of the structural reliability after each successful load application. Two case studies are presented where laboratory testing on structurally similar elements and analytical modelling provide ample evidence to justify test load reductions of 20 % and 25 %. The proposed method offers a systematic framework to link the structure's response during testing to structural reliability and address the uncertainties in resistance, loads and measurements. Nonetheless, the representativeness of the data in terms of structural similarity and uncertainties related to measurements continue to be significant factors. Despite these challenges, incorporating monitoring data during proof load testing is expected to reduce target loads in most cases.

On the 17th of October 2021, a concrete grandstand element collapsed at the Goffert football stadium in the Netherlands under a jumping crowd load. In this paper the cause for the collapse is investigated from a probabilistic point of view. Various investigations raised some belief that the actual loads were larger than the design loads for the grandstand elements, also questioning the general reliability of these elements. There are also indications towards construction errors. This paper presents a full probabilistic method to determine the failure probability of the collapsed element in the Goffert stadium, subjected to dynamical crowd loads. Suitable distribution types and parameters of stochastic variables related to forces generated by jumping are derived. Randomly generated excitation signals are created that are used to excite the structure, which is modelled as a non-linear single-degree-of-freedom system with a bi-linear force-displacement relationship. A Monte Carlo simulation shows that 0 of about 105 simulations lead to failure of the structure under the crowd loading present during the collapse, if we would model it according to the design drawings. This result makes it unrealistic that the actual loads were higher than the design loads or that the design is unsafe since then we would expect a relatively large failure probability. In situ inspection of the concrete cover on other elements in the stadium show that large variation exists in this parameter, suggesting that the collapsed element could have had a large cover, which reduced its capacity. A sensitivity analysis concludes that the post-yielding stiffness highly influences the failure probability of the grandstand element. These two points combined make it more plausible that the element failed because the actual resistance of the structure was weaker than intended by the design drawings.

As the existing bridge stock is ageing in various parts of the world, the topic of how to assess, maintain and/or improve, and manage existing bridges becomes increasingly important. Existing bridges may be designed according to outdated codes with requirements that may be considered unsafe nowadays, and for loads that are significantly different than those used nowadays. For those bridges, an accurate assessment leads to more efficient management of the bridge stock. This paper outlines various strategies that lead to an improvement of the assessment, and potentially to the extension of the service life of existing concrete bridges. This paper provides a selected examples that engineers who are faced with the assessment of ageing bridge can use. Ultimately, the presented insights can serve to support countries with a younger bridge stock in the development of an assessment strategy.

Major fire events in tunnels have shown severe consequences in their structural performance, as reported in several incidents in the last decades. Particularly, due to the enclos-ure geometry of tunnels, intense thermal loading may develop in comparison to typical fires in buildings, which may result in more damage. Even though tunnel linings are an important com-ponent in transportation infrastructure, the understanding of their behaviour under high tem-peratures is limited. This paper aims to study the thermo-mechanical response of tunnels subjected to fire using nonlinear finite element analysis (NLFEA). For this purpose, recent experimental tests of large-scale reinforced concrete tunnels with and without fire protection are simulated. Different modelling approaches and strategies are discussed, and a detailed descrip-tion of the constitutive model employed is presented. The results obtained in the simulations indicated that the numerical analysis can be used to investigate the thermo-mechanical behav-iour of concrete structures.

In the Netherlands, there are about 70 prestressed T-girder bridges with cast-inbetween decks, constructed post-WorldWar II.While they have low ratings upon assessment, inspections reveal no distress. This research aims to understand the structural behavior of the full system compared to isolated T-girders. Experiments were conducted on the original structure, as well as on the structure with the deck sawn to test individual girder behavior. The main insight is that the system behavior at the ultimate limit state is driven by compressive membrane action in the deck as well as compressive arching action in the girders, and that simplified distribution factors for shear derived from linear elastic behavior do not properly reflect the distribution and load path at the ultimate. These results can be used for a better assessment of the existing pre- stressed T-girder bridges.

Aging infrastructure in the Netherlands presents a significant challenge, particularly with precast girder bridges made continuous, which exhibit inadequate shear reinforcement per current design codes. To address shear capacity and accuracy of current assessment practices, a research program including full-scale shear tests is underway at Delft University of Technology. As a part of the research, a blind pre-diction contest with two specimens has been organized. The experiments showed that the loss of composite action at the interface is the primary failure mechanism, and generally an accurate model of the interface behaviour in such composite members is missing. In this paper, a further review of the available interface models and previous tests is conducted. This review leads to the challenges in the accurate evaluation of the interface behaviour, as well as the next steps to address them: a new set of full-scale specimens, and a small-scale test setup reflecting a realistic stress distribution.

To date, there is no comprehensive approach available that can explicitly model the complete transient waveforms of acoustic emissions (AE) induced by fracture processes in brittle and quasi-brittle materials like concrete. The complexity of AE modelling arises from the intricate coupling between the local discontinuity of material fracturing and the global continuity of elastic wave propagation in solids. Among others, the lattice type models are promising approaches, as they are known to be a matured modelling approach to simulate the fracturing process in concrete-like materials. Nevertheless, like other discrete element methods (DEM), they are currently limited to describing the number and rate of AE events (broken elements) in the fracture process and cannot explicitly model wave generation and propagation. In this study, we propose a lattice modeling framework to simulate the propagation of complete waveforms of fracture-induced AE signals in concrete. A proportional-integral-derivative (PID) control algorithm is incorporated in an explicit time integration procedure to reduce dynamic noise from spurious oscillations. Additionally, a Rayleigh damping-based calculation method and corresponding calibration procedure are proposed to model the attenuation of AE signals due to material damping. Using the developed approach, we systematically investigate the feasibility of lattice models for elastic wave propagation simulation, the dependence of lattice mesh sizes and the choice of numerical damping parameters. These results lead to a systematic framework which can be employed in simulating wave propagation with attenuation using DEM models in general including lattice models.

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.

When employing the strut-and-tie modelling (STM) method in the conceptual design of reinforced concrete structures, a suitable strut-and-tie (ST) model indicating load transfer mechanisms first needs to be identified. Topology optimization (TO) methods have frequently been used for this purpose. However, although TO methods employing either a ground-structure or a continuum-based TO approach can be used, the performance and effectiveness of these two methods have not been systematically investigated and compared. To obtain a better understanding of the characteristics of both methods, a systematic comparison procedure is proposed to investigate the generation process and the resulting ST designs. Three aspects, relating to structural performance, economic issues, and method applicability are considered in the comparison, with six metrics formulated to quantify these aspects. Based on investigation of designs for three reinforced concrete elements incorporating typical discontinuity regions (two 2D cases and a 3D case), the performance of the two methods is assessed. It is found that both methods result in safe and efficient ST designs, with comparable structural performance, while some differences in terms of computation time and usability are observed.