Most of the existing studies conducted on FRP-confined concrete considered circular and square concrete columns, while limited studies were on columns with rectangular sections. The studies have confirmed that the circular cross-sections exhibited higher confinement effectiveness, whereas in the case of non-circular cross-sections the efficiency of FRP confinement decreases with an increase of the sectional aspect ratio and there is no significant increase, particularly for columns with the aspect ratio of 2.0. As recently suggested by the researchers, to significantly increase the effectiveness of FRP-confinement for these columns is by modifying a rectangular section to an elliptical or oval section. According to the literature, most of the existing confinement models for FRP-confined concrete under axial compression have been proposed for columns with circular and rectangular cross-sections. However, modeling the axial strength and strain of concrete confined with FRP in elliptical cross-sections under compression is most limited. Therefore, this paper provides new expressions based on limited experimental data available in the literature. For a sufficient amount of FRP-confinement, the threshold value was proposed to be 0.02. Finally, the accuracy of the proposed model was verified by comparing its predictions with the same test database, together with those from the existing models.

All over the world, externally bonded fiber-reinforced polymer systems used to strengthen concrete elements improve building sustainability. However, reports issued by the American Concrete Institute Committee 440 called for heavy scrutinizing before actual field implementation. The very limited number of proposed equations lacks reliability and accuracy. Thus, further investigation in this area is needed. In addition, machine learning techniques are being implemented successfully in developing strength models for complex problems. This study aims to provide a reliable machine learning model based on an experimental database. The proposed model was developed and validated against the experimental database and the very limited models in the literature. The model showed improved agreement with the experimental results compared to the previous models.

Renovation, restoration, remodeling, refurbishment, and retrofitting of build-ings often imply modifying the behavior of the structural system. Modification sometimes includes applying forces (i.e., concentrated loads) to beams that before were subjected to distributed loads only. For a reinforced concrete structure, the new condition causes a beam to bear a concentrated load with the crack pattern that was produced by the distributed loads that acted in the past. If the concentrated load is applied at or near the beam’s midspan, the new shear demand reaches the maximum around the midspan. But around the midspan, the cracks are vertical or quasi-vertical, and no inclined bar is present. So, the actual shear capacity around the midspan not only is low, but also can be substantially lower than the new demand. In order to bring the beam capacity up to the demand, fiber-reinforced-polymer composites can be used. This paper presents a design method to increase the concentrated load-carrying capacity of reinforced concrete beams whose load distribution has to be changed from distributed to concentrated, and an analytical model to pre-dict the concentrated load-carrying capacity of a beam in the strengthened state.

This paper presents the results of experimental and numerical investigations aimed at enhancing the flexural capacity of Precast Concrete Corbel Beam-Column Connections (PC-CBCC) 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 objective was to quantify the ultimate flexural capacity of PC-CBCCs reinforced by FRP sheets. The effects of FRP layer thickness, locations, and potential debonding were examined under unidirectional static tests while applying a constant axial compressive load to the columns and subjecting the beams to lateral loads until fracture. Additionally, a precise finite element model of the PC-CBCCs and a fixed joint was developed and verified to simulate nonlinear static analyses of the connections in ANSYS software. A comprehensive comparison was conducted to determine their responses by employing various FRP configurations and properties. The tests and numerical results demonstrate that wrapping PC-CBCCs with anchored FRPs can transform pin connections into moment-resistant joints. Moreover, critical design parameters such as bond length, thickness, and placement of FRP sheets, along with appropriate mechanical anchorage, are identified to prevent debonding and delamination.

The masonry building Heritage is appreciated for its aesthetic and historical value all around the world. The widespread presence of curved elements, such as arch, vault and dome express the relevant constructive abilities in the different historical epochs. These curved elements are characterized by architectural beauty, structural strength (especially against the gravity loads), thermal comfort and fire resistance. On the other hand, curved structures required scaffolding in order to be erected. The design, the construction and the dismantling of the scaffolds is typically time-consuming and expensive. In addition, the on-site working risk is related to time-interferences (e.g. in manpower working, at the same time, over and under scaffold). This technology dates back to the Era of the Roman Empire and it is currently still used, despite its limitations and disadvantages. In the present paper, an innovative technique (recently patented), aiming for the construction of a curved structural member without scaffolds, is proposed and illustrated. It consists in a Hinged Lifting Arch (HLA), using FRP (Fiber Reinforced Polymer) bonded strips. In details, a series of blocks are cut following an arch geometry and then aligned on the ground-floor in order to bond a composite on their top surface. Moreover, the impregnation of the polymeric adhesive is not allowed at the extremities of each block. The fiber sheet is applied continuously along the entire extrados. In this sense, hinges are introduced, in fact, the FRP-connected blocks are able to easily rotate, in the opposite direction, around the contact ends (i.e. hinge). Finally, the middle block is lifted-up and the arch takes the desiderated shape. In the first experimental demonstration, the natural calcareous stone was used, even if the proposed technique is totally material-independent. Moreover, an analytical model is proposed and discussed for designing the proper aspect ratio of the blocks in order to ensure the full mutual contact when the HLA is totally lifted up. The advantages of the proposed technique are related to the absence of scaffolds and improved seismic strength against horizontal loads thanks to the presence of the FRP, which limits the occurrence of hinges at the extrados.

Steel reinforcement in concrete has the tendency to corrode and this process can lead to structural damage. FRP reinforcement represents a viable alternative for structures exposed to aggressive environments and has many possible applications where superior corrosion resistance properties are required. The use of FRP rebars as internal reinforcements for concrete, however, is limited to specific structural elements and does not yet extend to the whole structure. The reasons for this relate to the limited availability of curved or shaped reinforcing elements on the market and their reduced structural performance. Various studies, in fact, have shown that the mechanical performance of bent portions of composite bars is reduced significantly under a multiaxial combination of stresses and that the tensile strength can be as low as 25% of the maximum tensile strength that can be developed in the straight part. In a significant number of cases, the current design recommendations for concrete structures reinforced with FRP, however, were found to overestimate the bend capacity of FRP rebar. This paper presents the state-of-the art review of the research works on the strength degradation in curved FRP composites and highlighted the performance of exiting predictive models for the bend capacity of FRP reinforcement. Recent practical predictive model based on the Tsai-Hill failure criteria by considering the material at marcromechanical level is also discussed and highlighted. The review also identifies the challenges and highlights the future directions of research to explore the use of shaped FRP composites in civil engineering applications and the trends for future research in this area.

In order to address the issues of weight, cost and sustainability issues associated with the application of glass fibre in structural composites, plant fibres are proposed as an alternative to reduce and replace the usage of glass fibres. Despite this, there is still a gap in comprehensive research on plant fibre composites, especially with regard to their durability in real structural applications. This research investigates the fatigue and impact properties of pultruded hybrid polyester composites reinforced with glass fibre and kenaf, tailored for structural applications. Utilising kenaf fibres in mat form, unidirectional glass fibre direct roving yarns and unsaturated polyester resin as key components, pultruded kenaf/glass hybrid profiles were meticulously fabricated. Comparative cost and weight analyses were conducted between pultruded hybrid and non-hybrid profiles. The study showed that the pultruded kenaf/glass alternative laminates exhibit commendable fatigue and impact resistance, making them suitable for use in moderately loaded structural applications. Moreover, the use of kenaf as a hybrid alternative shows significant cost and weight reductions. This research provides a basis for the development of sustainable and efficient structural materials and highlights the significant role of material design in shaping the future of engineering applications.

This paper deals with analyzing the structural responses of glass-fiber-reinforced polymer (GFRP) tubes filled with recycled and concrete material for developing composite piles, as an alternative to traditional steel reinforced piles in bridge foundations. The Full-scale GFRP composite piles included three inner and outer layers, using a fiber-oriented material that was inclined longitudinally, almost 40 degrees from the horizontal axis of the pile. The segment between these two layers was inclined 80 degrees from the longitudinal axis of the tube. The behavior of the filled GFRP tubes was semi-linear, and resulted in increasing the total ductility and strength of the piles. Adjusting the material’s properties, such as the EAxial, EHoop, and Poisson ratios optimized the results. The lateral strength of the GFRP composite pile and pre-stressed piles are comparable in both axial and lateral loading conditions.

An experimental study was carried out to evaluate the ductility of reinforced concrete beams longitudinally reinforced with hybrid FRP-Steel bars. The specimens were fourteen reinforced concrete beams with and without hybrid reinforcement. The test variables were bars position, the ratio of longitudinal reinforcement, and the type of FRP bars. The beams were loaded up to failure using a four-point bending test. The performance of the tested beams was observed using the load-deflection curve obtained from the test. Numerical analysis using the fiber element model was used to examine the growth of neutral axis depth due to the effect of test variables. The neutral axis curves were then used to further estimate the neutral axis angle and neutral axis displacement index. The test results show that the position of the reinforcement greatly influences the flexural behavior of the beam with hybrid reinforcement. It was observed from the test that the flexural capacity of beams with hybrid reinforcement is 4% to 50% higher than that of the beams with conventional steel bars depending on bars position and the ratio of longitudinal reinforcement. The ductility decreases as the hybrid reinforcement ratio (Af/As) increases. This study also showed that a numerical model developed can predict the flexural behavior of beams with hybrid reinforcement with reasonable accuracy.

An increasing use of non-metallic reinforcement is problematic as it has to be detected at the stage of accepting construction works, or later when expert opinions are prepared for the building. In contrast to metallic reinforcement, location of this type of reinforcement is difficult using non-destructive techniques. Small diameters of rebars and their location in a tested element were troublesome. This article describes an attempt to locate non-metallic reinforcement in a concrete element and the masonry. Tests were performed using an ultrasonic tomograph and GPR with a broad range of frequencies.

As the general acceptance of fiber-reinforced polymer (FRP) in the concrete construction industry continues to rise, it is increasingly imperative that the crack width of FRP reinforced concrete members of pavement and girder be predicted with good accuracy due to strengthening of RC pavement, slabs or beams structures using FRP is known to control crack width. However, no specific provisions are provided by most international design codes for predicting crack width in FRP reinforced concrete flexure members. In this paper, five formulas for predicting the crack width for FRP reinforced structures are derived from three common computational theories which including statistical method, comprehensive theory, and bond-slip theory. The formula of statistical method is simplest, but the parameters depend on much sample data. The comprehensive and slippage theory based on semi-empirical statistical crack spacing are obtained through the calculation of non-uniformity coefficient of strain. The comprehensive and slippage theory based on semi-empirical axial force balance are obtained through the calculation of tensile reinforcement factor. The comparative analysis of performance of five formulas is carried out. The results indicate that the formula from comprehensive theory based on semi-empirical statistical crack spacing is recommended for predicting the crack width of FRP reinforced concrete flexural structure.

The objective of this paper is to investigate the debonding behavior of the interface between continuously and discontinuously fiber reinforced thermoplastics using the climbing drum peel test. The study emphasizes the importance of considering different climatic boundary conditions due to the properties of thermoplastics. Specimens with varying moisture contents are prepared and tested. It is observed that an increase in moisture content initially results in a higher fracture surface energy being required to separate the two materials, but a further increase results in a decrease of the required energy. The study presents an explanatory model of increasing plasticization of the polymer due to increased polymer chain mobility, which results in more deformation energy being required to propagate the crack. The experiment is also modeled numerically for the first time with cohesive surfaces, which successfully reproduces the force-displacement curve in the experiment.

As is well known, the main contribution of the FRP strips to the strength of load-bearing walls is an improvement in the in-plane strength. This paper deals with the possibility of applying the FRP strips in way to modify the strengthening mechanism of the FRP reinforcing system, from an in-plane to an out-of-plane strengthening mechanism. In order to achieve this goal, a second reinforcement system – derived from the CAM system (Active Confinement of Masonry) – provides connections between the FRP strips placed on the opposite sides of the wall. This new strengthening technique – called the straps/strips technique – establishes a stiffness constraint that forces the opposing FRP strips to behave like two flanges of an FRP I-beam embedded in the wall. Consequently, the use of FRP strips also improves the flexural strength of the wall. The present paper briefly summarizes the results obtained in previous works with the straps/strips technique and proposes an improvement of this strengthening technique, based on some weak-points emerged in the early experimentations. The paper also shows the results of a further experimental test, performed with the improved straps/strips technique. Finally, the similarity between FRP strips with transversal connection and concrete wythes of a sandwich panel with flexible connectors leads to interpret the behavior of the ideal I-beam in terms of composite action established between the FRP strips. This paves the way for analytical modeling of the straps/strips technique.

This study presents a comprehensive comparative analysis of retrofitting techniques aimed at enhancing the seismic resilience of seismically vulnerable historical buildings. Recognizing the dual objectives of structural safety and architectural preservation, this research evaluates and compares several advanced retrofitting methods, including base isolation, strengthening of masonry, steel bracing systems, Fiber-Reinforced Polymer (FRP) wrapping, and damping devices. Each technique is critically assessed based on its effectiveness in mitigating seismic risks, its compatibility with historical architectural features, and its applicability to various building types. Base isolation is highlighted for its ability to decouple buildings from ground motion, thereby significantly reducing seismic forces and protecting architectural integrity. Strengthening of masonry through the use of fiber-reinforced polymers and steel elements enhances the ductility and strength of masonry walls, making them more resilient to seismic forces. Steel bracing systems are shown to provide essential lateral support, particularly in timber-framed structures, improving overall stability and reducing deformation during earthquakes. FRP wrapping is identified as a versatile technique that strengthens structural elements without compromising aesthetic value, making it suitable for reinforcing concrete and masonry components. Damping devices, including viscous dampers and tuned mass dampers, are discussed for their ability to dissipate seismic energy and control structural vibrations, offering a minimally invasive solution that preserves historical aesthetics. The study also addresses several challenges and research gaps associated with these retrofitting techniques, such as ensuring architectural compatibility, assessing long-term material performance, optimizing cost-effectiveness, and navigating complex regulatory frameworks. By advancing knowledge in these areas, the research aims to foster interdisciplinary collaboration and innovation in the development of retrofitting solutions. Ultimately, this study contributes to the ongoing efforts to safeguard historical buildings against seismic hazards. By leveraging cutting-edge technologies and best practices in structural engineering and architectural conservation, stakeholders can develop sustainable, cost-effective, and culturally sensitive retrofitting strategies that protect valuable cultural heritage for future generations.

Keywords: Wall-like RC columns; Strengthening; FRP; NSM rebars; Steel plates; Testing; FE modeling; Preloading.

The durability of bridge decks is a critical factor in ensuring the safety and longevity of transportation infrastructure. This article explores advanced materials and innovative techniques designed to mitigate cracking in bridge decks, a common issue that can compromise structural integrity and increase maintenance costs. It provides a comprehensive review of cutting-edge solutions such as Fiber-Reinforced Polymers (FRP), High-Performance Concrete (HPC), Ultra-High Performance Concrete (UHPC), and self-healing concrete technologies. Each material is analyzed for its ability to enhance strength, reduce permeability, and improve resistance to environmental stressors. Additionally, the article examines the role of surface treatments, sealants, and routine maintenance practices in prolonging the life of bridge decks. By synthesizing current research and practical applications, this article offers valuable insights and recommendations for engineers, contractors, and policymakers seeking to advance bridge deck durability through innovative materials and methodologies.