Search Results (417)

Reinforced concrete (RC) deep beams constructed with low-strength concrete are susceptible to sudden splitting failures in the strut region due to shear–compression stresses. To mitigate this vulnerability, various strengthening techniques, including steel plates, fiber-reinforced polymer sheets, and cementitious composites, have been explored to confine the strut area. This study investigates the structural performance of RC deep beams with low-strength concrete, strengthened externally using an Engineered Cementitious Composite (ECC) layer. To ensure effective confinement and uniform shear distribution, shear reinforcement was provided at equal intervals with configurations of zero, one, and two vertical shear reinforcements. Four-point bending tests revealed that the ECC layer significantly enhanced the shear capacity, increasing load-carrying capacity by 51.6%, 54.7%, and 46.7% for beams with zero, one, and two shear reinforcements, respectively. Failure analysis through non-linear finite element modeling corroborated experimental observations, confirming shear–compression failure characterized by damage in the concrete struts. The strut-and-tie method, modified to incorporate the tensile strength of ECC and shear reinforcement actual stress values taken from the FE analysis, was used to predict the shear capacity. The predicted values were within 10% of the experimental results, underscoring the reliability of the analytical approach. Overall, this study demonstrates the effectiveness of ECC in improving shear performance and mitigating strut failure in RC deep beams made with low-strength concrete. Full article

Using lightweight concrete (LWC) reduces the dead weight of the concrete structure by 25–30% compared to ordinary concrete. However, harmful and corrosive substances penetrate the lightweight concrete matrix due to its high permeability, resulting in higher maintenance costs and a reduced structure service life. Therefore, in harsh environments where conventional steel bars are susceptible to corrosion, fibre-reinforced polymer (FRP) bars should be used for reinforcement. However, there is a paucity of experimental studies regarding LWC structural elements reinforced with FRP bars. Shear strength is a critical limit state that typically determines the proper design of such elements, ensuring the required safety margin and an appropriate level of reliability. The research work was conducted to compare the experimentally determined shear strengths (V_exp) of 50 structural elements (beams, slabs) made of LWC/FRP with code predictions (V_code) made according to eight codes used for design. Based on this comparison, the so-called conformity coefficient (V_exp/V_code) was calculated and used to assess which provision documents are the best, considering the entire population of test results. The work demonstrated that the recent Eurocode best predicts the shear strength of LWC/FRP elements. Full article

The construction industry is exploring alternatives to traditional steel reinforcement in concrete due to steel’s corrosion vulnerability. Glass Fiber Reinforced Polymer (GFRP) and Basalt Fiber Reinforced Polymer (BFRP), known for their high tensile strength and corrosion resistance, are viable options. This study evaluates the flexural performance of concrete beams reinforced with GFRP, BFRP, and hybrid systems combining these materials with steel, following ACI 440.1R-15 guidelines. Twelve beams were assessed under three-point bending to compare their flexural strength, ductility, and failure modes against steel reinforcement. The results indicate that GFRP and BFRP beams achieve 8% and 12% higher ultimate load capacities but 38% and 58% lower deflections at failure than steel, respectively. Hybrid reinforcements enhance both load capacity and deflection performance (7% to 17% higher load with 11% to 58% lower deflection). However, GFRP and BFRP beams show reduced energy absorption, suggesting that hybrid systems could better support critical applications like seismic and impact-prone structures by improving ductility and load handling. In addition, BFRP beams predominantly failed due to debonding and concrete crushing, while GFRP beams failed due to bar rupture, reflecting key differences in their flexural failure mechanisms. Full article

Despite the strength and ductility of steel reinforcing bars, their susceptibility to corrosion can limit the long-term durability of reinforced concrete structures. Fiber-reinforced polymer (FRP) reinforcing bars made with a thermosetting matrix offer corrosion resistance but cannot be field-bent, which limits flexibility during construction. FRP reinforcing bars made with fiber-reinforced thermoplastic polymers (FRTP) address this limitation; however, their high processing viscosity presents manufacturing challenges. In this study, the Continuous Forming Machine, a novel pultrusion device that uses pre-consolidated fiber-reinforced thermoplastic tapes as feedstock, is described and used to fabricate 12.7 mm nominal diameter thermoplastic composite rebars. Simple bend tests on FRTP rebar that rely on basic equipment are performed to verify its ability to be field-formed. The manual bending technique demonstrated here is practical and straightforward, although it does result in some fiber misalignment. Subsequently, surface deformations are introduced to the rebar to promote mechanical bonding with concrete, and tensile tests of the bars are conducted to determine their mechanical properties. Finally, flexural tests of simply-supported, 6 m long beams reinforced with FRTP rebar are performed to assess their strength and stiffness as well as the practicality of using FRTP rebar. The beam tests demonstrated the prototype FRTP rebar’s potential for reinforcing concrete beams, and the beam load–deformation response and capacity agree well with predictions developed using conventional structural analysis principles. Overall, the results of the research reported indicate that thermoplastic rebars manufactured via the Continuous Forming Machine are a promising alternative to both steel and conventional thermoset composite rebar. However, both the beam and tension test results indicate that improvements in material properties, especially elastic modulus, are necessary to meet the requirements of current FRP rebar specifications. Full article

Glass Fiber-Reinforced Polymer (GFRP) bars are becoming increasingly common in structural engineering applications due to their superior material properties, mainly their resistance to corrosion due to their metallic nature in comparison to steel reinforcement and their improved durability in alkaline environments compared to CFRP and BFRP reinforcement. However, GFRP bars also suffer from a few limitations. One of the main issues that affects the performance of GFRP reinforcing bars is their bond with concrete, which may differ from the bond between traditional steel bars and concrete. However, despite the wide attention of researchers, there has not been a critical review of the recent research progress on bond behavior between GFRP bars and concrete. The objective of this paper is to provide an overview of the current state of research on bond in GFRP-reinforced concrete in an attempt to systematize the existing scientific knowledge. The study summarizes experimental investigations that directly measure bond strength and investigates the different factors that influence it. Additionally, an overview of the analytical and empirical models used to simulate bond behavior is then presented. The findings indicate the dependence of the bond on several factors that include bar diameter, bar surface, concrete strength, and embedment length. Additionally, it was concluded that both traditional and more recent bond models do not explicitly account for the effect of different factors, which highlights the need for improved bond models that do not require calibration with experimental tests. Full article

Fiber-reinforced polymer (FRP) bars have great potential to replace steel bars in the design of reinforced concrete (RC) beams since they have numerous advantages such as high tensile strength and good corrosion resistance. Therefore, many studies including experiments and numerical simulations have focused on the behavior of FRP RC beams. In this paper, a comprehensive overview of previous studies is conducted to provide a thorough understanding about the behavior, the design, and the limitations of FRP RC beams. Particularly, experimental studies on FRP RC beams are collected and reviewed. In addition, the numerical analysis of FRP beams including the finite element (FE) analysis, the discrete element (DE) analysis, and artificial intelligence/machine learning (AI/ML) is summarized. Moreover, the international standards for the design of FRP RC beams are presented and evaluated. Through the review of previous studies, 93 tested specimens are collected. They can be a great source of reference for other studies. In addition, it has been found that the studies on the continuous beams and deep beams reinforced with FRP bars are still limited. In addition, more studies using DE analysis and AI/ML to analyze the response of FRP RC beams under loading conditions should be conducted. Full article

This study investigates the thermal performance of 23 different mortar types, each containing different mixes, properties, and additives. A comprehensive literature review was conducted to collect experimental data on the thermal properties of these mortars, which were then used in a numerical analysis through thermal finite element modeling. The results showed that all mortar types contributed to reducing the internal temperature of structural steel and reinforced concrete elements, with performance primarily influenced by key factors such as the mortar’s thermal conductivity, specific heat capacity, thermal diffusivity, and coating thickness. In particular, the mortar with glass fiber reinforced polymer (GFRP) as a slag substitute and the mortar with expanded perlite replacing sand showed the highest thermal protection and achieved a temperature reduction on the order of 100%. In contrast, mortars containing 30% vermiculite or 15% light expanded polyvinyl chloride (PVC) as a sand substitute showed the lowest thermal performance. Full article

The growing application of carbon fiber-reinforced polymers (CFRPs) in construction opens new possibilities for replacing traditional materials such as steel, particularly in strengthening and retrofitting concrete structures. CFRP materials offer notable advantages, including high tensile strength, low self-weight, corrosion resistance, and the ability to be tailored to complex geometries. This paper provides a comprehensive review of current technologies used to strengthen concrete columns, with a particular focus on the application of fiber-reinforced polymer (FRP) tubes in composite column systems. The manufacturing processes of FRP composites are discussed, emphasizing the influence of resin types and fabrication methods on the mechanical properties and durability of composite elements. This review also analyzes how factors such as fiber type, orientation, thickness, and application method affect the load-bearing capacity of both newly constructed and retrofitted damaged concrete elements. Furthermore, the paper identifies research gaps concerning the use of perforated CFRP tubes as internal reinforcement components. Considering the increasing interest in innovative column strengthening methods, this paper highlights future research directions, particularly the application of perforated CFRP tubes combined with external composite strengthening and self-compacting concrete (SCC). Full article

The use of both structural steel and reinforced concrete is common in civil and military infrastructure projects. Anchorage plays a crucial role in these systems, serving as the key element that connects structural components and secures attachments within complex composite structures. This research focuses on evaluating the performance of steel–concrete column connections under the combined effects of lateral loading and fire exposure. Additionally, the study investigates the use of carbon fiber-reinforced polymers (CFRP) for strengthening and repairing these connections. The research methodology combines experimental testing and finite-element modeling to achieve its objectives. First, experimental investigation was carried out to test two groups of steel-reinforced concrete column specimens, each group made of three specimens. The first group specimens were designed based on special moment frame (SMF) detailing, and the other group specimens were designed based on intermediate moment frame (IMF) detailing. These two types of design were selected based on seismic demands, with SMFs offering high ductility and resilience for severe earthquakes and IMFs providing a cost-effective solution for moderate seismic zones, both benefiting from ongoing innovations in connection detailing and design approaches. Then, finite-element analysis was conducted to model the test specimens. High-fidelity finite-element modeling was conducted using ANSYS program, which included three-dimensional coupled thermal-stress analyses for the six tested specimens and incorporated nonlinear temperature-dependent materials characteristics of each component and the interfaces. Both the experimental and numerical results of this study show that fire has a more noticeable effect on displacement compared to the peak capacities of both types of specimens. Fire exposure results in a larger reduction in the initial residual lateral stiffness of the SMF specimens when compared to IMF specimens. While the effect of CFRP wraps on initial residual lateral stiffness was consistent for all specimens, it caused more improvement for the IMF specimen in terms of post-fire ductility when compared to SMF specimens. This exploratory study confirms the need for further research on the effect of fire on the concrete–steel anchorage zones. Full article

Noncorrosive concrete reinforcement, such as polymer fibers, is needed to overcome the current issues caused by corroded steel reinforcements. Fibers made of polypropylene show a low bonding behavior in concrete. Fillers can help to overcome this issue but often lead to reduced mechanical properties. Core-shell fibers, which split the mechanical properties and the bonding behavior between the core and the shell component, could be a solution. This study investigates mono-material and core-shell fibers produced with calcium carbonate and bentonite fillers and compares their behavior in tensile tests, density measurements, contact angle measurements, topography measurements, single fiber pull-out tests, reflected light microscopy, and thermogravimetric analysis. The fillers caused an increased drawability, resulting in higher mechanical properties. Further, in the core-shell fibers, the calcium carbonate increased the surface roughness, which led to a better anchoring of the fiber in concrete, which was also visible in the deformation during pull-out observed in reflected light microscopy pictures. The thermogravimetric analysis showed a delay in onset of degradation for fibers containing bentonite. Full article

Traditional fiber-reinforced polymer (FRP) retrofit methods can restore the strength of reinforced concrete columns well, but stiffness is also partly restored. To increase the initial stiffness of retrofitted columns, this study investigated the seismic behavior of retrofitted resilient reinforced concrete (RRC) columns that were retrofitted by different methods, including high-strength mortar retrofit, carbon fiber-reinforced polymer (CFRP) retrofit, and CFRP and steel plate retrofit. In addition, the effect of the axial load was also considered. Quasi-static tests were conducted twice on five specimens, i.e., before and after repairing. The first test was used to create earthquake damage, and the second test was used to compare the seismic behavior of the retrofitted columns. The experimental results indicated that the CFRP retrofit method, whether with a steel plate or not, can restore the lateral resistance capacity well; furthermore, the drift-hardening behavior and self-centering performance were well maintained. The residual drift ratio of the CFRP-retrofitted column was less than 0.5%, even at a drift ratio of 3.5%, and less than 1% at the 6% drift ratio. However, the initial stiffness was only partly restored using the CFRP sheet. The introduction of steel plates was beneficial in restoring the initial stiffness, and the stiffness recovery rate remained above 90% when CFRP sheets and steel plates were used simultaneously. The strain distribution of the CFRP sheet showed that the steel plate did work at the initial loading stage, but the effect was limited. By using the steel plate, the CFRP hoop strain on the south side was reduced by 68% at the 6% drift ratio in the push direction and 38% in the pull direction. The axial strain of CFRP cannot be ignored due to the larger value than the hoop strain, which means that the biaxial stress condition should be considered when using an FRP sheet to retrofit RC columns. Full article

Reinforced concrete structures often require retrofitting due to damage caused by natural disasters such as earthquakes, floods, or hurricanes; deterioration from aging; or exposure to harsh environmental conditions. Retrofitting strategies may involve adding new structural elements like shear walls, dampers, or base isolators, as well as strengthening the existing components using methods such as reinforced concrete, steel, or fiber-reinforced polymer jacketing. Selecting the most appropriate retrofit method can be complex and is influenced by various factors, including initial cost, long-term maintenance, environmental impact, and overall sustainability. This study proposes utilizing an artificial neural network (ANN) to predict sustainable and cost-effective seismic retrofit solutions. By training the ANN with a comprehensive dataset that includes jacket thickness, material specifications, reinforcement details, and key sustainability indicators (economic and environmental factors), the model was able to recommend optimized retrofit designs. These designs include ideal values for jacket thickness, concrete strength, and the configuration of reinforcement bars, aiming to minimize both costs and environmental footprint. A major focus of this research was identifying the optimal number of neurons in the hidden layers of the ANN. While the number of input and output neurons is defined by the dataset, determining the right configuration for hidden layers is critical for performance. The study found that networks with one or two hidden layers provided more reliable and efficient results compared to more complex architectures, achieving a total regression value of 0.911. These findings demonstrate that a well-tuned ANN can serve as a powerful tool for designing sustainable seismic retrofit strategies, helping engineers make smarter decisions more quickly and efficiently. Full article

The increasing demand for sustainable construction materials has driven the exploration of alternatives to traditional cement-based concrete. In this context, this study investigates a cement-less material, specifically an alkali-activated or geopolymer concrete (GPC), which presents potential environmental benefits. The material has been characterized with respect to both its fresh and hardened properties, providing groundwork for future structural applications. A key focus of the research is the bond behavior between GPC and reinforcing bars, including both steel and non-metallic fiber-reinforced polymer (FRP) bars. The use of non-metallic bars is particularly relevant as they offer the potential to enhance the durability of structures by mitigating issues such as corrosion. Current research lacks comprehensive studies on factors affecting stress transfer at the GPC-reinforcing bar interface, such as bar diameter, bond length, and surface finish. This study aims to expand knowledge on the bond between GPC and steel/FRP rebars through experimental and analytical approaches. The tests, which included different bar types and bond lengths, showed that GPC exhibited similar bond behavior with steel and ribbed glass FRP bars in terms of bond strength and stress-slip curves. The results indicate that GPC exhibits comparable bond strength and stress-slip behavior when reinforced with either steel or ribbed glass FRP bars. Full article

With growing emphasis on sustainable construction, fiber-reinforced polymer (FRP) bars are increasingly being used as alternatives to steel rebars due to their high strength-to-weight ratio, corrosion resistance, and environmental benefits. This study has investigated the bond behavior between FRP bars and concrete of different strength grades under dynamic loading conditions. To analyze the microscopic properties of FRP bar surfaces, the study employs a variety of techniques, including scanning electron microscopy (SEM), atomic force microscopy (AFM), and non-contact surface profilometry. In addition, X-ray photoelectron spectroscopy (XPS), water contact angle (WCA) measurements, and energy dispersive spectrometry (EDS) are used to further investigate surface characteristics. The results reveal a direct correlation between the resin surface roughness of FRP bars and their wettability characteristics, which in turn influence the cement hydration process. Pull-out tests under different loading rates and concrete strength grades have been conducted to evaluate the bond–slip behavior and failure modes. The results indicate that bond strength increases with increasing concrete strength. Dynamic pull-out tests further reveal that higher loading rates generate heterogeneous stress fields, which limit the deformation of FRP bars and consequently diminish the contribution of mechanical interlock to interfacial bonding. Full article

Based on the research on concrete-filled circular steel tubular columns, the influence of carbon-fiber-reinforced polymers (CFRPs) on the ultimate bearing capacity of concrete-filled steel tubes (CFSTs) was further explored in this paper. Ten different concrete-filled circular CFRP–steel middle long columns were made for an axial compression test, and the influence of the CFRP layers, the concrete strength grades, the steel tube wall thickness, and the slenderness ratio on the ultimate bearing capacity was discussed. Combined with theoretical analysis, the calculation method of ultimate bearing capacity of it was found. The load midspan deflection diagram was obtained by numerical simulation with finite element analysis software ANSYS2021R1, and the test results were compared. The results demonstrate that CFRP layers significantly enhance the ultimate bearing capacity of circular steel tube–CFRP confined concrete columns, with one to three layers increasing the capacity by 42.5%, 69.4%, and 88.4%, respectively, under identical conditions. In comparison, the concrete strength, the steel tube thickness, and the slenderness ratio showed lesser effects (<20% improvement), providing critical support for engineering applications of CFRP-confined circular steel tubular columns. Moreover, the error of ANSYS calculation results is small, which is in line with the test. This is of great significance to verify the correctness of the test of concrete-filled circular CFRP–steel middle long columns. Full article