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Highlights • A review on torsional strengthening of RC beams with EB composites was provided. • A database of RC beams strengthened in torsion with EB FRP and FRCM was developed. • Data distribution, wrapping methods, failure modes, anchorage systems were evaluated. • The accuracy of existing analytical and numerical models was compared. • Design provisions for torsional strengthening with EB FRP composites were evaluated. Abstract The use of externally bonded (EB) fiber reinforced composites to strengthen reinforced concrete (RC) structures has been explored extensively in recent decades. While many studies have been conducted on the flexural, shear, and axial strengthening of RC members, far fewer studies have been conducted on torsional strengthening. Thus, the knowledge on the behavior of RC members strengthened in torsion with EB composites is rather limited. The aim of this paper was to present a comprehensive review and evaluation of torsional strengthening of RC beams using EB composites. A detailed survey of the literature was conducted, and a database of experimental tests was developed. The database includes beams reinforced with EB fiber reinforced polymer (FRP) and EB fiber reinforced cementitious matrix (FRCM) composites. The effectiveness of the strengthening system was examined in terms of geometrical and mechanical characteristics of the RC beam, composite type, and composite wrapping configuration. Different modes of failure of the strengthened beams were also discussed. Additionally, analytical and numerical methods developed to predict the torsional response of RC beams strengthened with EB composites were summarized and discussed. Finally, design provisions were examined based on the knowledge gained from this study. [ABSTRACT FROM AUTHOR]

Repair and rehabilitation of reinforced concrete (RC) structures with different types of external reinforcement has been investigated widely. Fiber reinforced cementitious matrix (FRCM) is a new type of composite system that contains continuous fibers embedded in inorganic matrix. This system has been proven to be effective for strengthening RC members under flexure, shear, and axial loadings. However, studies on the use of FRCM composite for torsional strengthening are very limited. This study investigated experimentally the torsional behavior of solid rectangular RC beams strengthened with externally bonded PBO-FRCM composite in different wrapping configurations. The study focused on the effect of fiber orientation as well as other parameters that influence the torsional strength, torsional moment-twist per unit length response, and mode of failure including fiber continuity and number of composite layers. The strains in the internal and external reinforcement and the longitudinal elongation of the strengthened beams were examined, and a comparison with other types of fiber reinforced composite was also discussed. The 90° fiber orientation (perpendicular to the beam longitudinal axis) was more effective in increasing the torsional strength than the 45° fiber orientation since premature debonding of the fibers occurred at the ends of the 45° strips, which contrasted the potential benefits from optimizing the fiber orientation and led to the underutilization of the composite. The 90° fiber orientation was also more effective than the 0° fiber orientation. [ABSTRACT FROM AUTHOR]

Fiber Reinforced Cementitious Matrix (FRCM) composites can be employed as a valid alternative to Fiber Reinforced Polymers (FRP) composites for strengthening existing reinforced concrete (RC) structures. The weakness of FRCM-concrete joints has been reported to be at the matrix–fiber interface rather than within the concrete substrate, as is usually reported in the case of FRP-concrete joints. The experimental investigations regarding FRCM strengthening available in the literature have been performed by applying the FRCM composite onto a surface that was treated before the application, usually by grinding or sandblasting. However, the role of the substrate characteristics on the failure mechanism of the FRCM composite has not been properly investigated. This paper presents the experimental results obtained from FRCM-concrete joints tested using single-lap direct-shear tests. FRCM composites with different bonded lengths and bonded widths were applied onto concrete specimens with different surface preparations and different concrete strengths. The influence of shrinkage cracks and load distribution along the composite width on the failure modes observed is discussed. In order to avoid the possibility of sudden composite detachment failure, the authors recommend that the substrate surface should be treated, and the matrix shrinkage should be controlled. [ABSTRACT FROM AUTHOR]

A technique to repair reinforced concrete (RC) bridge columns containing interlocking spirals and having buckled and/or fractured longitudinal bars was assessed through experimental tests. The repair technique involved removing spirals, removing longitudinal bar segments in the plastic hinge region and replacing them with new bar segments that were mechanically spliced to the existing bars with bar couplers, and applying an externally bonded carbon fiber reinforced polymer (CFRP) jacket in lieu of replacing the spirals. Two 1/2-scale prototype bridge columns repaired using two types of mechanical couplers were investigated in this study. The repaired columns were tested under constant axial loading and slow reversed cyclic lateral loading resulting in combined flexural moment, shear, and torsional moment. Test results show that the repair method was successful in restoring the lateral and torsional strength to both columns. The lateral and torsional deformation capacity was restored to one column, while the other was not able to be assessed due to early termination of testing. This study also provides information on the performance of mechanical bar couplers in plastic hinge regions. [ABSTRACT FROM AUTHOR]

This paper presents an experimental and analytical investigation on the compressive performance of concrete cylinders internally reinforced with steel-fiber-reinforced composite bars (SFCBs) and externally confined with fiber-reinforced polymer (FRP) sheets, termed herein as S-F-RC cylinders. Eleven concrete cylinders, with different confinement conditions and with (or without) longitudinal SFCBs, were tested under monotonic compression. Two distinguishable failure mechanisms, global buckling and local buckling, were discovered for SFCBs in S-F-RC cylinders, under weak and strong confinement conditions, respectively. The S-F-RC cylinders exhibited a marked increase in failure strain of the confinement, directly translating to an enhanced compressive failure strain for the longitudinal SFCBs under strong confinement conditions. Existing models for FRP-reinforced concrete cylinders were found to underestimate the load-carrying capacity of S-F-RC cylinders. An existing compressive stress-strain model for SFCB was extended to the case of S-F-RC cylinders. The proposed method offers accurate predictions, effectively mitigating the discrepancies caused by varying confinement and material properties across different SFCBs. • Compressive performance of FRP-confined SFCB-reinforced concrete is presented. • Different buckling failure mode observed for SFCB under weak or strong confinement. • Model is developed for axial compressive strength of SFCB in FRP-confined concrete. [ABSTRACT FROM AUTHOR]

• Established a database with 442 RC beams strengthened in shear with FRP and reduced the scale to 315 specimens by an unsupervised anomaly detection algorithm. • Developed six machine learning models and substantially outperformed the six traditional analytical equations in prediction accuracy. • Proposed an explicit and practical equation to predict the shear strength contribution of FRP based on the machine learning models, which showed high prediction accuracy. This study identified the factors affecting the contribution of externally bonded fiber reinforced polymer (FRP) composite (V f) to the shear strength of reinforced concrete (RC) beams with internal shear reinforcement through the use of interpretable machine learning (ML). A comprehensive database with 442 RC beams strengthened in shear with FRP was established and subjected to data anomaly detection using the isolation forest algorithm. Six ML models (artificial neural networks (ANN), XGBoost, random forest, CatBoost, LightGBM, AdaBoost algorithms) were trained to predict V f. The ML models outperform six traditional explicit equations commonly used in design codes or the literature in terms of accuracy and variation. Based on the interpretable ML, the important variables were revealed; in particular the effective height of FRP, shear span ratio, and reinforcement method (U-wrap, full wrapping, side bonding) had significant influence on V f. Finally, driven by results of the ML models, an explicit equation was derived to predict V f , considering the physical meaning of the key influencing parameters. This study combines ML models and traditional physical models to achieve a novel, interpretable ML method to predict V f. [ABSTRACT FROM AUTHOR]

• The spike anchors enabled full utilization of the SRP material strength. • FDM approach can accurately predict the full-range behavior of anchored specimens. • Anchored specimens exhibited a three-stage load response. Steel reinforced polymer (SRP) composite has recently emerged as an effective and economical solution for strengthening of reinforced concrete (RC) structures. Premature debonding failure of unanchored SRP at low load levels generally governs the performance of RC structures strengthened with externally bonded SRP. Therefore, a novel yet simple spike-shaped anchorage system was proposed in this study to prevent the debonding failure of SRP and to improve the interfacial shear capacity. Experimental investigation through single-lap shear tests of SRP-concrete joints showed that the anchorage system changed the failure mode from composite debonding to fiber rupture. In addition, the anchorage system substantially increased the peak load and reduced the interfacial slippage of the SRP-concrete joint compared to the unanchored condition. A numerical procedure based on the finite difference method was developed to predict the full-range load response, and results matched well with the full-range experimental responses of anchored and unanchored specimens. Parametric study of the test results and numerical simulation based on finite difference method both showed that the fiber rupture failure mode could be achieved for anchors in various positions along the bonded length. The closer the anchor is to the loaded end, the less global slip was obtained when the load reached the peak value. [ABSTRACT FROM AUTHOR]

A ground-coupled ground penetrating radar (GPR) system was used to assess the condition of two reinforced concrete bridge decks. After each GPR assessment was completed, the bridge deck was rehabilitated using a hydrodemolition process to remove deteriorated concrete from upper surface of the deck. LiDAR technology was used to create maps depicting the deck surface before and after the concrete removal. The objective of this work was to corroborate the GPR condition assessments by comparing the spatial distribution of the GPR and LiDAR mappings. This work illustrates that GPR data have the potential to predict concrete repair estimates. [ABSTRACT FROM AUTHOR]

Ground penetrating radar (GPR) is an electromagnetic-based nondestructive geophysical tool that is widely used for pavement investigations, including the differentiation of pavement layers, the mapping of layer thicknesses, and the assessment of pavement condition. This paper presents a case study in which an air-launched GPR system consisting of two truck-mounted GSSI antennae driven at near-highway speeds was used to investigate two segments of asphalt paved roadway in central Missouri. The acquired data were interpreted; pavement layers were differentiated, the variable thicknesses of the pavement layers were mapped, bulk pavement condition were assessed, and optimum acquisition and processing parameters were developed. Core control, visual assessments, and limited ground-coupled GPR data were used to constrain and verify the reliability of the interpretations of the acquired air-launched GPR data. [ABSTRACT FROM AUTHOR]