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Reinforcement corrosion induced by chloride penetration is a major threat to reinforced concrete structures in marine environments. The use of surface treatments to improve the durability of reinforced concrete structures has drawn increasing attention in recent decades due to their cost-effectiveness and convenience in construction. However, current knowledge of a practical, durable design to protect surface-treated concrete structures from chloride-induced steel corrosion remains insufficient. On this account, a rapid numerical approach was developed in this study to analyse the chloride diffusion in bilayer materials. In this approach, the time-dependency was considered for the chloride diffusion coefficients of both the surface-treated layer and the underlying concrete substrate and for the surface chloride content. The validity of this approach was verified with the finite element method and the computation time was only one hundred-thousandth that of the latter. This proposed approach makes it feasible in practice to estimate the probability of corrosion initiation in surface-treated concrete structures via Monte Carlo simulation. [ABSTRACT FROM AUTHOR]

Steel/concrete structures strengthened with externally bonded FRP plates may be subjected to significant temperature variations during their service time. Such temperature variation (i.e., thermal loading) may significantly influence the debonding mechanism in FRP-strengthened structures due to the thermal incompatibility between the FRP plate and the substrate as well as the temperature-induced bond degradation at the FRP-to-steel/concrete interface. However, limited information is available on the effect of temperature variation on the debonding failure in FRP-strengthened beams. This paper presents a new and closed-form solution to investigate the plate-end debonding failure of the FRP-strengthened beam subjected to combined thermal and mechanical (i.e., flexural) loading. A bilinear bond-slip model is used to describe the bond behavior of the FRP-to-substrate interface. The analytical solution is validated through comparisons with finite element analysis results regarding the distributions of the interfacial shear stresses, the interfacial slips and the axial stresses of the FRP plate. Given that a constant bond-slip relationship is adopted, it is observed that an increase in service temperature will lead to an increased interfacial slip at the plate end and consequently a reduced plate-end debonding load, and vice versa. Further parametric studies have indicated that the thermal loading effects become more significant when shorter and stiffer FRP plates are applied for strengthening. [ABSTRACT FROM AUTHOR]

This paper presents a methodology for numerically simulating the chloride diffusivity in mortar subjected to corrosion‐induced cracking with the aid of X‐ray microcomputed tomography (X‐ray µCT). In the research, the mortar sample with embedded steel rod was subjected to accelerated corrosion and then scanned by X‐ray µCT at consecutive corrosion periods of 0, 1,000, and 2,000 minutes. Upon the scanned CT images, a meso‐scale model consisting of multiple material phases with their intrinsic structures was built up and implemented into a finite element method for diffusion simulation. In the numerical simulation, the effects of multiple phases (void, crack, aggregate, rust, and interfacial transition zone between cement and aggregate) on the chloride diffusion of mortar are studied. Since the X‐ray µCT facilitates accurate local material information in time‐dependent and in situ manner, the diffusivity of mortar under different corrosion time and its spatial distribution characteristics (e.g., at different locations from the mortar surface) can be evaluated. [ABSTRACT FROM AUTHOR]

Abstract The precast concrete sandwich panel (PCSP) is a popular structural type used for prefabricated construction. In this study, three kinds of glass fiber reinforced polymer (GFRP) connector, including a flat plate, a corrugated plate, and a hexagonal tube connector, were investigated for potential use in PCSPs. In-plane direct shear tests were conducted to evaluate the performance of the connectors based on a typical push-out configuration (i.e., three concrete wythes linked with connectors and two rigid foam layers in between). Twenty-five specimens were tested, and the parameters investigated consisted of GFRP laminate thickness, projected length, and shear force direction. The shear force vs. relative slip relationships and failure modes of all types of connector were compared and are discussed in detail in this paper. Meanwhile, finite element (FE) analysis was conducted to reproduce the test results. All three types of GFRP connector exhibited a progressive failure manner in spite of the linear brittle nature of the FRP materials; the corrugated plate connector achieved higher deformability than the flat plate connector, particularly when the GFRP laminate thickness was small; and the hexagonal tube connector exhibited similar behavior along two orthogonal directions, making them well suited for use as two-way connectors. The developed FE model was able to well predict the peak shear load and stiffness of all types of connector based on comparisons with the test results. [ABSTRACT FROM AUTHOR]

This paper presents the development of a design approach for predicting the fire resistance of reinforced concrete (RC) beams exposed to design fire. The proposed method is based on the energy-based time equivalence method in combination with a correction factor that is formulated as a function of concrete cover depth and compartmental characteristics. In the proposed approach, the fire resistance period of an RC beam under design fire exposure can be deduced from that of the same RC beam under standard fire exposure; the latter can be predicted using a set of explicit equations previously developed by the authors. The fire resistance data of RC beams under design fire exposure, which were used to formulate and validate the proposed approach, were generated using a reliable finite-element approach. The proposed design approach is shown to be accurate in predicting the fire resistance of RC beams under design fire exposure. [ABSTRACT FROM AUTHOR]

Highlights: [•] Finite element (FE) modeling of RC beams exposed to fire was highlighted. [•] Particular attention was paid to the modeling of interfacial bond-slip behavior. [•] Comparisons between existing test data and numerical results were presented. [•] FE predictions provided a good understanding of the local behavior of RC beams under fire. [Copyright &y& Elsevier]

Allowing for the tension stiffening effects resulting from the bond between steel reinforcement and surrounding concrete leads to effective deformation analysis of reinforced concrete (RC) members when using a nonlinear finite element analysis modeled on the smeared crack concept. Nowadays, externally bonded fiber reinforced polymer (FRP) composites are widely used for strengthening existing RC structures. However, it remains unclear to what extent the tension stiffening of postcracking concrete is quantitatively influenced by the addition of FRP composites, as a result of the bond between the FRP and the concrete substrate. This article presents a discrete model, which is based on rigid body spring networks (RBSN), for investigating the tension stiffening behavior of concrete in FRP-strengthened RC tensile members. A two-parameter fracture energy-based model was deployed to represent the bond-slip behavior of the FRP-to-concrete interface. The reliability of the RBSN model was verified through comparisons with previous test results. Further parametric analysis indicates that the tension stiffening of concrete is hardly influenced by the addition of FRP composites before the yield of steel reinforcement has occurred although concrete crack patterns and crack widths may be influenced by the bond-slip behavior of the FRP-to-concrete interface. [ABSTRACT FROM AUTHOR]

Abstract: A post-tensioned negative moment connection technique is proposed to strengthen old multiple span simply-supported T-section reinforced concrete (RC) girders. In this technique, old concrete is removed from girder ends and flanges, a diaphragm is placed between the two adjacent girder ends over the interior support and negative moment steel strands are installed in new cast-in-place concrete and post-tensioned to make continuity. A total of six two-span simply-supported T-section RC girders were cast and five of them strengthened using the provision of the proposed post-tensioned negative moment connections. Both laboratory tests and nonlinear finite element (FE) analysis were conducted to investigate the structural performance of the strengthened RC girders. The moment redistribution in the strengthened continuous RC girders was also measured and is discussed. It is shown that the proposed post-tensioned moment connection technique can reliably transfer the negative moment over the support and markedly increase member stiffness and the load-carrying capacity of existing multiple span simply-supported RC girders. The validity of the FE analysis was also demonstrated through comparisons with experimental results. [Copyright &y& Elsevier]

• A one-dimensional multiphase model predicted well tensile behaviors of UHPFRC with various matrix strengths, fiber contents and geometries. • Physical-consistent strength and ultimate strain models of UHPFRC were proposed, trained by model-generated data and enhanced by experimental data. • The proposed strength and ultimate strain models predicted experimental data satisfactorily with mean absolute percentage errors (MAPE) of 12% and 25.3%, respectively. • Higher matrix strengths lead to higher tensile strength, less cracks with larger crack widths, and lower ductility of UHPFRC, due to snubbing effects and multi-crack interactions. Despite the rapid developments in fundamental investigations and engineering applications of ultra-high-performance fiber reinforced concrete (UHPFRC), there is still lacking of a reliable tensile stress-strain model for UHPFRC in design guidelines. A generalized tensile stress-strain model for UHPFRC was developed for the first time. Through properly identifying unified model parameters, widely acknowledged experimental results were successfully reproduced by using a one-dimensional finite element model (FEM). A rich database was generated and granted with physics by the FEM model. Physical-consistent strength, ultimate strain and stress-strain models of UHPFRC were proposed, trained by model-generated data, and enhanced by experimental data. The proposed strength model and ultimate strain model predicted extensive experimental results with reasonable accuracy, giving mean absolute percentage errors (MAPE) of 12% and 25.3%, respectively. The established stress-strain model also predicted satisfactorily the full-range stress-strain curves tested by different research groups. It was evidenced that higher mean matrix cracking strength leads to higher ultimate strengths, less cracks, higher crack widths of UHPFRC at the ultimate state. This was elaborated for the first time, as caused by the dual action of snubbing effects and multi-crack interactions. [ABSTRACT FROM AUTHOR]

The fire performance of reinforced concrete (RC) members strengthened with externally bonded fiber-reinforced polymer (FRP) laminates has been an issue of significant concern, particularly for building applications. To achieve structural fire-resistance ratings as specified in building design codes, an insulation layer often needs to be provided. This paper presents the first three-dimensional finite element (FE) approach for the fire performance simulation of insulated FRP-strengthened RC beams. The proposed approach gives careful considerations to the constitutive modeling of concrete, steel, and FRP, as well as the bond-slip behavior of FRP-to-concrete and steel-to-concrete interfaces. Comparisons between FE predictions and existing test data are presented to demonstrate the accuracy of the proposed FE approach. Numerical results obtained with the present FE approach show that the assumption of perfect bonding between FRP and concrete as adopted in previous numerical approaches leads to underestimations of deflections and thus unsafe predictions of fire resistance. The FE approach presented in the paper can be directly applied in performance-based fire safety design, or in parametric studies aimed at developing simplified design rules. [ABSTRACT FROM AUTHOR]

• Flexural performance of ambient-cured steel-reinforced geopolymer and ordinary cement concrete slabs were studied and compared. • Steel-reinforced geopolymer slab exhibited a smaller crack width and spacing. • The cracking load and initial stiffness of geopolymer slab are relatively low. • The Chinese codes of practice GB50010-2010 and ACI 318–19 can be used to predict the flexural capacity of steel reinforced geopolymer slabs. • The established finite element model can predict well the test results. This paper investigated the out-of-plane flexural performances of ambient-cured steel-reinforced slag and fly ash-based geopolymer concrete one-way slabs, in which the activator was the blend of NaOH and sodium silicate solutions (SiO 2 /Na 2 O = 3.1–3.3). Twelve specimens were prepared and tested, which included six OPC concrete specimens. The test parameters were concrete type (i.e., geopolymer and ordinary Portland cement (OPC) concrete), concrete compressive strength (i.e., 30 MPa, 40 MPa, and 50 MPa) and longitudinal tensile reinforcement ratio (i.e., 0.82 % and 1.20 %). The failure modes, crack patterns, load–deflection relationships and load–strain relationships of all specimens were carefully studied and reported. Further, a two dimensional (2D) finite element (FE) analysis was conducted to validate the test results. The results of the study indicated that: (1) the geopolymer concrete specimens presented lesser crack width and crack spacing owing to the improved bond between rebar and geopolymer concrete; (2) the cracking load and initial stiffness of geopolymer concrete specimens were slightly lower than that of OPC concrete counterparts; (3) the current Codes of Practice GB50010-2010 and ACI 318-19 provided reasonable predictions of the cracking load and flexural load capacity of the steel-reinforced geopolymer concrete specimens; (4) the developed FE model provided a good prediction of the flexural performance of the tested slabs, and could be used for further parametric investigation. [ABSTRACT FROM AUTHOR]

Despite the extensive investigations on the shear strengthening of reinforced concrete (RC) beams using externally bonded fiber-reinforced polymer (EB-FRP) composites, the critical problem of how the skew angle (angle between FRP and crack opening direction) influences the bond capacity of FRP has drawn little concern and remains unsolved. This paper presents the first three-dimensional (3D) finite element (FE) model for studying the failure of skew FRP-bonded concrete joints. The concrete was simulated using the concrete damaged plasticity model, and the FRP was modeled as an orthotropic material equipped with the LARC05 model as the damage criterion. The FRP-to-concrete interface was described using a linear elastic cohesive law. The 3D FE model, which provided a relatively large convergent mesh size of 2.5 mm, was calibrated and validated using the bond tests of aligned and skew FRPs. Both the tests and FE results revealed a notable decrease in the bond capacity of FRP at the skew angle of 45°. The parametric analysis demonstrated that the adverse skew effect was reduced when the FRP width increased or FRP thickness decreased, by delaying the onset of the stable peeling-off of concrete along the FRP fiber axis. Compared with FRP, steel plate suffered less from the skew effect, due to its isotropic nature. This study can provide valuable implications for more effective shear-strengthening methods of RC beams and facilitate novel insights for the development of more robust design models. The 3D FE framework can also serve as a versatile tool for analyzing the complicated failure modes of various FRP-strengthened concrete systems. • A three-dimensional FE model was developed for skew FRP-bonded concrete joints. • Non-zero skew angles could reduce notably the peak axial load of FRP during pullout. • The FRP bond width and FRP thickness have a significant impact on the skew effect. • Steel plates suffered less from the adverse skew effect due to its isotropic nature. • Regularized compressive stress-strain law is vital in CDPM for tension-shear failure. [ABSTRACT FROM AUTHOR]

• A modified concrete damaged plasticity model is proposed considering the deformation and mechanical characteristics of LRS FRP-confined concrete. • The 3D finite element analysis of longitudinal reinforcement buckling in LRS FRP-confined RC columns is realized. • The effect of longitudinal reinforcement buckling on member is illustrated by the FEA results. • The factors affecting the buckling of longitudinal reinforcement are studied, and an empirical formula for determining the failure of members by the buckling of longitudinal reinforcement is proposed. Large rupture strain (LRS) FRPs have great potential to be used for seismic retrofit of RC columns because of its high rupture strain (i.e., > 5%) that provides better confinement effects. However, in FRP-confined RC columns, the longitudinal reinforcements may buckle before the LRS FRP rupture, especially in the case of large stirrup spacing. This study aims to present a 3D finite element (FE) model for simulating the buckling effect of longitudinal reinforcements in LRS FRP-confined RC columns. A modified concrete damaged plasticity model (CDPM) is proposed to consider the deformation and mechanical characteristics of LRS FRP-confined concrete. Removal of failed concrete elements is considered to facilitate the buckling of longitudinal reinforcements in LRS FRP-confined RC columns. The FE analysis accuracy was verified by comparisons with test results. The factors affecting the buckling of longitudinal reinforcements were discussed through an extensive parametric study. Empirical formulas for the stress and strain values at which the longitudinal reinforcement starts to soften were developed. An empirical formula for the ultimate axial strain of LRS FRP-confined RC columns determined by longitudinal reinforcement buckling was also obtained by regression analysis. [ABSTRACT FROM AUTHOR]

Carbon fiber-reinforced polymer (CFRP)-retrofitted steel beams are likely exposed to significant service temperature variations due to seasonal and daily temperature changes. However, there is lacking research on the structural performance of CFRP-retrofitted steel beams under service temperature variations. This paper presents an experimental study of fourteen beams including one intact beam, one notched beam and twelve CFRP-retrofitted notched beams tested at various service temperatures from −20 °C to 80 °C. The structural properties including load–deflection curves, load capacities at initial and ultimate debonding, crack mouth opening displacements at the notch and the CFRP strain measurements were examined and compared at different service temperatures. The debonding loads of CFRP-retrofitted beams were increased with the temperatures from −20 °C to 60 °C and decreased at 80 °C. A formula was proposed to derive the local bond-slip behavior of the CFRP-to-steel interface at different temperatures from the CFRP strain measurements. The shear stiffness of the interface generally decreased with the service temperature growth, while the interfacial fracture energy first increased and then decreased. A finite element model was proposed to gain insight into the effects of interfacial thermal stress and temperature-dependent bond properties on the bond behavior and structural performance of CFRP-retrofitted beams at different service temperatures. [ABSTRACT FROM AUTHOR]

• Calibrating the concrete damage plasticity model by both the active confinement pressure approach and the confinement stiffness approach. • Deducing the concrete plastic flow from LRS FRP-confined concrete columns as a function of confinement stiffness. • Incorporating geometrical effects in the determination of the plastic dilation angle. In concrete columns confined with large rupture strain (LRS) fiber-reinforced polymers (FRPs), the LRS FRPs enhance the strength and ductility of concrete columns with the same mechanism as conventional FRPs by rendering passive lateral confinement pressure. However, LRS FRPs exhibit a strain capacity much larger than that of conventional FRPs. Notably, LRS FRPs have a bilinear material stiffness instead of the linear stiffness in conventional FRPs. Therefore, under axial compression, concrete confined by LRS FRPs will bear a different load path compared to that confined by conventional FRPs. This difference must be considered for finite element analysis (FEA) of LRS FRP-confined columns especially when the confinement pressure is non-uniform. To this aim, 23 samples of non-circular LRS FRP-confined concrete columns under axial monotonic compression were tested and analyzed. The variable test parameters are the aspect ratio (i.e., the depth (longer side) and width (shorter side) of the cross-sections）, the number of LRS FRP layers, and the type of LRS FRPs. For FEA, the concrete damage plasticity module (CDPM) was calibrated by both the active confinement pressure approach and the confinement stiffness approach. The active confinement pressure approach shows that the concrete plastic flow of LRS FRP-confined concrete is dominated by the secondary stiffness of the LRS FRP jacket. For the confinement stiffness approach, the concrete plastic flow is deduced from the compressive cyclic tests of cylindrical columns confined by LRS FRP jackets as a function of confinement stiffness. Results showed that the plastic dilation angle of concrete confined by LRS FRPs changes almost three times faster than that for concrete confined by conventional FRPs. The geometrical effects are included in the obtained plastic dilation angle so that a new plastic dilation angle model becomes feasible for the FEA of non-circular LRS FRP-confined concrete columns. Utilizing this new plastic dilation angle model enables the proposed plastic damage model to capture the stress strain behavior of the non-circular columns. Moreover, the non-uniformity of plastic flow on sections is captured reasonably. [ABSTRACT FROM AUTHOR]

Modelling of delayed failure of cut slopes in soft sensitive clays is a significant challenge because of three major features taking place simultaneously: large deformation of the slope up to failure, pore water pressure generation and dissipation in the slope, and complicated time-dependent deformation of sensitive clay. This paper proposes a novel fully hydro-mechanical coupled edge-based strain smoothed particle finite element (ES-PFEM) modelling approach for delayed failure of cut slope with three outstanding features: (1) the particle finite element method with low-order edge-based strain-smoothed element for large deformation analysis, (2) an efficient stabilization method for pore water pressure to circumvent the Babuška-Brezzi stability restriction and (3) the elasto-viscoplastic model considering time-dependency, anisotropy and destructuration of soft sensitive clays. The accuracy and efficiency of the proposed approach are first examined by simulating consolidation test and strip footing. Furthermore, an adaptive substepping algorithm is proposed for the elasto-viscoplastic model. Finally, a typical case of delayed failures of cut slopes with different angles in soft sensitive clays is simulated and analysed, demonstrating the predictive ability of the proposed approach. The relationship between slope angle, sensitivity of clay and time of failure occurring is obtained for predicting the slope failure time in practice. [ABSTRACT FROM AUTHOR]