Search Results (731)

This study investigates the structural behavior of steel I-beams containing corrosion-induced section loss and web openings, along with the effectiveness of fiber-reinforced polymer (FRP) strengthening as a retrofit strategy. Although previous studies have investigated the effects of corrosion, web openings, and FRP strengthening in steel beams, limited attention has been given to comparing the structural response of slender and deep steel beams under these deterioration scenarios and assessing strengthening strategies according to their distinct failure mechanisms. The analysis considers two structural response regimes: slender beams governed predominantly by flexural behavior and deep beams where shear deformation plays a significant role. Three-dimensional (3D) nonlinear solid finite element (FE) models are developed to evaluate the influence of corrosion location, web opening position, and FRP-strengthening schemes on load-carrying capacity and failure behavior. The results indicate that corrosion-induced flange thinning significantly reduces flexural capacity in slender beams, while web degradation has a comparatively smaller effect. FRP strengthening of the tension flange is found to be the most effective strategy for restoring flexural performance in slender beam configurations. In contrast, deep beams exhibit higher sensitivity to shear-related damage, where web openings located in shear transfer regions lead to substantial reductions in load capacity. Strengthening of the web region using FRP significantly improves shear resistance and overall structural performance. Overall, the study highlights distinct differences in damage sensitivity and strengthening effectiveness between slender and deep beam responses under corrosion and web opening effects, providing practical guidance for condition assessment and retrofit design of deteriorated steel I-beams. Full article

Concrete-filled steel tube (CFST) structures are widely used in modern infrastructure due to their superior strength, ductility, and composite action. However, long-term corrosion of the steel tube, particularly under aggressive environmental conditions, poses significant challenges to their durability and structural performance. This study presents a comprehensive review of corrosion mechanisms and mitigation strategies for CFST structures. The primary corrosion processes, including general corrosion, localized (pitting) corrosion, and circumferential corrosion, are critically examined with emphasis on the influence of chloride ingress, carbonation, marine exposure, and combined environmental actions such as freeze–thaw cycles and sustained loading. The effects of corrosion on structural behavior are analyzed in terms of load-carrying capacity, ductility, buckling resistance, and failure modes. A systematic evaluation of existing mitigation strategies is conducted, encompassing material-based approaches, protective coatings, cathodic protection systems, and structural strengthening techniques such as fiber-reinforced polymer (FRP), fabric-reinforced cementitious matrix (FRCM), and steel jacketing. The comparative performance of these methods is assessed based on effectiveness, cost–benefit considerations, service life extension, and practical implement ability. The review highlights that no single mitigation strategy is universally optimal; instead, integrated approaches combining multiple techniques provide the most effective long-term protection. Key research gaps are identified in the areas of long-term performance monitoring, internal corrosion detection, and durability modeling under combined environmental actions. The findings of this study provide valuable insights for the design, maintenance, and rehabilitation of CFST structures, contributing to the development of more durable and sustainable infrastructure systems. Full article

The structural performance of reinforced concrete (RC) columns can be substantially improved by using advanced confinement systems and sustainable cementitious materials. This study presents an integrated experimental, numerical, and analytical investigation of RC columns strengthened with self-compacting geopolymer concrete (SCGC) and carbon fiber-reinforced polymer (CFRP) under axial compression. Twelve column specimens were tested across four groups: conventional RC columns, unconfined SCGC columns, SCGC-jacketed columns (CONF. SCGC), and CFRP-wrapped columns (CONF. FRP), in three cross-sectional geometries: square (177 × 177 mm), rectangular (265 × 177 mm), and circular (Ø200 mm). Experimental results demonstrated that replacing conventional concrete with SCGC improved deformation capacity, increasing the ultimate axial displacement from 2.07 mm in the reference square RC column (RC C1) to 3.21 mm in the corresponding square SCGC specimen (SCGC C1). On a normalized stress basis, the unconfined SCGC specimens achieved ultimate axial stress values of 56–64 MPa compared to 41–49 MPa for the RC reference columns of the same geometry, representing material-level strength gains of 1.30–1.49×. The application of external confinement further enhanced column behaviour. The CFRP-wrapped specimens achieved the highest material-level strength efficiency, with normalized ultimate axial stress values of 98–108 MPa for the square and rectangular geometries, representing gains of 2.01–2.41× over the corresponding unconfined RC columns of identical cross-section. The SCGC-jacketed specimens achieved the highest absolute load capacities, with CONF. SCGC C2 reaching 8270 kN and a maximum stiffness of 5531 kN/mm and energy absorption of 19,740 kN·mm. However, on a normalized stress basis, the SCGC-jacketed square and rectangular specimens achieved 45–47 MPa, comparable to the RC reference columns, confirming that their absolute load gains are primarily attributable to section enlargement rather than intrinsic material strength enhancement. The circular SCGC-jacketed specimen achieved a normalized stress of 43 MPa, consistent with the same trend. A three-dimensional nonlinear finite element model developed in ABAQUS using the Concrete Damaged Plasticity model and cohesive zone interactions showed close agreement with experimental results, with mean prediction ratios of 1.03 for ultimate load and 0.96 for displacement. An analytical model provided conservative estimates of axial capacity. The findings demonstrate that CFRP wrapping offers superior material-level confinement efficiency, while SCGC jacketing provides the highest absolute load capacity through combined section enlargement and passive confinement, representing a potentially more environmentally friendly strengthening strategy for existing RC columns. Full article

This study presents a comprehensive analysis and predictive modeling framework for the axial compressive strength (f_cc) and ultimate axial strain (ε_cu) of concrete columns confined within fiber-reinforced polymer (FRP) systems. Large databases comprising 3312 samples for f_cc and 3319 for ε_cu were compiled from the literature, encompassing a wide range of key variables, including unconfined concrete strength from 7 MPa to 204 MPa and diverse FRP confinement configurations. The datasets were subjected to extensive statistical and multivariate analyses to identify the primary factors influencing axial behavior and guide feature selection for predictive modeling. Three groups of machine learning (ML) algorithms were subsequently considered: (i) artificial neural networks (including multilayer perceptrons with one and two hidden layers), (ii) kernel-based models (Gaussian process regression and support vector regression), and (iii) tree-based ensemble models (gradient boosting machine, eXtreme gradient boosting, and light gradient boosting machine). Hyperparameters were optimized using grid search cross-validation, while feature importance analyses were performed to quantify the contribution of each input variable. Among all ML models, eXtreme gradient boosting demonstrated superior predictive performance, effectively capturing the nonlinear and multivariate interactions governing confinement effectiveness. Comparative analysis with the top performing regression-based formulations further highlighted the accuracy, robustness, and generalization capability of the eXtreme gradient boosting model. The findings provide a data-driven and interpretable framework for the design and prediction of FRP-confined concrete columns. Full article

This study presents a comparative evaluation of three machine learning models, XGBoost, AdaBoost, and LightGBM, for predicting the time-dependent bond strength between fiber-reinforced polymer (FRP) and timber in both normal and harsh environments. A dataset was compiled (79 for normal conditions and 265 for harsh environments) incorporating material properties, geometric parameters, exposure time, and solution pH as input features. Hyperparameter optimization was performed for each model, and performance was evaluated using R², RMSE, MAE, and MSE metrics. SHAP analysis and Partial Dependence Plots were employed to interpret feature importance and model behavior. Under normal conditions, XGBoost achieved the highest predictive accuracy (testing R² = 0.944, RMSE = 2.170, and MAE = 1.775), outperforming AdaBoost and LightGBM. However, in harsh environments, LightGBM demonstrated superior generalization, with the highest testing R² of 0.797 and the lowest RMSE of 0.549 and MAE of 0.431, outperforming XGBoost and AdaBoost. AdaBoost exhibited severe overfitting under harsh conditions, with a training-to-testing R² drop of 0.341. Feature importance analysis by SHAP analysis identified fiber tensile strength and exposure time as the most influential parameters governing bond performance. SHAP force plots demonstrated that fiber properties predominantly enhance bond strength, while pH consistently acts as a decreasing factor under harsh conditions. This research provides a robust predictive framework for FRP–timber bond durability, offering valuable insights for structural design and service life prediction in harsh environments. Full article

This study includes an interpretable machine learning (ML) framework for predicting the shear contribution of externally bonded fiber-reinforced polymer (FRP) composites in reinforced concrete beams. A database including total 313 experimental specimens was collected from previous experimental research. The data screening process has been conducted using the Isolation Forest algorithm, resulting in 268 cleaned specimens. The cleaned database was divided into a training subset containing 214 specimens and an independent test set containing 54 specimens. The trained subset was enlarged into 5204 synthetic data using two advanced generative models including Wasserstein generative adversarial network and conditional Variational autoencoder (CVAE). Separate constrained monotonic neural network (CMNN) models were then trained on both datasets and WGAN-based CMNN achieved $R^2=0.9524$ for the synthetic training dataset and $R^2=0.9120$ for the independent test set, whereas the CVAE-based CMNN achieved corresponding values of 0.9632 and 0.9011. To improve practical applicability, response functions were extracted from WGAN-based CMNN and fitted with analytical expressions to derive a closed-form prediction equation. The proposed equation was independently validated using separate unseen test specimens, which were not used in CMNN training and achieved R² $=$ 0.79, RMSE $=$ 24.98 kN, MAE $=$ 19.65 kN, MAPE $=$ 21.72%, VAF $=$ 79.35%, U95 $=$ ±54.94 kN, SI $=$ 3.04, and PI $=$ 0.11. Compared with ACI 440.2R-17, CSA-S806.12, CNR-DT200 R1.2013, TR-55, and JSCE, the proposed equation showed superior accuracy while maintaining a transparent and design-oriented format. Full article

The seismic assessment of existing strategic and highly occupied reinforced concrete buildings, such as schools located in moderate-to-high seismic regions, is a critical task, especially because they have been constructed in periods lacking performance-based seismic design requirements. Following a review of possible local and global structural strengthening strategies, this study presents the seismic evaluation and retrofit design of an existing reinforced concrete school building designed before the introduction of modern seismic codes. The assessment is supported by an in situ investigation campaign including destructive and non-destructive materials testing, geotechnical investigations, and a detailed survey of the original construction details. A three-dimensional numerical model, calibrated on the in situ survey and material test results, enables the evaluation of the building’s seismic performance in both the pre- and post-intervention configurations. The model also supports the optimization of retrofit costs: a constraint of relevance because the intervention was funded through a dedicated public budget allocated by the national authority and subject to public validation. This represents a procurement framework that explicitly links the achievable retrofit performance level to a fixed cost ceiling, unlike standard practice in most seismic-prone countries. A global strengthening strategy was implemented including new reinforced concrete shear walls structurally connected to the foundations of the existing walls, whose capacity was enhanced through the installation of micropiles. Fiber-reinforced polymer (FRP) wrapping was applied to improve both flexural and shear beam capacity, while steel jacketing was adopted for some vertical elements. The combined interventions significantly improved the seismic performance of the building, ensuring a safer and more reliable response under future seismic events, respecting the initial publicly available budget. Full article

Externally bonded reinforcement (EBR) using fiber reinforced polymer (FRP) is one of the most widely used techniques for strengthening reinforced concrete (RC) structures. However, early debonding of the concrete surface layer in the EBR method limits its structural performance. Recently, the externally bonded reinforcement on grooves (EBROG) method has emerged as a promising alternative. This study experimentally investigates the bond behavior between CFRP plates and concrete strengthened using the EBROG method. A total of 78 specimens were fabricated and evaluated using single-lap shear tests. The investigated parameters include groove dimensions, number of grooves, and concrete compressive strength. A digital image correlation (DIC) system was used to measure displacement. Unlike the EBR method, no debonding of the concrete surface layer occurred in the EBROG specimens, and the bond strength improved by 49.56–154.48% without additional surface treatment. Increased groove dimensions and a greater number of grooves significantly enhanced the bond performance. Higher concrete compressive strength and larger groove dimensions also delayed the onset of debonding. Based on the experimental results, a new effective strain model was proposed, and flexural capacity predictions using this model showed higher accuracy than those obtained from existing models. Full article

Existing analytical models for Fiber-Reinforced Polymer (FRP)-strengthened timber beams are generally limited to individual strengthening techniques and cannot readily accommodate hybrid reinforcement systems. This study develops a generalized analytical model to predict the flexural capacity of timber beams strengthened with near-surface-mounted (NSM) FRP bars, externally bonded FRP sheets, or their hybrid combination within a unified theoretical framework. The model is formulated based on internal force equilibrium and strain compatibility, incorporating a constitutive model for timber with linear elastic tensile behavior and a bilinear compressive stress–strain relationship including post-peak softening. The generalized formulation can be readily adapted to different strengthening configurations through appropriate simplifications. The proposed model was validated against experimental results obtained from four-point bending tests on small-scale timber beams strengthened with NSM GFRP bars and externally bonded GFRP sheets. The analytical predictions showed good agreement with the experimental results, with differences generally ranging from 2% to 23%, demonstrating satisfactory predictive accuracy. The experimental results further showed that the hybrid strengthening system increased the flexural capacity of the timber beams by up to 84% compared with the unstrengthened control beams, while also improving stiffness, ductility, and overall structural response. Failure was primarily due to timber tensile rupture and longitudinal splitting, whereas the GFRP reinforcement remained effective without rupture, indicating efficient utilization of the strengthening system. The proposed generalized analytical model provides a practical and reliable design tool for predicting the flexural strength of timber beams strengthened with various FRP reinforcement configurations, thereby supporting the structural rehabilitation and sustainable retrofitting of timber structures. Full article

Reinforced concrete beams with a fiber-reinforced polymer (FRP) plate bonded to their soffit, known as FRP-plated RC beams, commonly fail due to premature debonding of the FRP plate, limiting the utilization of the FRP strength. Inclined U-jacketing has been demonstrated to be effective as the end anchorage for mitigating debonding failures. The mechanism by which the inclined U-jacketing mitigates debonding failure remains unclear, and no design approach has been developed. Therefore, the present study has been conducted to investigate the mitigating effects of the key parameters of the inclined U-jacket through a series of four-point bending tests and systematic modeling. The test results indicate that both the inclination angle and the chamfer radius significantly affected the bond behavior of inclined U-jacket-to-concrete joints. Compared with the 45° configuration, reducing the inclination angle to 30° increased the peak load and peak displacement by 85.4% and 81.6%, respectively. In contrast, the effect of U-jacket side height became negligible once an effective bonded height had been reached, as increasing the side height from 75 mm to 120 mm changed the peak load by only 2.17%. In addition, a pre-peak parameter identification framework based on a power-function-type cohesive element constitutive relationship was proposed and validated. By analyzing the power-function parameters, namely the coefficient a and exponent b, the influences of U-jacket geometric variables on interfacial mechanical behavior were quantitatively characterized. The proposed approach provides experimentally verifiable parameterization to support the optimized design of inclined U-jacket anchorage systems. Full article

This study investigates hybrid fiber-reinforced polymer (FRP)–steel-reinforced concrete (RC) beams by using three-dimensional finite element models. The research systematically analyzes the influence of key parameters, including FRP type, FRP bar ratio (ρ_f), the ratio of FRP to total reinforcement (ρ_f/ρ_t), and concrete strength. The load–deflection response of the hybrid RC beams is analyzed in detail. The results show that the investigated parameters have a relatively limited influence on the cracking moment, but significantly affect both the yield and ultimate moments. When ρ_f/ρ_t increases from 0 to 0.75, the yield moment decreases by up to 44.34%. When ρ_f increases from 0.55% to 0.88%, the yield moment increases by 50.63%. Meanwhile, increasing the concrete strength significantly enhances the ultimate moment, with a maximum increase of 38.46%. In addition, an energy ductility index is adopted to quantitatively evaluate the structural ductility. The results indicate that the energy ductility index is consistently lower than the conventional ductility index. Finally, to improve the accuracy of theoretical predictions, a semi-empirical simplified formula is proposed for estimating the FRP bar stress at the ultimate state of hybrid beams. The verification results show that the proposed prediction method agrees well with the experimental data, demonstrating that the simplified formula has good applicability and reliability within the parameter range investigated in this study. Full article

The performance of steel structures can decrease over time due to several factors and therefore requires serious consideration to avoid any risks to users. Currently, strengthening of structures using fiber-reinforced polymer (FRP) materials is gaining in popularity. This paper presents a finite element (FE) analysis to investigate the flexural performance of steel I-beams strengthened with unbonded carbon FRP (CFRP). A total of 38 beam models is developed with four influential parameters considered, namely CFRP thickness, CFRP elastic modulus, type of steel beam cross-section, and strengthening length. The results of the investigation confirm that unbonded CFRP strengthening improves the performance of steel I-beams. Initial stiffness and moment capacity of the beams increase as the thickness of CFRP, CFRP elastic modulus, and strengthening length increase. The increase in the initial stiffness of beams tends to be linear as the length of strengthening increases. Meanwhile, the linear trend occurs only up to CFRP lengths of 700 mm or 800 mm for the increase in beam moment capacity. Unbonded CFRP strengthening contributes higher to steel beams with a lower moment of inertia. Full article

Reinforced concrete (RC) beams are crucial load-bearing members in multistory buildings. Due to architectural modifications, increased service loads, or construction deficiencies, these members often require flexural strengthening to restore or enhance their performance. The use of prefabricated reinforced ultra-high-performance fiber-reinforced concrete (UHPFRC) plates has recently emerged as a promising strengthening technique. When attached to the tension, compression, or both faces of RC beams, these plates provide noteworthy structural benefits. This study presents a detailed investigation—using nonlinear calibrated finite element (FE) models—into the flexural strengthening of RC beams using reinforced UHPFRC plates. A total of 18 large-scale RC beams were explored, including two control specimens and 16 strengthened beams. The control specimens comprised one beam with a tensile steel ratio close to the minimum code thresholds and another with a conventional reinforcement ratio typical of standard design. The strengthening schemes were developed to enhance the flexural capacity of the first control beam to a level comparable to the ideal reference specimen. A simplified analytical tool was developed to estimate the peak load of control and strengthened specimens for the design of upgrading schemes. The parametric study in the FE matrix examined the effects of reinforcement type within the UHPFRC plates (steel or glass fiber-reinforced-polymer (GFRP) bars), plate location (tension side, compression side, or both), bonding method (adhesive, mechanical, or combined), and end anchorage condition (with or without fiber-reinforced polymer (FRP) U-wraps). The beams’ behavior was evaluated in terms of load-deflection response, stiffness, and failure mode. The results demonstrated that combined adhesive–mechanical bonding with compression-side UHPFRC plates provided the most efficient and reliable strengthening technique. Full article

Timber is a natural and renewable construction material, so it is environmentally friendly. However, timber has natural defects and also deteriorates over time. These problems require structural reinforcement. The present study aims to systematically explore the compression performance of natural Larch circular columns reinforced with Carbon Fiber-Reinforced Polymer (CFRP) and Basalt Fiber-Reinforced Polymer (BFRP). Thirty specimens were tested in pure axial compression to investigate the influence of the number of wrapping layers (0–3 layers), the specimen height (150, 200 and 300 mm) and the type of FRP material. The strengthening mechanism primarily relies on the passive hoop confinement provided by the FRP, which restricts the transverse expansion of the timber under axial load. Because CFRP possesses a higher tensile strength and elastic modulus than BFRP, it activates confining stresses more rapidly and provides a stronger restraint, leading to distinct improvements in load-bearing performance. The experimental results show that the failure mode of the short columns changes from inherent brittle splitting to a more ductile failure pattern, characterized by FRP ruptures and crushing of the timber as a result of external FRP wrapping. The axial compressive performance of the timber columns has been improved with both FRP materials. Given the same conditions, the CFRP caused increases in load-bearing capacity and stiffness, as a result of its higher tensile strength and elastic modulus, which gave rise to peak loads that were 4.9% to 7.8% greater than the BFRP-strengthened groups. There was a tendency for the reinforcement efficiency to increase with the number of layers of CFRP wrapping, and 2–3 layers of CFRP was found to be the optimal number of layers based on the aspect of material efficiency. In addition, FRP confinement was able to prevent premature failure and improve the ultimate transverse strain by as much as 2.1 times, significantly increasing ductility and energy dissipation. Finally, a theoretical ultimate strength prediction model was developed based on the passive confinement theory with the introduction of a height correction factor to consider the slenderness effects. The proposed model showed an overall coefficient of determination R² of 0.8027, which was good for reference for designing the reinforcement and evaluation of the performance of sustainable timber structure. Full article

Externally bonded fiber-reinforced polymer (EB-FRP) systems have been extensively investigated for tension strengthening concrete structures. Interpretation of the available evidence remains challenging because experimental methods, specimen scales, material systems, anchorage configurations, and reporting practices vary substantially across the literature. This systematic review synthesized 174 peer-reviewed studies published between 1994 and 2026, comprising 3908 experimental test results and 42 analytical formulations addressing unanchored and anchored EB-FRP systems. Review findings showed that bond performance in unanchored systems is governed primarily by FRP stiffness, bond geometry, concrete properties, adhesive behavior, surface preparation, and environmental exposure. These parameters influence bond capacity, debonding strain, effective bond length, and failure mode. Anchored configurations consistently enhanced force transfer, delayed premature debonding, and improved load-carrying capacity relative to unanchored systems. Unanchored systems dominated the available evidence base with 3162 test results, whereas only 96 multi-anchor system tests were identified, highlighting limited understanding of anchor interaction and load redistribution mechanisms. CFRP represented the dominant material system, while substantially fewer studies investigated GFRP, BFRP, and AFRP systems. Existing strength models generally captured specific failure mechanisms within their calibration ranges but demonstrated limited transferability across different geometries, loading conditions, anchorage configurations, and environmental conditions. Limited evidence remains available for scale transfer, durability degradation, anchor strip interaction, and multi-anchor load sharing under field-representative conditions. Future research should focus on standardized benchmarking procedures, large-scale validation programs, durability-informed design approaches, experimentally validated numerical modeling, and unified design provisions for EB-FRP strengthening systems. Full article