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 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.

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.

Assessment of existing reinforced concrete (RC) structures after an earthquake is a challenging task that must somehow relate qualitative and quantitative observations in the plastic hinge regions and the associated residual deformation capacity of damaged structures. Having an estimate available for the remaining drift capacity will result in more economical and informed decisions regarding demolition or strengthening options. This study aims to develop a practical methodology to estimate the maximum drift demand of an RC column based on the residual crack width. For this purpose, fiber-based frame elements are used to model the RC column considering appropriately concrete behavior in compression and tension stiffening effects. Afterwards, the accuracy and reliability of the proposed methodology are demonstrated by validating the computational approach with two cyclic experimental results from literature and new test data for a one-bay one-story RC frame conducted within the course of this study. A comprehensive parametric study is performed for RC columns with different axial loads, longitudinal and transverse reinforcement ratios, and ground motions to exhibit the stochastic behavior. The study identifies the axial load ratio as the predominant parameter. Key findings include strong correlations between maximum drift ratios and total residual crack widths, as well as maximum compressive strains, with regression analysis yielding equations for accurate drift ratio estimation. Simple predictive models are proposed to estimate the maximum deformation demands based on observed residual crack widths. Residual cracking exceeding 5 mm poses significant risk for the columns with axial load ratios above 0.4, with 90% probability of exceedance 2% drift ratio.

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.

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.

The cracking of the pre-/post-casting UHPC joint in the steel-UHPC composite bridge deck system can lead to continuous tensile damage in the UHPC layer, reducing its ability to stiffen the steel deck. This study aims to clarify the cracking mechanism of the segmented-casting UHPC joint, and to provide design recommendations for cracking control. Axial tension tests on full-scale composite deck specimens were conducted, in which the influence of with and without joint, and varying reinforcement ratios on cracking response were identified. Moreover, the nonlinear numerical model for the composite deck, where the UHPC-UHPC interface was simulated in three methods, i.e. unbonded case, cohesive zone model (CZM), and perfectly bonded case, was developed and validated to simulate the crack initiation and propagation of the UHPC layer. Based on the validated numerical model incorporating CZM, improving the bond strength of CZM is more effective in controlling crack opening at the interface than increasing the failure displacement. Finally, optimized reinforcement arrangement and joint shape recommendations were provided to enhance construction convenience, minimize stress concentration, and limit crack opening.

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.

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).

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.

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.

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.

Proof load testing for assessment can involve a large risk due to the high loads. Stop criteria can reduce this risk. Stop criteria are necessary for shear, which is a brittle failure mode. This paper describes the development of shear stop criteria for slab strips. The shear stop criteria are developed by combining theoretical concepts related to cracking, as well the relationship between bending- and shear-critical regions, along with insights from the Critical Shear Crack Theory and the Critical Shear Displacement Theory. The shear stop criteria are validated with fourteen beam tests. The result is a set of shear stop criteria in a “traffic light system” with a green light level related to serviceability, and yellow and red light related to the ultimate limit state for shear. These stop criteria serve as the basis for a global approach for proof load testing of reinforced concrete bridges.