This work presents a concrete-specific analytical framework for modelling body-wave scattering by explicitly tailoring multiple-scattering theory to the microstructural characteristics of concrete. Instead of treating scattering parameters as abstract statistical quantities, the framework parameterizes the key inputs of scattering theory in terms of physically measurable concrete attributes, including coarse aggregate size, volume fraction, and the material property contrast between the matrix and the dominant scattering phase, whether coarse aggregates or the interfacial transition zone. By embedding these microstructure-informed parameters into a two-phase spatial statistical formulation, closed-form expressions for total and transport scattering cross-sections are derived and directly linked to ultrasonic diffusivity through diffuse wave theory. Experimental validation using geopolymer concrete members and published data for ordinary concrete demonstrates consistent agreement between theoretical predictions and experimental measurements across a broad frequency range. The proposed framework therefore renders body-wave scattering in concrete quantitatively computable from material composition, providing a physically grounded basis for quantitative interpretation of diffuse wave transport, energy equilibration, and coda-wave velocity changes without reliance on ad hoc fitting parameters.

Proof load testing can be used to directly assess bridges. Over the past six years, fundamental research has been carried out at Delft University of Technology to derive mechanics-based shear stop criteria and to enable structural reliability updating via Bayesian methods. To translate these research findings into recommendations for practice, aspects related to determining the target load, location of the load, location of the sensors, and practical implementation steps have been addressed. This paper illustrates these recommendations with a hypothetical case study showing the influence on the preparation and execution of proof load tests. The result is practical guidance for proof load testing, demonstrating how information sources can be combined to achieve minimal target loads. While application via a full-scale test is pending, these recommendations reflect the latest research insights into proof load testing and its implementation strategies.

Proof load testing on bridges requires high magnitude loads. Stop criteria are used to avoid irreversible damage or failure during proof load testing. These stop criteria are thresholds to measurable parameters during the test. After reaching a stop criterion, the proof load test needs to be terminated. While in the past, stop criteria have been identified as a single level, this research proposes to use a traffic light system for stop criteria: green light (related to the serviceability limit state), yellow light (as an intermediate level) and red light (further testing is not permitted). The green light relates to the development of cracking, whereas the yellow and red light relate to the failure modes of flexure and shear. To develop stop criteria for the brittle failure mode of shear, thresholds are derived from mechanical models, based on strain measurements and crack widths, as well as using acoustic emission measurements. To validate the stop criteria, three series of experiments are analyzed: reinforced concrete slab strips, straight slabs, and skewed slabs. While field validation of the traffic light system is pending, the developed tool is a step forward to safely test concrete bridges without shear reinforcement.

Submerged floating tunnels are more and more considered as a suitable solution to cross water channels limiting environmental impact on the visual landscape and ensuring large ship passage while crossing large distances between coasts. The design of this kind of strategical infrastructures must deal not only with live loads and particular loading condition coming from the floating situation but needs also to carefully consider accidental actions that concur to the global safety of the infrastructure. The construction of the new E39 highway along the Norwegian coast asks for crossing several fjords and this solution is seriously taken into consideration. For this reason, a comprehensive research programme was aimed at the analysis of accidental load design of the infrastructure. This paper aims to present a comprehensive overview of an ad-hoc experimental investigation on the behaviour of reinforced concrete (RC) circular slabs (60 cm diameter) under exposure to fire, blast, or a combination of both actions. Additionally, it seeks to draw design-driven conclusions that could be valuable for the design of critical infrastructure in scenarios involving fire and blast. The presented experimental campaign was intended to provide a benchmark for assessing the reliability of the design approaches to be adopted in the design of the global infrastructure. First, the concrete mechanical characterisation at normal condition and at high temperatures was performed referring both to the uniaxial compression and uniaxial tension. The structural behaviour of simply supported RC slab has been also investigated by considering slabs exposed to a hydrocarbon fire curve at different exposure times and by considering the post-fire application of static or dynamic loading condition. In particular, the fire curve was applied by a gas burner while the dynamic load was reproduced by a shock tube equipment that was used to apply two different blast-like pressure histories.

Distributed Fiber Optic Sensors (DFOS) have gained relevance in the study of concrete structures due to their ability to provide quasi-continuous strain measurements with high spatial resolution. These sensors, which can be either surface-mounted or embedded, overcome the spatial limitations and sparse data offered by conventional discrete methods. This study explores a novel application of DFOS: quantifying relative sliding in concrete-to-concrete interfaces. A large-scale experimental campaign at Delft University of Technology investigated the structural behaviour of a precast prestressed girder and a cast-in-situ top layer, with an interface between the two components. The critical role of the interface in the structural behaviour and failure mechanism of the specimens, combined with the complexity of the boundary conditions, requires more detailed measurements of the failure process at the interface. To achieve this, DFOS were embedded in the specimen on both sides of the interface of interest. Strain measurements were obtained during static tests, and relative sliding was calculated from the differential strain profiles. The DFOS results were compared with discrete measurements from Linear Variable Differential Transformers (LVDTs) and Digital Image Correlation (DIC). The findings highlight the potential of DFOS to provide a refined characterisation of the sliding behaviour of concrete-to-concrete interfaces, to deliver additional insight into the spatial evolution of interface strains, and to support the identification of load-transfer mechanisms, such as dowel action.

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.

Bridges are among the most important infrastructure assets, especially reinforced concrete slab bridges. Many were built with a skew angle instead of straight due to the limited space available. The skewness affects the internal shear force distribution of the slabs and causes shear stress concentration at the obtuse corner. Most of the shear design methods are developed based on straight slabs. Whether these methods apply to skewed slabs is unclear. On the other hand, experiments on skewed slabs are quite limited. Therefore, an experimental programme of skewed slabs was conducted at Delft University of Technology. The slabs have a height of 300 mm, representing a half-scale model of representative solid slab bridges in the Netherlands. A concentrated load was applied close to the edge of the slabs to induce a one-way shear failure. Both the top and bottom surfaces of the slabs were measured using stereo Digital Image Correlation (DIC). This paper presents the design and the results of the experiment. By using the stereo DIC from both surfaces, the internal shear crack propagation is captured. All specimens failed in shear and the results demonstrate that the shear capacity of the slabs decreases as the skewness increases. Moreover, the experiment confirmed that the shear stress concentration is more significant in the obtuse corner than in the acute corner. An evaluation method is proposed to calculate the shear capacity of the skewed slab combined with the Linear Finite Element Analysis. The calculated shear capacity given by the proposed method shows a good alignment with the experimental results.

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.