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22 pages, 8482 KiB  
Article
Effect of C-FRP (Carbon Fiber Reinforced Polymer) Rope and Sheet Strengthening on the Shear Behavior of RC Beam-Column Joints
by Emmanouil Golias and Chris Karayannis
Fibers 2025, 13(9), 113; https://doi.org/10.3390/fib13090113 - 22 Aug 2025
Abstract
This study presents a high-performance external strengthening strategy for reinforced concrete (RC) beam–column joints, integrating near-surface mounted (NSM) Carbon Fiber Reinforced Polymer (C-FRP) ropes with externally bonded C-FRP sheets. The X-shaped ropes, anchored diagonally on both principal joint faces and complemented by vertical [...] Read more.
This study presents a high-performance external strengthening strategy for reinforced concrete (RC) beam–column joints, integrating near-surface mounted (NSM) Carbon Fiber Reinforced Polymer (C-FRP) ropes with externally bonded C-FRP sheets. The X-shaped ropes, anchored diagonally on both principal joint faces and complemented by vertical ropes at column corners, provide enhanced core confinement and shear reinforcement. C-FRP sheets applied to the beam’s plastic hinge region further increase flexural strength and delay localized failure. Three full-scale, shear-deficient RC joints were subjected to cyclic lateral loading. The unstrengthened specimen (JB0V) exhibited rapid stiffness deterioration, premature joint shear cracking, and unstable hysteretic behavior. In contrast, the specimen strengthened solely with X-shaped C-FRP ropes (JB0VF2X2c) displayed a markedly slower rate of stiffness degradation, delayed crack development, and improved energy dissipation stability. The fully retrofitted specimen (JB0VF2X2c + C-FRP) demonstrated the most pronounced gains, with peak load capacity increased by 65%, equivalent viscous damping enhanced by 55%, and joint shear deformations reduced by more than 40%. Even at 4% drift, it retained over 90% of its peak strength, while localizing damage away from the joint core—a performance unattainable by the unstrengthened configuration. These results clearly establish that the combined C-FRP rope–sheet system transforms the seismic response of deficient RC joints, offering a lightweight, non-invasive, and rapidly deployable retrofit solution. By simultaneously boosting shear resistance, ductility, and energy dissipation while controlling damage localization, the technique provides a robust pathway to extend service life and significantly enhance post-earthquake functionality in critical structural connections. Full article
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45 pages, 770 KiB  
Review
Neural Correlates of Burnout Syndrome Based on Electroencephalography (EEG)—A Mechanistic Review and Discussion of Burnout Syndrome Cognitive Bias Theory
by James Chmiel and Agnieszka Malinowska
J. Clin. Med. 2025, 14(15), 5357; https://doi.org/10.3390/jcm14155357 - 29 Jul 2025
Viewed by 708
Abstract
Introduction: Burnout syndrome, long described as an “occupational phenomenon”, now affects 15–20% of the general workforce and more than 50% of clinicians, teachers, social-care staff and first responders. Its precise nosological standing remains disputed. We conducted a mechanistic review of electroencephalography (EEG) studies [...] Read more.
Introduction: Burnout syndrome, long described as an “occupational phenomenon”, now affects 15–20% of the general workforce and more than 50% of clinicians, teachers, social-care staff and first responders. Its precise nosological standing remains disputed. We conducted a mechanistic review of electroencephalography (EEG) studies to determine whether burnout is accompanied by reproducible brain-function alterations that justify disease-level classification. Methods: Following PRISMA-adapted guidelines, two independent reviewers searched PubMed/MEDLINE, Scopus, Google Scholar, Cochrane Library and reference lists (January 1980–May 2025) using combinations of “burnout,” “EEG”, “electroencephalography” and “event-related potential.” Only English-language clinical investigations were eligible. Eighteen studies (n = 2194 participants) met the inclusion criteria. Data were synthesised across three domains: resting-state spectra/connectivity, event-related potentials (ERPs) and longitudinal change. Results: Resting EEG consistently showed (i) a 0.4–0.6 Hz slowing of individual-alpha frequency, (ii) 20–35% global alpha-power reduction and (iii) fragmentation of high-alpha (11–13 Hz) fronto-parietal coherence, with stage- and sex-dependent modulation. ERP paradigms revealed a distinctive “alarm-heavy/evaluation-poor” profile; enlarged N2 and ERN components signalled hyper-reactive conflict and error detection, whereas P3b, Pe, reward-P3 and late CNV amplitudes were attenuated by 25–50%, indicating depleted evaluative and preparatory resources. Feedback processing showed intact or heightened FRN but blunted FRP, and affective tasks demonstrated threat-biassed P3a latency shifts alongside dampened VPP/EPN to positive cues. These alterations persisted in longitudinal cohorts yet normalised after recovery, supporting trait-plus-state dynamics. The electrophysiological fingerprint differed from major depression (no frontal-alpha asymmetry, opposite connectivity pattern). Conclusions: Across paradigms, burnout exhibits a coherent neurophysiological signature comparable in magnitude to established psychiatric disorders, refuting its current classification as a non-disease. Objective EEG markers can complement symptom scales for earlier diagnosis, treatment monitoring and public-health surveillance. Recognising burnout as a clinical disorder—and funding prevention and care accordingly—is medically justified and economically imperative. Full article
(This article belongs to the Special Issue Innovations in Neurorehabilitation)
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16 pages, 5084 KiB  
Article
Novel Ductile Moment-Resisting Frame Compound of Steel Gusset Plate for Beam-to-Column Connections and I-Shaped FRP Profile Sections
by Ali Ghamari, Chanachai Thongchom, Adamantis G. Zapris and Violetta K. Kytinou
J. Compos. Sci. 2025, 9(6), 280; https://doi.org/10.3390/jcs9060280 - 30 May 2025
Viewed by 565
Abstract
Moment-resisting frames (MRFs) are characterized by high energy dissipation capacity relying on plastic hinge formation at the two ends of beams. Despite their numerous advantages, Fiber-Reinforced Polymer (FRP) profile sections used in MRF systems suffer from low ductility, which remains a dilemma. FRP [...] Read more.
Moment-resisting frames (MRFs) are characterized by high energy dissipation capacity relying on plastic hinge formation at the two ends of beams. Despite their numerous advantages, Fiber-Reinforced Polymer (FRP) profile sections used in MRF systems suffer from low ductility, which remains a dilemma. FRP profiles have emerged as a novel and valuable material with significant advancement in structural engineering. In this paper, an MRF system composed of novel gusset plate steel connections (to provide ductility) and FRP profile sections for beams and columns is proposed and investigated numerically and parametrically. The results indicate that up to a rotation of 0.04 rad, the proposed gusset plate dissipates energy, whereas the beam and columns remain essentially elastic. Accordingly, with an increase in the ratio of vertical length to thickness of the gusset plate, energy dissipation is reduced. Through an increase in the ratio of horizontal length to thickness of the gusset plate from 63.5 to 127 and 254, the ultimate strength of the connection is reduced by 4% to 10% and 3% to 7%, respectively. It is suggested that gusset plate thickness be selected in such a way that its slenderness is not less than 47. Subsequently, the required equation is proposed to achieve the optimum performance of the system. Full article
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35 pages, 13152 KiB  
Article
Prediction of Member Forces of Steel Tubes on the Basis of a Sensor System with the Use of AI
by Haiyu Li and Heungjin Chung
Sensors 2025, 25(3), 919; https://doi.org/10.3390/s25030919 - 3 Feb 2025
Cited by 1 | Viewed by 982
Abstract
The rapid development of AI (artificial intelligence), sensor technology, high-speed Internet, and cloud computing has demonstrated the potential of data-driven approaches in structural health monitoring (SHM) within the field of structural engineering. Algorithms based on machine learning (ML) models are capable of discerning [...] Read more.
The rapid development of AI (artificial intelligence), sensor technology, high-speed Internet, and cloud computing has demonstrated the potential of data-driven approaches in structural health monitoring (SHM) within the field of structural engineering. Algorithms based on machine learning (ML) models are capable of discerning intricate structural behavioral patterns from real-time data gathered by sensors, thereby offering solutions to engineering quandaries in structural mechanics and SHM. This study presents an innovative approach based on AI and a fiber-reinforced polymer (FRP) double-helix sensor system for the prediction of forces acting on steel tube members in offshore wind turbine support systems; this enables structural health monitoring of the support system. The steel tube as the transitional member and the FRP double helix-sensor system were initially modeled in three dimensions using ABAQUS finite element software. Subsequently, the data obtained from the finite element analysis (FEA) were inputted into a fully connected neural network (FCNN) model, with the objective of establishing a nonlinear mapping relationship between the inputs (strain) and the outputs (reaction force). In the FCNN model, the impact of the number of input variables on the model’s predictive performance is examined through cross-comparison of different combinations and positions of the six sets of input variables. And based on an evaluation of engineering costs and the number of strain sensors, a series of potential combinations of variables are identified for further optimization. Furthermore, the potential variable combinations were optimized using a convolutional neural network (CNN) model, resulting in optimal input variable combinations that achieved the accuracy level of more input variable combinations with fewer sensors. This not only improves the prediction performance of the model but also effectively controls the engineering cost. The model performance was evaluated using several metrics, including R2, MSE, MAE, and SMAPE. The results demonstrated that the CNN model exhibited notable advantages in terms of fitting accuracy and computational efficiency when confronted with a limited data set. To provide further support for practical applications, an interactive graphical user interface (GUI)-based sensor-coupled mechanical prediction system for steel tubes was developed. This system enables engineers to predict the member forces of steel tubes in real time, thereby enhancing the efficiency and accuracy of SHM for offshore wind turbine support systems. Full article
(This article belongs to the Section Sensors Development)
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16 pages, 2857 KiB  
Article
Fatigue Life Prediction of FRP-Strengthened Reinforced Concrete Beams Based on Soft Computing Techniques
by Zhimei Zhang and Xiaobo Wang
Materials 2025, 18(2), 230; https://doi.org/10.3390/ma18020230 - 7 Jan 2025
Cited by 1 | Viewed by 1100
Abstract
This paper establishes fatigue life prediction models using the soft computing method to address insufficient parameter consideration and limited computational accuracy in predicting the fatigue life of fiber-reinforced polymer (FRP) strengthened concrete beams. Five different input forms were proposed by collecting 117 sets [...] Read more.
This paper establishes fatigue life prediction models using the soft computing method to address insufficient parameter consideration and limited computational accuracy in predicting the fatigue life of fiber-reinforced polymer (FRP) strengthened concrete beams. Five different input forms were proposed by collecting 117 sets of fatigue test data of FRP-strengthened concrete beams from the existing literature and integrating the outcomes from Pearson correlation analysis and significance testing. Using Gene Expression Programming (GEP), the effects of various input configurations on the accuracy of model predictions were examined. The model prediction results were also evaluated using five statistical indicators. The GEP model used concrete compressive strength, the steel reinforcement stress range ratio to the yield strength, and the stiffness factor as input parameters. Subsequently, using the same input parameters, the Multi-Objective Genetic Algorithm Evolutionary Polynomial Regression (MOGA-EPR) method was then employed to develop a fatigue life prediction model. Sensitivity analyses of the GEP and MOGA-EPR models revealed that both could precisely capture the fundamental connections between fatigue life and multiple contributing variables. Compared to existing models, the proposed ones have higher prediction accuracy with a coefficient of determination reaching 0.8, significantly enhancing the accuracy of fatigue life predictions for FRP-strengthened concrete beams. Full article
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18 pages, 4714 KiB  
Article
Experimental Research on the Possibility of Changing the Adhesion of Epoxy Glue to Concrete
by Andrzej Szewczak and Grzegorz Łagód
Materials 2024, 17(22), 5398; https://doi.org/10.3390/ma17225398 - 5 Nov 2024
Cited by 1 | Viewed by 1043
Abstract
Among the many methods of joining different materials, gluing is characterized by its most specific nature. In comparison with, for example, welded, screwed, or overlapped connections, a glued connection depends on the largest number of factors. Many of them are related to the [...] Read more.
Among the many methods of joining different materials, gluing is characterized by its most specific nature. In comparison with, for example, welded, screwed, or overlapped connections, a glued connection depends on the largest number of factors. Many of them are related to the phenomenon of adhesion, which is complicated by definition. It has many shapes and forms, and its existence determines not only the durability of such a joint but also the possibility of its execution. Epoxy polymers are among the most commonly used adhesives. Their extremely good parameters can be easily modified by additives in the form of fillers. Compatibility between the filler and the adhesive allows for further improving the adhesive parameters in the glued joint. However, in order to effectively combine the adhesive and the filler, different, often specific mixing methods must be used. The following study presents the results obtained in an experimental research program, the aim of which was to increase the adhesion of epoxy resin to a properly prepared concrete substrate. As a method to increase the final adhesion, the addition of microsilica and carbon nanotubes in an experimentally determined amount was selected. The use of sonication as a mixing method together with cavitation allowed for improving the parameters which determine the final adhesion of the adhesive to concrete. The parameters which were selected to describe the course of changes in the adhesion of the adhesive to the concrete substrate were the viscosity, free surface energy, surface parameters, adhesion, and SEM images of the tested resin in various modification configurations. The obtained results make it possible to form stronger and more durable adhesive joints during the reinforcement of concrete structural elements using fiber-reinforced polymer (FRP) composites. Full article
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14 pages, 10874 KiB  
Article
Evaluating Pull-Out Behavior of Timber Connections: A Comparison of Dowelled Joints and Axially Loaded Screws
by Haksung Lee, Man-Kwon Choi, Bo-Seong Seo, Young-Seok Cho and Byung-Joo Kim
Buildings 2024, 14(11), 3369; https://doi.org/10.3390/buildings14113369 - 24 Oct 2024
Viewed by 1354
Abstract
This study examines the pull-out behavior of timber elements connected using dowelled joints (type 1) and axially loaded screws (type 2), focusing on numerical predictions and experimental validation under various conditions. Different screw diameters, configurations, material properties, and corrosion resistance are examined. Pull-out [...] Read more.
This study examines the pull-out behavior of timber elements connected using dowelled joints (type 1) and axially loaded screws (type 2), focusing on numerical predictions and experimental validation under various conditions. Different screw diameters, configurations, material properties, and corrosion resistance are examined. Pull-out tests demonstrated that type 2 connections, particularly using 10 mm and 14 mm screws, outperformed traditional dowelled joints in terms of load capacity. Numerical analysis based on Eurocode 5 showed close alignment with experimental results, particularly for screws with actual thread diameters of 5.2 mm and 6.2 mm, with minor deviations attributed to material variability. The finite volume method (FVM), implemented using the Geodict ElastoDict software, provided additional insights into the mechanical behavior of the connections. Corrosion resistance tests confirmed the long-term durability of fiber-reinforced polymer (FRP) components in saline environments, with negligible material degradation after 28 days of exposure. The 10-90-6 screw configuration was identified as the most efficient, balancing load capacity, displacement, and material cost. These findings highlight the effectiveness of both Eurocode 5 and FVM-based approaches for predicting screw behavior and emphasize the importance of accounting for material heterogeneity in timber connection design. Full article
(This article belongs to the Section Building Materials, and Repair & Renovation)
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39 pages, 31615 KiB  
Article
Seismic Retrofit Case Study of Shear-Critical RC Moment Frame T-Beams Strengthened with Full-Wrap FRP Anchored Strips in a High-Rise Building in Los Angeles
by Susana Anacleto-Lupianez, Luis Herrera, Scott F. Arnold, Winston Chai, Todd Erickson and Anne Lemnitzer
Appl. Sci. 2024, 14(19), 8654; https://doi.org/10.3390/app14198654 - 25 Sep 2024
Cited by 1 | Viewed by 1986
Abstract
This paper discusses the iteration of a seismic retrofit solution for shear-deficient end regions of 19 reinforced concrete (RC) moment-resisting frame (MRF) T-beams located in a 12-story RC MRF building in downtown Los Angeles, California. Local strengthening with externally bonded (EB) fiber-reinforced polymer [...] Read more.
This paper discusses the iteration of a seismic retrofit solution for shear-deficient end regions of 19 reinforced concrete (RC) moment-resisting frame (MRF) T-beams located in a 12-story RC MRF building in downtown Los Angeles, California. Local strengthening with externally bonded (EB) fiber-reinforced polymer (FRP) fabric was chosen as the preferred retrofit strategy due to its cost-effectiveness and proven performance. The FRP-shear-strengthening scheme for the deficient end-hinging regions of the MRF beams was designed and evaluated through large-scale cyclic testing of three replica specimens. The specimens were constructed at 4/5 scale and cantilever T-beam configurations with lengths of 3.40 m or 3.17 m. The cross-sectional geometry was 0.98 × 0.61 m with a top slab of 1.59 m in width and 0.12 m in thickness. Applied to these specimens were three different retrofit configurations, tested sequentially, namely: (a) unanchored continuous U-wrap; (b) anchored continuous U-wrap with conventional FRP-embedded anchors at the ends; and (c) fully closed external FRP hoops made of discrete FRP U-wrap strips and FRP through-anchors that penetrate the top slab and connect both ends of the FRP strips, combined with intermediate crack-control joints. The strengthening concept with FRP hoops precluded the premature debonding and anchor pullout issues of the two more conventional retrofit solutions and, despite a more challenging and labor-intensive installation, was selected for the in-situ implementation. The proposed hooplike EB-FRP shear-strengthening scheme enabled the deficient MRF beams to overcome a 30% shear overstress at the end-yielding region and to develop high-end rotations (e.g., 0.034 rad [3.4% drift] at peak and 0.038 rad [3.8% drift]) at strength loss for a beam that, otherwise, would have prematurely failed in shear. These values are about 30% larger than the ASCE 41 prescriptive value for the Life Safety (LS) performance objective. Energy dissipation achieved with the fully closed scheme was 108% higher than that of the unanchored FRP U-wrap and 45% higher than that of the FRP U-wrap with traditional embedded anchors. The intermediate saw-cut grooves successfully attracted crack formation between the strips and away from the FRP reinforcement, which contributed to not having any discernable debonding of the strips up to 3% drift. This paper presents the experimental evaluation of the three large-scale laboratory specimens that were used as the design basis for the final retrofit solution. Full article
(This article belongs to the Section Civil Engineering)
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19 pages, 13623 KiB  
Article
An Innovative Technique for the Strengthening of RC Columns and Their Connections with Beams Using C-FRP ROPES
by Chris Karayannis and Emmanuil Golias
Appl. Sci. 2024, 14(18), 8395; https://doi.org/10.3390/app14188395 - 18 Sep 2024
Cited by 6 | Viewed by 1689
Abstract
The application of the innovative C-FRP ropes for the strengthening of reinforced concrete columns is experimentally examined. Two real-scale specimens with the same geometrical characteristics and the same steel reinforcements were constructed for the needs of this investigation. The primary objective of the [...] Read more.
The application of the innovative C-FRP ropes for the strengthening of reinforced concrete columns is experimentally examined. Two real-scale specimens with the same geometrical characteristics and the same steel reinforcements were constructed for the needs of this investigation. The primary objective of the study is to investigate the efficacy of the use of C-FRP ropes as externally mounted reinforcement for the strengthening of deficient external columns. In this direction, (a) C-FRP ropes are applied as longitudinal reinforcement of the column for the increase in the flexural strength, (b) C-FRP ropes are applied as external confining stirrups in the critical end parts of the column for the improvement of the concrete strength and the development of local element ductility, and finally (c) C-FRP ropes are applied as external stirrups in the form of diagonal X-shaped reinforcement for the increase in the capacity of the part of the column connected with the beam (joint panel). Both specimens are tested under the same cyclic loading procedure that comprises seven steps and each step includes three full loading cycles. The maximum loads of the strengthened specimen at the three loading cycles of the seventh step were 40%, 72% and 87% higher than the corresponding ones of the unstrengthened specimen. On the other hand, the measured shear deformations of the joint panel of the pilot (unstrengthened) specimen at the sixth and the seventh steps were 43% and 44% higher than the corresponding ones of the strengthened specimen. In general, it is concluded that the strengthened column exhibited improved hysteretic response and the whole behavior was apparently improved compared to the pilot specimen without strengthening in terms of maximum loads per loading step, dissipated energy, and shear deformations of the joint panel. In particular, it is stressed that the measured shear deformations of the joint panel and strain gauge measurements have substantiated that the column and the connection panel of the strengthened specimen remain almost intact, whereas damage and eventually failure have been located in the column and the joint panel of the pilot specimen. Additionally, it is emphasized that the C-FRP ropes can easily be applied in structures with complex configuration without any geometrical restraints. Full article
(This article belongs to the Special Issue Advances in Building Materials and Concrete, 2nd Edition)
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23 pages, 5219 KiB  
Article
Multivariate Data Analysis of Maximum Stress Concentration Factors in FRP-Retrofitted Two-Planar KT-Joints under Axial Loads for Offshore Renewables
by Esmaeil Zavvar, Fernanda Sousa, Francisco Taveira-Pinto and Paulo Rosa Santos
J. Mar. Sci. Eng. 2024, 12(8), 1451; https://doi.org/10.3390/jmse12081451 - 22 Aug 2024
Cited by 13 | Viewed by 1735
Abstract
With growing concerns about the danger of global climate change and worldwide demand for energy, the interest in the investigation and construction of renewable energy technologies has increased. Fixed platforms are a type of support structure for wind turbines composed of different types [...] Read more.
With growing concerns about the danger of global climate change and worldwide demand for energy, the interest in the investigation and construction of renewable energy technologies has increased. Fixed platforms are a type of support structure for wind turbines composed of different types of tubular joints. These structures are under different kinds of cyclic loadings in ocean environmental conditions, which must be designed and reinforced against fatigue. In the present paper, the relationships between the parameters in DKT-joints reinforced with FRP under axial loads are investigated using several models, under 16 axial loading cases, with different nondimensional parameters and different FRP materials, and orientations were generated in ANSYS (total 5184) and analyzed. The four loading conditions that cause the maximum stress concentration factors were selected. After analyzing the 1296 reinforced models, relevant data were extracted, and possible samples were created. The extracted data were used in a multivariate data analysis of maximum stress concentration factors. The Pearson correlation coefficient is utilized to study the relationship between parameters and subsequently to make predictions. To reduce the number of variables and to group the data points into clusters based on certain similarities, hierarchical and non-hierarchical classifications are used, respectively. Full article
(This article belongs to the Special Issue Development and Utilization of Offshore Renewable Energy)
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12 pages, 2821 KiB  
Article
Machine-Learning-Based Predictive Models for Punching Shear Strength of FRP-Reinforced Concrete Slabs: A Comparative Study
by Weidong Xu and Xianying Shi
Buildings 2024, 14(8), 2492; https://doi.org/10.3390/buildings14082492 - 12 Aug 2024
Cited by 6 | Viewed by 1736
Abstract
This study is focused on the punching strength of fiber-reinforced polymer (FRP) concrete slabs. The mechanical properties of reinforced concrete slabs are often constrained by their punching shear strength at the column connection regions. Researchers have explored the use of fiber-reinforced polymer reinforcement [...] Read more.
This study is focused on the punching strength of fiber-reinforced polymer (FRP) concrete slabs. The mechanical properties of reinforced concrete slabs are often constrained by their punching shear strength at the column connection regions. Researchers have explored the use of fiber-reinforced polymer reinforcement as an alternative to traditional steel reinforcement to address this limitation. However, current codes poorly calculate the punching shear strength of FRP-reinforced concrete slabs. The aim of this study was to create a robust model that can accurately predict its punching shear strength, thus improving the analysis and design of composite structures with FRP-reinforced concrete slabs. In this study, 189 sets of experimental data were collected, and six machine learning models, including linear regression, support vector machine, BP neural network, decision tree, random forest, and eXtreme Gradient Boosting, were constructed and evaluated based on goodness of fit, standard deviation, and root-mean-square error in order to select the most suitable model for this study. The optimal model obtained was compared with the models proposed by codes and the researchers. Finally, a model explainability study was conducted using SHapley Additive exPlanations (SHAP). The results showed that random forests performed best among all machine learning models and outperformed existing models suggested by codes and researchers. The effective depth of the FRP-reinforced concrete slabs was the most important and proportional to the punching shear strength. This study not only provides guidance on the design of FRP-reinforced concrete slabs but also informs future engineering practice. Full article
(This article belongs to the Section Building Energy, Physics, Environment, and Systems)
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25 pages, 10396 KiB  
Article
Seismic Response of RC Beam-Column Joints Strengthened with FRP ROPES, Using 3D Finite Element: Verification with Real Scale Tests
by Emmanouil Golias, Paul Touratzidis and Chris G. Karayannis
CivilEng 2024, 5(2), 395-419; https://doi.org/10.3390/civileng5020020 - 30 Apr 2024
Cited by 4 | Viewed by 2038
Abstract
A 3D-finite element analysis within the numerical program ABAQUS is adopted in order to simulate the seismic behavior of reinforced concrete beam-column joints and beam-column joints strengthened with CFRP ropes. The suitability of the adopted approach is investigated herein. For this purpose, experimental [...] Read more.
A 3D-finite element analysis within the numerical program ABAQUS is adopted in order to simulate the seismic behavior of reinforced concrete beam-column joints and beam-column joints strengthened with CFRP ropes. The suitability of the adopted approach is investigated herein. For this purpose, experimental and numerical cyclic tests were performed. The experiments include four reinforced concrete (RC) joints with the same ratio of shear closed-stirrup reinforcement and two different volumetric ratios of longitudinal steel reinforcing bars. Two joints were tested as-built, and the other two were strengthened with CFRP ropes. The ropes were applied as Near Surface Mounted (NSM) reinforcement, forming an X-shape around the joint body and further as flexural reinforcement at the top and bottom of the beam. The purpose of the externally mounted CFRP ropes is to allow the development of higher values of concrete principal stresses inside the joint core, compared with the specimens without ropes, and also to reduce the developing shear deformation in the joint. From the results, it is concluded that X-shaped ropes reduced the shear deformation in the joint body remarkably, especially in high drifts. Further, as a result of the comparisons between the yielded outcome from the attempted nonlinear analysis and the observed response from the tests, it is deduced that the adopted method sufficiently describes the whole behavior of the RC beam-column connections. In particular, comparisons between experimental and numerical results of principal stresses developing in the joint body of all examined specimens, along with similar comparisons of force displacement envelopes and shear deformations of the joint body, confirmed the adequacy of the applied finite element approach for the investigation of the use of CFRP-ropes as an efficient and easy-to-apply strengthening technique. The findings also reveal that the connections that have been strengthened with the FRP ropes demonstrated improved performance, and the crack system preserved its load capacity during the reversal loading tests. Full article
(This article belongs to the Special Issue Feature Papers in CivilEng)
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25 pages, 6163 KiB  
Article
Investigation of Key Parameters Influencing Shear Behavior in Glass-Fiber-Reinforced Polymer (GFRP)-Reinforced Concrete (RC) Interior Slab–Column Connections
by Loai Alkhattabi, Nehal M. Ayash, Mohamed Hassan and Ahmed Gouda
Buildings 2024, 14(5), 1251; https://doi.org/10.3390/buildings14051251 - 28 Apr 2024
Cited by 2 | Viewed by 1586
Abstract
This article explores the punching shear behavior of GFRP-RC interior slab–column connections. The parameters tested included the column–aspect ratio (1.0, 2.0, 3.0, 4.0, and 5.0), perimeter-to-depth ratio for square column stubs with side lengths of 0.3, 0.4, 0.5, 0.6, and 0.7 m, and [...] Read more.
This article explores the punching shear behavior of GFRP-RC interior slab–column connections. The parameters tested included the column–aspect ratio (1.0, 2.0, 3.0, 4.0, and 5.0), perimeter-to-depth ratio for square column stubs with side lengths of 0.3, 0.4, 0.5, 0.6, and 0.7 m, and span-to-depth ratios of 4, 6, 8, 10, and 12. A review of the literature revealed that no previous study has investigated the effect of these parameters or their interactions on this type of connection. Numerically, twenty-five slabs were created using finite element (FE) software (V3), each with square dimensions of 2.5 m and a constant thickness of 0.2 m. The central column extended 0.3 m from the top and bottom of the slab. All four sides of the slabs were supported, and the specimens underwent pure static shear load testing. The test results demonstrated that all slabs failed due to punching shear. Increasing any parameter value reduced the punching shear stresses. Additionally, the results indicated that Canadian (CSA-S806-12) and Japanese (JSCE-97) standards for FRP-RC materials generally provided the closest predictions of punching shear capacity compared to the American guideline, ACI 440.1R-22. However, all standards exhibited shortcomings and require enhancement and modifications, particularly to consider the impact of the span-to-depth ratio. Therefore, three equations were developed to predict the shear strength of the connections, yielding better results than those prescribed by the North American and Japanese standards. Full article
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18 pages, 5616 KiB  
Article
Punching Shear of FRP-RC Slab–Column Connections: A Comprehensive Database
by Yazan Almomani, Roaa Alawadi, Ahmad Tarawneh, Abdullah Alghossoon and Ahmad Aldiabat
J. Compos. Sci. 2024, 8(4), 145; https://doi.org/10.3390/jcs8040145 - 12 Apr 2024
Cited by 1 | Viewed by 3350
Abstract
Several design standards have been developed in the last two decades to estimate the punching capacity of two-way reinforced concrete (RC) slabs reinforced with fiber-reinforced polymer (FRP) reinforcement. FRP-RC design standards include the recently published ACI 440.11-22, CSA/S806-12, and JSCE-2007. These models are [...] Read more.
Several design standards have been developed in the last two decades to estimate the punching capacity of two-way reinforced concrete (RC) slabs reinforced with fiber-reinforced polymer (FRP) reinforcement. FRP-RC design standards include the recently published ACI 440.11-22, CSA/S806-12, and JSCE-2007. These models are either based on empirical data or semi-empirical methods and calibrated using different databases. Additionally, these standards do not have provisions for connections with shear reinforcement. Therefore, a reliable worldwide database for developing and assessing the applicability of such provisions with test results is vital. This study presents a worldwide and up-to-date database for punching shear of FRP-RC slabs. The database includes 197 tested connections, comprising interior and edge connections, with and without shear reinforcement, and a wide range of materials and cross-sectional properties. The database was used to evaluate the accuracy of the mentioned standards in predicting the punching shear capacity. For connections without shear reinforcement, it was determined that the three design standards yielded similar performance with different conservatism levels. ACI 440.11-22 yielded the most conservative results, with average Vexp/Vpred ratios of 2.04 compared to 1.28 and 1.3 for other models. For connection with shear reinforcement, specimens with Evf> 100 GPa resulted in Vexp/Vpred ratios less than 1.0 for ACI and CSA standards. Full article
(This article belongs to the Special Issue Polymer Composites and Fibers, Volume II)
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20 pages, 5718 KiB  
Article
Experimental and Numerical Investigation on Flexural Strengthening of Precast Concrete Corbel Connections with Fiber-Reinforced Plastic Sheet
by Nima Rahgozar and Navid Rahgozar
Buildings 2024, 14(2), 387; https://doi.org/10.3390/buildings14020387 - 1 Feb 2024
Cited by 2 | Viewed by 1793
Abstract
This paper presents the results of experimental and numerical investigations aimed at enhancing the flexural capacity of Precast Concrete Corbel Beam–Column Connections (PC-CBCCs) using Fiber-Reinforced Plastic (FRP) sheets. The experimental study primarily focused on assessing the flexural capacity of pinned PC-CBCCs reinforced with [...] Read more.
This paper presents the results of experimental and numerical investigations aimed at enhancing the flexural capacity of Precast Concrete Corbel Beam–Column Connections (PC-CBCCs) using Fiber-Reinforced Plastic (FRP) sheets. The experimental study primarily focused on assessing the flexural capacity of pinned PC-CBCCs reinforced with FRP layers, comparing them to a moment-resisting connection. A series of half-scale specimens, including three PC-CBCCs with varying FRP configurations, were tested alongside one in situ concrete fixed connection. The first specimen (PC-1) utilized L-shaped and full-wrap FRPs, whereas PC-2 and PC-3 employed both U-shaped and full-wrap layers. The objective is to quantify the ultimate flexural capacity of PC-CBCCs reinforced by FRP sheets. In PC-3, the external anchorage is introduced to assess its influence on delaying the FRP layer debonding under lateral loading. The effects of the FRP layer thickness, locations, and potential debonding are examined under unidirectional static tests while applying a constant axial compressive load to the columns and subjecting the beams to lateral loads until fracture. The test results illustrate that strengthening the corbel connection with L-shaped FRP or spiral U-shaped FRP sheets without mechanical anchorage cannot result in a significant bending capacity due to debonding. However, with the incorporation of mechanical anchors, the connection manages to enhance the moment capacity to 81% of a fixed connection’s flexural capacity. Additionally, a finite element model of the PC-CBCCs and a fixed joint is developed to simulate nonlinear static analyses of the connections using ANSYS 19.2 software. The simulation model is precise in predicting the initial stiffness and ultimate capacity of the beam–column joints, as verified by the experimental results. A comprehensive comparison is conducted to determine their responses by employing various FRP configurations and properties. Moreover, design parameters such as bond length and thickness of the FRP sheets, along with appropriate mechanical anchorage, are identified as effective in preventing debonding, and delamination. However, wrapping the beam far away from the joint interface has a minimal impact on the failure mode, stress reduction, and load-bearing capacity. Full article
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