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• The numerical model's setup for the steel fibre reinforced concrete (SFRC) segment. • Numerical simulations of GPR detection for SFRC segment under different conditions. • Optimum frequency selection of the SFRC segment. • Validation of an SFRC segment detection based on a model test. • Calculation of the equivalent relative dielectric constant (ERDC) of SFRC segments. The SFRC segment is gaining attention in shield tunnels due to their better mechanical properties. However, the existence of steel fibres poses a greater difficulty when attempting to utilize ground penetrating radar (GPR) for nondestructive quality inspection compared to conventional reinforced concrete segments. This paper presented a refined numerical model of SFRC segments with gprMax software, to investigate the penetration characteristics of GPR. The numerical model incorporated four different steel fibre contents, namely 0%, 0.5%, 2.5%, and 5%. The model also included an internal void and a surface metal plate to compare and analyze the waveform characteristics of GPR with the normal sections of the segment. The orthogonal test of numerical simulation investigates the imaging characteristics, power attenuation patterns, and imaging features of three different GPR frequency gradients: 200 MHz, 500 MHz, and 1000 MHz. This analysis helps in selecting the appropriate detection frequency based on the observed energy attenuation patterns and imaging characteristics. Then, the model test was conducted at the selected frequency to study the penetration performance of GPR. The research results indicate that the numerical model established in this paper demonstrates good effectiveness in studying the waveform characteristics of steel fibre-reinforced concrete under various conditions. The numerical model established in this paper realized the study of the penetration characteristics and imaging features of different steel fibre contents, GPR frequencies, and detection targets. Analysis of waveform characteristics, power attenuation, and imaging results indicates that GPR at 500 MHz exhibits better detection performance for SFRC segments. The results of the numerical simulation were verified through model tests of real SFRC segments, demonstrating that 500 MHz has good penetration performance for SFRC segments. This paper also proposed a calculation method for equivalent relative dielectric constant (ERDC) based on the model test results and validated its rationality through the analysis of numerical simulation results and real GPR waveforms. [ABSTRACT FROM AUTHOR]

For fiber reinforced permeable concrete, numerical simulation method have been applied to reduce the time consumption of physical experiments and to study the mesostructure of the material. In this paper, polyacrylonitrile fiber reinforced permeable concrete (PANFRPC) is considered to consist of aggregate, mortar (containing fibers inside), interface transition zone (ITZ) and pores in 3D mesostructure model generated from computer tomography (CT) images. For the numerical simulation of the, material properties of each component in the model are assigned according to physical experimental results. The failure curve of the mortar in PANFRPC is determined by physical test results to reflect the effect of fibers. The simulation results show that the model has similar mechanical properties to the actual specimen and can be used to simulate the elastic stage of the uniaxial compression process and predict the strength with an error of less than 15% despite the simplification of fiber. the accuracy and reliability of the model have also been verified by the distribution pattern of vertical caraks and x-shaped shear cracks from macro and meso perspectives. • CT scanning and digital image processing technology are applied to extract the mesoscopic components of PANFRPC specimen. • 3D mesostructure model of PANFRPC is established for numerical analysis of uniaxial compression process. • The accuracy and reliability of the numerical model construction method are verified by simulation results. [ABSTRACT FROM AUTHOR]

• A numerical simulation method for the multifactor coupling of stress field and temperature field is developed. • The numerical simulation method is in good agreement with the experiment results at elevated temperatures. • The numerical simulative description of the grout material failure and fracture of a steel bar. • Prediction of the yield point and the ultimate point of FGSC from 25 °C to 1000 °C. Fire is one of the main objects of study at the cutting edge of the research on disaster prevention and mitigation in structures. In the event of a fire, the mechanical properties of the structural material will be significantly reduced, resulting in serious consequences. This paper simulates the tensile properties of sleeve grouting members at five different temperatures, to contribute to the research here. The simulated member stress-strain curves fit well with the corresponding experimental results. The paper introduces constitutive models of concrete, steel, and sleeve. Beyond that, a feasible finite element model of the grouted sleeve is proposed. Two special points' (yield point, ultimate point) coordinate formulas which are related to different temperatures (25–1000 °C) are presented. It indicates the regularity of fully-grouted sleeve tensile force-displacement curves in various temperatures. Meanwhile, the research content provides the basis for further research on reinforcing bars spliced by grout-filled coupling sleeves. [ABSTRACT FROM AUTHOR]

• A cohesive zone model is established to simulate the fracture behavior of bi-material Brazilian disks. • The failure patterns of rock-concrete bi-material Brazilian disks affected by interface morphology and loading angle are obtained. • Analyze the failure mechanism of rock-concrete bi-material Brazilian disks. As the most fragile component in a bi-material structures, the performance of rock-concrete interface will greatly affect the stability and durability of the whole structure. To investigate the influence of interface morphology on the interface bearing capacity and fracture characteristics of bi-material Brazilian disks, the sandstone-concrete bi-material Brazilian disk is taken as the research object, a series of sandstone-concrete bi-material Brazilian disks with interfaces of different groove widths, depths and spacings are simulated based on the cohesive zone model (CZM) method in this paper, and the effects of loading angle and location of groove interfaces on the fracture behavior are also investigated, the loading rate of all models is 0.1 mm/min. The loading angle is the main factor affecting the fracture patterns of the bi-material Brazilian disks. The loading angle increases from 0° to 90°, and the failure patterns can be divided into sawtooth fracture along the groove, mixed mode of sawtooth fracture along the groove and tensile fracture of the matrix, and tensile fracture of the matrix. The interface is the main bearing part at small loading angles, and when the loading angle exceeds 30°, the matrix is the main bearing part, and at this time, the morphology of the interface has little influence on the failure patterns and bearing performances of the specimens. The groove interface significantly improves the bearing capacity of the interface, in which the groove width has the greatest influence on the bearing capacity of the interface, and the groove spacing affects the location of crack propagation along the sawtooth (rock sawtooth or concrete sawtooth). The location of the groove interface affects the crack propagation mode at the interface, and this study mainly presents three cracking modes: failure along the rock sawtooth, failure along the concrete sawtooth and the combined failure of the rock sawtooth and the concrete sawtooth. [ABSTRACT FROM AUTHOR]

• Coupled transport model of sulfate–chloride salts in concrete is established. • Chloride ions' adsorption and desorption capacities are considered in model. • The effect of interaction concentration of SO 4 2− and Cl− is quantified. The transport of sulfate–chloride salts in concrete is the main cause of its structural deterioration. Traditional numerical simulation assumes that the diffusion coefficients of sulfate ions and chloride ions are both constant leading to large deviations in the predicted results. Based on the mass conservation law, Fick's second law, and the theory of porous media, a variable coefficient transport model of sulfate–chloride salts in concrete is established in this paper. The model fully reflects the adsorption and desorption of chloride ions in the transport process, the reaction-filling process of sulfate ions and hydration products, as well as the most important porosity and tortuosity affecting ion transport. Results show that the prediction results of the two-dimensional variable coefficient model are consistent with experimental and literature results, with maximum error of 23.49%. The analysis of influencing factors shows that the interaction between sulfate ions and chloride ions does not change the transport law of ions in concrete, but delays the rate of ion corrosion within about 700 days. The ability of chloride ions to be adsorbed decreases by about 20% when sulfate ions are present, and the desorption rate is about 40% to 60%. The tortuosity decreases with the increase of water-binder ratio, and increasing the initial porosity from 5% to 12% leads to an early appearance of cracks by about 1400 days. [ABSTRACT FROM AUTHOR]

• Numerical simulation of hydration heat transfer and thermal stress in early-age concrete. • Investigating different mitigation strategies including: placement time during a day, lowering placement temperature, using heat blankets, changing type of aggregates, optimizing the mix, utilizing cooling pipes, and sequencing pours. • Minimizing risk of thermal cracking and delayed ettringite formation in mass concrete pours. Early-age thermal cracking and delayed ettringite formation (DEF) are short-term and long-term major issues to the durability of mass concrete and require a high level of consideration in the development of a suitable concrete mix design in placement and curing strategies, particularly in mixes of high cement content. Where DEF risk proves to be significant, contractors are required to adopt risk mitigation strategies including lowering concrete's temperature during placement by adding cool water or ice, for example, to the mix, embedding cooling pipes in the cast element and/or sequential placement of the concrete. These strategies can be implemented at different levels, as needed, to minimise the risk of cracking and DEF. Determining the most suitable and cost-efficient risk mitigation strategy, however, together with its implementation, is a complex task that requires consideration of each complex strategy under project-specific conditions. While a significant research effort has been invested to develop an improved understanding of the effectiveness of different early age thermal cracking and DEF risk mitigation strategies, the lack of reliable models capable of simulating and comparing the effectiveness of all scenarios remains elusive and considerably limits the ability of the practitioners in identifying the optimal approach. This paper presents a Multiphysics model developed to predict the effect of early-age thermal cracking and DEF risk mitigation scenarios. The model is validated using four real-life project Case Studies and is demonstrated to provide reliable results. In addition, the paper studies the comparative effectiveness of key risk mitigation strategies and the important parameters influencing their effectiveness. [ABSTRACT FROM AUTHOR]

• Push-out tests of SRRAC. • The basic model of bond stress-slip curve. • Calculation formulas of bond strengths. • The bond stress-slip full curve equation. • Finite element analysis of bond-slip performance. The steel reinforced recycled aggregate concrete (SRRAC) is a kind of composite building material, and the bond performance at the interface determine the mechanical properties of the composite material. The purpose of this paper is to explore the bond performance of SRRAC. First, 43 SRRAC push-out specimens were made, and push-out tests were conducted on them. It was found that the failure process has gone through four stages. The failure patterns were found by analyzing all cracks, and the mechanism of the cracks was analyzed from the mechanical level. The basic model of load-slip curve was proposed. Secondly, the basic model of bond stress-slip curve was proposed, which was divided into four segments by three key points. The bond strength and slip of the three key points were respectively defined, and their respective calculation formulas were obtained through statistical analysis methods, which were verified by the test. Then, this paper proposed the bond stress-slip full curve equation, which was well verified by the test. Finally, detailed finite element analysis was carried out on SRRAC specimens, and the reliability of the model and the bond stress-slip full curve equation was further verified by the test. [ABSTRACT FROM AUTHOR]

• Statistical homogenization method is effective to equivalent porous meso -element. • Meso-element size has no significant influence on ascent stage of stress–strain curve. • Convergence stress of descending stage decreases with increase of meso -element size. • With increase of porosity the deformation ability of cellular concrete enhances. The novel cellular concrete with millimeter-size isolated spherical pores can greatly reduce the transportation cost of concrete coarse aggregate in the construction of facilities on remote islands, which utilizes spherical saturated SAP (Super-Absorbent Polymer) presoaked in seawater in situ. The mechanical property of this cellular concrete is an important basis for its engineering application. The purpose of this paper is to present a numerical method to understand more fully and efficient ly its mechanical properties. According to the characteristics of meso -component of this cellular concrete, the meso -element equivalent model is improved, in which statistical homogenization method is used to substitute Voigt equivalence method. Based on the elastic damage constitutive model, uniaxial compression numerical tests are carried out on random meso -elements, and the parameters of damage constitutive model related to the porosity are obtained. On this basis, the random specimen model is divided into meso -elements of the same size, and the equivalent mechanical properties are given to the elements according to their porosities. The effectiveness of the numerical simulation method is verified by comparing with the actual test results, and it can reflect the damage process during uniaxial compressive loading. [ABSTRACT FROM AUTHOR]

• Compared with ordinary Portland concrete, geopolymer concrete show strong advantage in resisting chloride ion penetration. • Ions' initial concentrations have significant effects on the transmission speed of ions in pore solution. • Under the action of externally applied electric field, the ion electromigration plays a leading role, presenting a rectangular wave in the concentration distribution curve. • The boundary conditions and ions' diffusion coefficients have large effect on the increasing or decreasing rate of ions. This paper presents a numerical investigation on the penetration of chloride ions in a saturated geopolymer concrete under the action of externally applied electric field. The chloride ion transport model in geopolymer concrete is established, and the interactions between different ionic species such as potassium ions, sodium ions, hydroxide ions, and chloride ions are considered. By solving the modified mass conservation equation and the Poisson equation of individual ionic species, the concentration and electrostatic potential of different ions at any position and at any time are obtained. Results show that under the action of externally applied electric field, the ion electromigration plays a leading role, which is characterized by a rectangular wave in the concentration distribution curve. In addition, the average chloride ion penetration depth obtained from the numerical simulations agrees well with that measured from the experiment in the cited literature. Moreover, the transmission speed of the two positively charged ions (or the two negatively charged ions) are almost the same. While there is a striking difference in the transmission speed between the positively charged ions and the negatively charged ions, indicating that the electrostatic potential gradient is not constant, and is region related. [ABSTRACT FROM AUTHOR]

• The shear strength of the shot-earth 772-granite interface is numerically investigated. • The Lattice Discrete Element Method is used. • A novel constitutive law considering friction between the crack faces is implemented. • The shear strength is estimated by varying the normal pressure. • A detailed analysis on damage evolution is performed. In the present paper, the shear strength of the shot-earth 772-granite interface is simulated through a numerical Lattice Discrete Element model, since there is no experimental data available in the literature relatively to such a property. To such an aim, a new constitutive law for the discrete elements is proposed, which allows to capture the dissipated energy due to the damage produced by both material degradation and frictional sliding along rough crack surfaces. Firstly, the model is calibrated by considering a direct shear testing between a shotcrete and a granite. Then, the model is applied to simulate the shear strength of the shot-earth 772-granite interface. The shear strength is estimated by varying the normal pressure, and a detailed analysis is performed on the damage evolution. [ABSTRACT FROM AUTHOR]

• A DEM pavement paving compaction model is developed. • Digital aggregate database is established by using imaging technology. • The aggregate database is expanded via AI method. • The paving compaction model is calibrated and then used for compaction analysis with different aggregate gradations. Pavement compaction cannot be neglected during the motorway manufacture stage because it can determine pavement service quality and durability. Concerning the compaction scenario, the paving compaction is responsible for offering the preliminary strength of the pavement. Ignoring paving compaction quality control can lead to over compaction. This paper introduces an integral system to study and simulate the paving compaction of asphalt motorways in Discrete Element Model two-dimensional (DEM2D). This method includes the whole procedure from aggregate image acquisition database establishment to the DEM2D simulation of paving compaction. To this end, this study fulfils the creation of the aggregate database applied in DEM via the Aggregate Image Measuring System (AIMS) method. In addition, the artificial intelligent (AI) technology called Generative Adversarial Networks (GANs) method is proposed to expand the developed DEM aggregate database. Three different approaches are applied to calibrate the accuracy of the extended database. According to the aggregate database, the pavement paving compaction with different aggregate gradations can be simulated in DEM2D. [ABSTRACT FROM AUTHOR]

• Numerical methods to simulate nonlinear behaviors of a novel H-type end anchored (EA)-FRP system are established. • Interface adjusting mechanisms of H-type EA-FRP system and its strengthening mechanisms on RC beams are investigated numerically. • Simplified design formulas for predicting the ultimate deformation of RC beams strengthened by H-type EA-FRP system are proposed. • Strain relaxation caused by interface slip is considered when calculating the ultimate deformation. A ductile end anchorage (EA) system for fiber-reinforced polymer (FRP) sheets using H-type anchors has been recently proposed to compensate for the loss of deformation capability of externally-bonded FRP strengthened reinforced concrete (RC) beams. The effectiveness of the novel anchorage system has been verified by existing experimental results, while there still lack of deep investigations on its strengthening mechanisms and quantitative evaluations of the deformation capability. Against this background, high-fidelity finite element (FE) models of FRP-plated concrete members and RC beams with H-type end anchors are developed using LS-DYNA in this paper. The most proper simulation approach is identified through comparing with the experimental results. Based on the validated FE model, the mechanical behaviors and strengthening mechanisms of the end anchorage system are investigated thoroughly. Extended parametric studies are conducted to study the influences of FRP thickness and the width of the anchorage deformation section on the strengthening effectiveness. Based on the findings in the numerical simulation, the strength model of EA-strengthened beams is improved, and an analytical model for predicting the ultimate deflection of EA-strengthened beams is established. [ABSTRACT FROM AUTHOR]

• Experimental and numerical investigation of GLT beams exposed to fire is presented. • The temperature field is recovered using FEM simulation and Bayesian inference. • Parameters of simple charring rate models are improved using Bayesian inference. • Proposed approaches open the door to stochastic analysis of GLT beams loaded by fire. This paper presents a combined experimental and numerical investigation of the behavior of glued laminated timber beams when exposed to fire. The influence on the time variation of charring rates based on the evolution of temperature profiles is examined for different fire scenarios and durations as well as different beam's cross-section sizes. Predictions of charring depths provided by numerical simulations of heat transfer and simplified charring rate models are compared. In the absence of a mass transport representation, a Bayesian inference is introduced to identify the temperature-dependent material parameters for the conventional heat transfer model. A similar approach is adopted when adjusting the selected parameters of the charring rate models to account for variations in actual fire scenarios, which potentially depart from standard fire exposure. When compared to experimental results, both approaches confirmed their predictive capabilities, particularly in the stage of initial design. Since presented in the framework of Bayesian statistics, they open the door to fully stochastic analysis with an emphasis on the load bearing capacity of the studied beams. [ABSTRACT FROM AUTHOR]