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.

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.

Inverted T precast girders with a cast-in-situ topping layer, recognized as precast composite girders, are commonly used in Dutch bridge construction. Notably, the bridges built before 1974 often lacked sufficient shear reinforcement, raising concerns about their shear capacity under increasing traffic loads. However, how to assess these composite girders under the scope of the second-generation Eurocode remains challenging, as the shear formulations were originally developed for monolithic structural members. Consequently, their direct applicability to precast composite systems, due to the distinctive stress distribution in the web of the composite structural members, lacks theoretical substantiation and experimental validation. This study first presents the three alternative failure criteria equations based on the same theory, and after that, an experimental investigation of the shear behaviour of precast composite girders through two full-scale tests is discussed. The test data is later used to compare the alternative failure criteria.

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 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.

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.

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.

Alkali-silica reaction (ASR) can pose a serious threat to existing reinforced concrete (RC) structures. ASR manifests as expansion leading to both additional load effects in the structure and material deterioration, which for structural members can lead to cracking of concrete and yielding of the reinforcement. The free ASR expansion is influenced by restraints from both external loading and internal reinforcement, a phenomenon known as restrained ASR expansion, which is anisotropic. A reliable method that can simulate the effect of ASR on a structural scale as a function of time is needed. The starting point of this modelling approach is free ASR strains that for instance can be deduced from cyclic compressive tests on extracted cylinders from the structure under investigation, frequently denoted Stiffness-Damage Testing (SDT). Furthermore, using the ABAQUS FE platform, a user subroutine to simulate the restrained ASR expansion strain in ASR-affected RC members was developed. Based on this programming, 3D finite element analyses on prism specimens with external loading or internal reinforcement were conducted. The results were compared and validated against experimental measurements. This investigation is part of a large project, denoted as MESLA, where the major objective is to obtain a more reliable assessment of ASR-affected concrete structures by coordinating inspection, material testing, and structural strength analysis.

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.

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.

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.

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.

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.

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

This paper proposes a new mechanical model to describe the dowel action with the aim of using the model to gain a deeper understanding of the unstable dowel splitting cracking observed in shear experiments of beams without shear reinforcement. The model was developed by combining beam on elastic foundation (BEF) theory and fracture mechanics. The proposed model is able to predict the whole evolution process of dowel action until the propagation of the dowel splitting crack becomes unstable. The model theoretically proves that the development of a dowel splitting crack can become unstable under certain conditions, therefore leading to the unstable shear failure of the whole member. In addition to the derivation of the analytical model, the paper also validates the model using data from the literature. Finally, an analytical solution of the critical shear displacement that triggers the unstable dowel splitting crack is derived. It can be used to improve the failure criterion initially proposed in the Critical Shear Displacement Theory (CSDT).

Given the ageing infrastructure, verifying the reliability of existing structures is crucial. Field testing presents a viable approach to evaluating a structure’s current condition, particularly proof load testing. In a proof load test, a large load is applied to assess its reliability. Structures in sound condition are expected to display satisfactory behaviour under average load intensities. Can good structural performance under moderate load levels already prove sufficient structural reliability? The proposed method utilises data from laboratory tests on similar structural elements. A case study was conducted on a bridge to illustrate the effectiveness of the method. Data acquired from laboratory tests were pre-processed to provide the required input for the reliability updating. It reveals that sufficient reliability can be demonstrated without excessive load levels by incorporating laboratory data. However, the actual capacity of the bridge and the uncertainty associated with the laboratory data remain important factors.

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.

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.

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.

Dowel action is recognized as one of the major shear resistance mechanisms. Although the dowel action only contributes a relatively small portion of the total shear resistance, the shear failure of reinforced concrete members without shear reinforcement usually occurs accompanied by unstable dowel cracking. This paper presents a new description of the dowel splitting process and a mechanical model based on two theories, namely the Beam on Elastic Foundation (BEF) theory and fracture mechanics. The mechanical model analytically describes the three stages during the dowel splitting of the longitudinal rebar in an RC beam, which are the elastic stage, stable cracking stage and unstable cracking stage. The proposed model can capture the post-peak behaviour of the nature of dowel action. Finally, a simplified equation for engineering practices is proposed. The proposed expression shows promising agreement with the experimental data.