Journal of Composites for Construction

Glass fiber–reinforced polymer (GFRP) reinforcements can be used as shear friction connectors at the interface of concrete composite elements to maintain structural integrity. However, the shear friction mechanism at the interface greatly depends on the interface condition and the stiffness of the reinforcement crossing the interface plane. A total of 18 GFRP-reinforced concrete (RC) push-off specimens were constructed and tested until failure under monotonic load. The test parameters included the shear plane condition (roughened or not roughened, cold joints and monolithic), type (steel and GFRP), and ratio (0.24%–0.47%) of reinforcement crossing the shear plane. Roughening the interface had a little effect on the overall behavior and shear capacity of the specimen. Conversely, the monolithic specimens carried approximately 60% higher load than their cold-joint counterparts; nevertheless, the failure was more brittle. The capacity prediction by the Canadian Highway Bridge Design Code showed conservative results. By contrast, the predictions of the American Concrete Institute’s model for steel-RC elements overestimated the test results for cold-joint and monolithic specimens with reinforcement ratios of 0.43% or higher.

Understanding the stress distribution within concrete structures under complex loading conditions is crucial for investigating their failure mechanisms and ultimate strength design. Nevertheless, internal-stress distribution measurements in concrete are very challenging. This study addresses this issue by employing an innovative pressure mapping sensor to directly measure the axial stress distribution in concrete subjected to both uniform and nonuniform confining stresses. These different confinement conditions were achieved by applying fiber-reinforced polymer jackets to concrete specimens with various cross-sectional shapes. The obtained stress patterns reveal that the stress distribution within concrete depends not only on the instantaneous confining stress field but also on the stress path applied to concrete. In situations of inadequate confinement, stress concentration within an effectively confined area results in premature and severe damage, which subsequently leads to that concrete within the ineffective confinement region playing a major role in stress resistance, exhibiting a higher axial stress distribution. This finding contradicts the widely accepted notion that high stress always occurs in the effective confinement area. A series of local stress–strain curves corresponding to effective and ineffective confinement areas were also obtained, providing insights into the variation in load resistance contribution during the loading process. Furthermore, a comparison between test data and finite-element analysis results exposes disparities in the predicted stress distribution, underscoring limitations in the employed capacity of the concrete plastic-damage model to simulate concrete heterogeneity and its damage process under weak confinement. The stress distribution data presented in this study hold critical significance for comprehending concrete material failure mechanisms, advancing constitutive theories, and establishing corresponding mechanical models.

Enhancing the strength and ductility of metallic materials simultaneously is crucial for numerous industrial applications, yet it remains a formidable challenge due to the typical trade-off between these two properties. This study introduces an innovative approach to surmount this challenge by employing a composite bar design that leverages necking inhibition mechanisms for simultaneous improvements in both strength and ductility. The composite bars, comprising aluminum cores reinforced with spirally wound fiber-reinforced polymer (FRP) strands, were fabricated in various configurations to investigate different necking behaviors. Through uniaxial testing, the composite bars exhibited notable increases in both strength and ductility, attributed to the strategic design of the FRP winding angle and FRP content. This design effectively modulates the necking behavior, thereby enhancing the composite bars’ mechanical properties. Analysis of the strain distribution further elucidated the role of the spiral FRP strands in necking prevention. The composite bar design method outlined in this study offers a viable strategy for enhancing the mechanical performance of metallic materials, significantly reducing the risk of abrupt failure under high loads and deformations.

Hybrid fiber-reinforced polymer (FRP)–concrete–steel double-skin tubular members (DSTMs) yield much higher strength-to-weight ratios and much better corrosion resistance than traditional reinforced concrete members. The steel tube and the FRP tube in DSTMs act as propping and formwork for concrete casting, thus significantly reducing construction efforts. DSTMs have been extensively studied as columns and beams. This paper presents a study aimed at understanding the benefit of using the double-skin tubular cross section in arches. Five double-skin tubular arches (DSTAs) with a span length of 3.6 m were fabricated and tested to investigate their behavior. The test program examined the effects of section load eccentricity, eccentricity of the steel tube position in the section, thickness of the FRP tube, and diameter of the steel tube on the behavior of the DSTAs. All the DSTA specimens displayed ductile behavior. The DSTAs were found to provide a significantly higher ultimate load than corresponding steel–concrete composite arches of a similar cross section. A higher cross-sectional load eccentricity was found to reduce the ultimate load of a DSTA. A numerical model was also developed in OpenSees (2019) version 3.2.2 to predict the behavior of the DSTAs. The numerical predictions were found to agree with the experimental results reasonably well.

In the first part of the paper, a critical review of the fundamental knowledge of the debonding mechanism of externally bonded fiber-reinforced polymer (FRP) composites from a quasi-brittle substrate (such as concrete and masonry) is presented. Then, the paper focuses on five selected research topics. Some of these topics have reached a quite mature state. However, the authors build upon their research carried out in the last 20 years and the work published in the literature to present new perspectives or clarify aspects that have not yet reached a shared consensus. Among these five topics, the following two topics are discussed more extensively and advances in their knowledge are proposed: (1) the specific features of the interfacial law (interfacial shear stress versus slip relationship) and its shape required to obtain a finite length of the stress-transfer zone and (2) the relationship between the bond capacity in direct shear tests and the force in the FRP strip corresponding to the full debonding of FRP-strengthened beams.

Abstract

The interface shear transfer mechanism in concrete structures has been studied for several decades and its investigation has served as the basis for the provisions of current design specifications. However, most of the studies on interface shear transfer have used steel bars as interface shear reinforcement, with minimal experimental and analytical research conducted on glass fiber–reinforced polymer (GFRP) reinforcement. In this study, tests were conducted to quantify the contribution of GFRP rebars to interface shear transfer by using the push-off test. A total of 27 specimens were built and tested using a single concrete compressive strength of 36.5 MPa (5,300 psi); 9 of them included no reinforcement crossing the shear plane, 6 had steel stirrups, and 12 had GFRP stirrups with two quantities of reinforcement. Additionally, during the construction process, six of the specimens were built in two stages to simulate a cold joint condition at the interface. The experimental results showed that GFRP reinforcement contributes substantially to the interface shear strength with ultimate resistance values higher than the results from specimens without reinforcement. Furthermore, once the ultimate strength is reached, the GFRP reinforcement allows the specimen to deform and prevent sudden failure. As for the theoretical capacities estimated by current codes, the experimental tests for GFRP showed an overestimation in the calculation of these capacities. Therefore, the research findings will be helpful in the development and improvement of design guide specifications for concrete structures reinforced with GFRP stirrups where interface shear effects are significant.

Practical Applications

Numerous concrete structures depend on the effective transfer of shear forces at joints where concrete sections may slide past one another. This is particularly crucial in scenarios such as bridge construction, where a precast, prestressed concrete girder must seamlessly integrate with the reinforced concrete deck. Ensuring this connection can adequately handle shear forces is vital for the structure’s overall stability and integrity. While the shear-friction mechanism, a key aspect of the design of reinforced concrete structures, has been extensively explored with steel reinforcement, research on GFRP reinforcement has been limited. This study focuses on experimental investigations to understand how GFRP influences shear-friction behavior. Although numerous factors can affect shear-friction performance, this research primarily aims to clarify the fundamental behavior of shear-friction when using GFRP reinforcement. The findings suggest that it is important to consider the effect of reinforcement stiffness in tension, rather than its strength.

For unidirectional laminates, four properties are required for mechanical characterization regarding the laminae elastic response: the longitudinal elastic modulus, the transverse elastic modulus, the in-plane shear modulus, and the in-plane Poisson's ratio. Two approaches are usually followed to obtain these properties: an experimental program, which is costly and time-consuming, or micromechanical modeling, which is associated with many uncertainties. The trace theory has been widely explored for carbon fiber-reinforced polymers as an alternative option, where only one independent property is necessary and the others are obtained using a normalized relation with the trace of the stiffness matrix. Considering the wide application of glass fiber-reinforced polymers (GFRPs) in civil structures, an extension of the trace theory was developed by combining micromechanics and machine learning. First, a data set was generated using the asymptotic homogenization for the usual properties ranges of glass fibers and polymeric matrices. Next, the decision trees algorithm was implemented to evaluate the normalized properties variation according to the trace. Based on the results of the training procedure, linear equations were obtained for the normalized properties. The proposed equations were validated by comparing the estimations of the normalized properties with a set of 17 experimental data compiled from the literature, indicating that the average errors range between 3% and 13%. Once the proposed equations were validated, the novel theory was applied to analyze the buckling load of thin-walled structures, where square and channel profiles with different stacking sequences were evaluated. Only the longitudinal elastic modulus was used as input, while the other properties were computed using the trace relations. The properties computed analytically were applied in a finite-element model to calculate the buckling loads, resulting in average errors of this hybrid approach smaller than 10% for both profiles.

Abstract

A steel strand wire mesh (SSWM)–reinforced engineered cementitious composite (ECC), referred to as SSWM-ECC, is a promising composite material for structural strengthening owing to the combination of the high strength of SSWM and the high ductility of ECC. This paper presents an application of SSWM-ECC for shear strengthening of reinforced concrete (RC) beams subjected to cyclic loading. First, cyclic loading tests were conducted on two control beams and five strengthened beams, considering various shear span-to-effective depth ratios, reinforcement ratios of the SSWM, and strengthening schemes. The test results showed that brittle failure and degradation of the shear properties of the strengthened beams were effectively mitigated. Compared to the control beams, the ultimate load, cracking load, service load, ductility, and energy absorption of the strengthened beams increased by 18%–40%, 145%–208%, 35%–126%, 20%–65%, and 58%–96%, respectively. The improvement in shear performance increased with increasing reinforcement ratio of the SSWM and shear span-to-effective depth ratio. In addition, the fully wrapped strengthening method effectively confined the concrete, resulting in a more significant increase in the shear performance of the beams compared to the U-wrapped and both-sided methods. Furthermore, a modified truss arch model was developed to predict the shear strength of the strengthened beams. The results predicted by the proposed model exhibited greater accuracy than those generated by various existing models, including those commonly utilized in the field.

Practical Applications

The experimental study presented in this paper demonstrates a significant improvement in the shear performance of RC beams subjected to cyclic loading using a novel composite called SSWM-ECC. This method is expected to be useful for structural strengthening. The fully wrapped, U-wrapped, and both-sided SSWM-ECC strengthening methods introduced in this paper are applicable to a wide range of engineering projects. In particular, an economical and convenient method for strengthening RC beams using externally bonded prefabricated SSWM-ECC plates is presented. The SSWM-ECC can effectively mitigate the shear brittleness of RC beams subjected to cyclic loading and significantly increase their shear strength, stiffness, cracking resistance, energy absorption, and ductility. Furthermore, the strengthening efficiency increased with increasing shear span-to-effective depth ratio and reinforcement ratio of the SSWM. Finally, a calculation method for predicting the shear strength of strengthened beams is proposed, which provides a basis for the design and application of shear strengthening of RC beams with SSWM-ECC under cyclic loading.

Even though many experimental studies have evidenced that fiber-reinforced polymer (FRP)-confined concrete columns under compression might exhibit a postpeak strain-softening response, followed by a hardening behavior (a stress reduction–recovery response), most existing models are only applicable to confined columns developing full hardening behavior. Additionally, their applicability is limited to a certain column cross-sectional shape (circular or noncircular). Therefore, the present study is dedicated to the establishment of a new design-oriented stress–strain model, unified for FRP-confined circular/noncircular concrete columns. For this purpose, first, a new nondimensional confinement stiffness-based index is developed, below which the column response is transformed from a full-hardening behavior (Type A) to a postpeak strain softening–hardening one (Type B). A parabolic-linear stress–strain formulation is proposed for Type A columns by developing a new expression for the calculation of the linear hardening branch’s slope. For the case of Type B, a new methodology is introduced for the simulation of the stress reduction–recovery response beyond the transition zone, whose main elements are calibrated by a large test data set. The dominance degree of the noncircularity effect of the cross section on both Type A and Type B cases was assessed and reflected in the key components of the proposed stress–strain models, based on nonlinear regression analysis. With these considerations, this model could accurately simulate the impact of the noncircularity effect on the stress–strain relationship of Type A and Type B columns, whose predictive performance is validated through a comparative assessment with existing models based on large test stress–strain results.

Carbon fiber–reinforced polymer–steel composite bars (C-FSCBs) and coral sea-sand aggregate seawater concrete (CSSC) are attractive choices as construction materials for island and atoll engineering construction. Understanding the bond behavior between the C-FSCB and CSSC is crucial for evaluating the mechanical properties of C-FSCB-reinforced CSSC structures. In this study, the bond–slip behavior between the C-FSCB and CSSC was experimentally assessed via pullout tests. The influence of various factors on the bond behavior was discussed, and the bond mechanism between the C-FSCB and CSSC was analyzed. The results indicate that, unlike steel bars, the low rigidity of fiber-reinforced polymer caused surface fiber stripping (i.e., shear damage) of the C-FSCB after interface slip, consequently reducing the squeezing fragmentation of concrete between the ribs. As the diameter and bond length of the C-FSCB increased, the bond strength decreased. Compared to specimens with C-FSCBs, the bond strength of specimens with steel bars of the same diameter increased by 17.9%. The degree of coarse aggregate fracture at the CSSC interface in the splitting failure was much higher than that of normal concrete. Based on existing research data, a formula for calculating the bond strength of C-FSCBs in CSSC has been established to determine the anchorage length of C-FSCBs, and the calculated values accurately predicted the test values.

Abstract

The use of large-format three-dimensional (3D) printed thermoplastic composites as formworks for precast concrete structures has emerged as a cost-effective solution addressing challenges related to skilled labor shortages and enabling design optimization. This research work investigates the technical feasibility of recycling large-format 3D printed polymer composite formworks. Thermomechanical recycling of 3D printed formworks was implemented and the recycled polymer composite feedstock was used to 3D print new formworks. Two commonly used short-fiber reinforced polymer composite materials were evaluated: one petroleum-based material, carbon fiber–filled acrylonitrile butadiene styrene (CF-ABS), and one biobased material, wood flour–filled amorphous polylactic acid (WF-aPLA). Mechanical properties of 3D printed specimens were characterized to evaluate their suitability as 3D printed formworks. Physical and thermal characterization methods were used to understand the change in thermal and mechanical properties of the thermoplastic polymers due to the recycling process. The study also employed similar methods to assess the potential contamination of polymer composites with cementitious materials. Results revealed that high-pressure water washing was effective in removing cementitious material from the formwork surface, and the recycled material did not show significant contamination. Thermomechanical recycling was shown to reduce the fiber length of reinforcing fibers and the molecular weight of the polymer material. The reduction in fiber length and the molecular weight of the material results in the reduction of material viscosity. The observed reductions in viscosity have the potential to limit the number of recycling iterations. However, thermal stability was maintained throughout all processing levels. In addition, the mechanical performance of the WF-aPLA material system was observed to increase after the recycling process. However, the mechanical performance of the CF-ABS material system was observed to decrease after recycling. Recycled 3D printed formworks were found to work effectively, albeit some reduction in mechanical properties of recycled formworks was observed.

Practical Applications

Large-format three-dimensional (3D) printed polymer composite formworks have been used to cast precast concrete structures. Currently, the formworks are disposed of in a landfill, once they have been used to cast the necessary number of precast concrete parts. If the 3D printed formworks could be recycled to make new formworks, the material cost of 3D printed thermoplastic composites could be significantly reduced while also making 3D printed formworks environmentally friendly. This research assesses the viability of thermomechanical recycling and reusing 3D printed thermoplastic composite formworks. The changes in material properties of thermomechanically recycled composites were studied. The effectiveness of cleaning the formwork using high-pressure water wash was investigated and the efficacy of using recycled 3D printed thermoplastic formwork was evaluated. The steps involved in manufacturing large format 3D printed formwork and recycling are described, and the challenges in each of these steps are discussed.

Bridges situated in northern climate regions, which face severe environmental conditions and daily fatigue loading, are prone to accelerated deterioration and corrosion of their components. The application of carbon fiber–reinforced polymer (CFRP) sheets bonding to the surface of bridge elements has emerged as an attractive solution for enhancing bridge strength. Past studies and field implementations have effectively showcased the viability of this approach in strengthening bridges. An exceptional opportunity arises with the deconstruction of a bridge in Canada, providing a unique chance to assess and study the condition of reinforced concrete elements strengthened with CFRP. These elements have endured real service conditions, including fatigue loads and exposure to aggressive environmental factors. This paper presents the experimental results of a research program that aimed to investigate the residual fatigue life and capacity of 60-year-old reinforced concrete bridge girders, which were strengthened using CFRP sheets. The study focuses on assessing the performance of these girders under different test conditions, providing valuable insights into their remaining fatigue life and load-carrying capabilities. The two 60-year-old girders have been strengthened with CFRP for the last 10 years of the service life of the bridge. The two full-scale girders were tested under 2 million fatigue load cycles and then tested monotonically until failure at the structural lab of the University of Sherbrooke. The test results revealed that the CFRP-strengthening technique can extend the service life of the bridge element and enhance its shear capacity. The CFRP–concrete interface and CFRP sheets showed excellent bonding behavior, as no damage-debonding failure or tensile rupture occurred until the formation of the diagonal shear crack.

This paper defines a conversion factor included in the European technical specification for the design of fibre–polymer composite structures that considers the effects of moisture on the mechanical properties of fiber-reinforced polymer (FRP) composites exposed to natural weathering. The first part of the paper presents a field investigation about the durability of four pultruded glass fiber–reinforced polymer (GFRP) structures in service for 11–22 years in a Mediterranean climate. Their performance was evaluated by dynamic mechanical analysis and mechanical tests on small-scale coupons. The changes of thermophysical and mechanical properties showed low-to-moderate degradation. The second part of the paper presents the design-oriented methodology to define the moisture conversion factor. The results from the experimental study and those gathered from a literature data survey on the retention of mechanical properties of FRP materials after long-term exposure to natural weathering were analyzed. Based on these data and statistical considerations, a value of 0.85 was adopted for the natural weathering moisture conversion factor.

The application of fiber-reinforced polymer (FRP) composites as piling materials in harsh environments has gained popularity due to their high corrosion resistance. FRP composites can be fabricated using different types of epoxy resin matrices and fibers. This study aims to investigate the interface behavior between sand and FRP materials with varying levels of hardness, with a particular emphasis on the abrasive surface wear of FRP. Monotonic interface shear tests (under normal stresses of 50, 100, 200, and 400 kPa) and interface shear tests repeated 20 times (under normal stresses of 200 and 400 kPa) are performed. The local surface roughness of the FRP plates is measured for tested samples under both monotonic and repeated loadings using laser scanning to evaluate the accumulated abrasion effect. The results of monotonic tests indicate that under a given shear displacement and normal stress, the samples with softer FRP plates exhibit higher interface friction angles and more pronounced dilative behavior. Following repeated tests, the interface friction angles of softer FRP specimens decrease, while the surface roughness of the FRP plates gradually increases. However, for the softest FRP plate, its surface is severely damaged after repeated tests under high normal stress levels, leading to unstable changes in the test results.

Novel fiber-reinforced polymer (FRP) bar-reinforced ultrahigh-performance engineered cementitious composites (UHPECCs) have been proposed recently. This innovative composite structure aims to address two critical challenges: (1) the reduced stiffness in FRP-reinforced normal concrete stemming from the lower elastic modulus of FRP; and (2) corrosion concerns faced by steel-reinforced concrete structures. Despite various investigations into the long-term performance of glass fiber–reinforced polymer (GFRP) bars in concrete environments, typically conducted through immersion in simulated concrete pore solutions, the durability of GFRP bars within UHPECCs remains unexplored. The inherently reduced water permeability of UHPECCs raises expectations for the enhanced protection they will provide to internal GFRP bars. Therefore, this study explores the durability performance of GFRP bars embedded in UHPECCs. Three types of GFRP bars made of various matrices (polyester, vinyl ester, and epoxy) were employed. The embedded GFRP bars were immersed in an alkaline solution at room temperature and 40°C for a duration of up to 360 days. Their tensile properties were assessed after specified periods. The results indicated a more pronounced deterioration in GFRP bars made of polyester than bars made of epoxy and vinyl ester. UHPECC covers provided good protection for internal GFRP bars compared with ordinary concrete due to the reduced permeability of UHPECCs. A microstructural analysis revealed that bar deterioration was predominantly due to matrix hydrolysis. This phenomenon resulted in the efficiency of fiber stress transfer. Notably, fibers in UHPECC-embedded GFRP bars exhibited no evident degradation, whereas those in the bars without UHPECC covers displayed slight degradation.

Predicting the shear resistance of reinforced concrete (RC) beams strengthened with externally bonded reinforcement using carbon fiber–reinforced polymer (CFRP) materials poses a significant challenge due to the complex nonlinear relationship with beam features and the inherent randomness in shear failure events, driven by their brittle nature. This paper proposes a model employing a multiobjective optimization technique that both, enhances the accuracy and ensures unbiased predictions. To highlight the achieved improvement, a comparison is made between the performance of the proposed model and a series of well-established models in the literature. The proposed model presents superior predictive performance and a smaller coefficient of variation in the model error distribution than the models in the literature. In addition, it exhibits unbiased predictions, highlighting the advantages of incorporating multiobjective optimization. Furthermore, a modified demerit point classification is introduced and applied to all models, highlighting the superiority of the proposed model in producing more reliable and cost-effective predictions.

Hybrid double-skin tubular columns (DSTCs) are a promising form of composite columns in which the concrete is sandwiched between inner steel and outer fiber-reinforced polymer (FRP) tubes. A modified form of DSTC incorporating stiffened steel tubes demonstrates more potential benefits than the standard unstiffened design. The inclusion of stiffeners in the steel tube enhances composite interaction among column components, effectively delaying local buckling deformations and potentially improving the behavior of confined concrete. The present study performs both experimental and analytical investigations to measure the impact of stiffeners on the confined concrete behavior of square-circle (SC) configured specimens, considering various column slenderness ratios. Thirty DSTC specimens were experimentally tested with variations in steel stiffener properties, including number, configuration (maintaining a similar combined area), thickness, and width; and unconfined concrete strength. The test results showed a substantial improvement in axial load capacity in the stiffened SC-shaped specimens, reaching up to approximately 37% in this study. Subsequently, the test data were utilized to propose a stress–strain confined concrete model specific to SC-shaped specimens with varying slenderness ratios. This proposed model was employed for calibration study using detailed finite-element (FE) analysis, demonstrating excellent agreement with the test data. A parametric investigation was then conducted through FE analysis to optimize the rib-stiffener properties. Finally, the findings from both the experiments and the FE analysis were utilized to develop a simplified equation that predicts the axial load capacity of stiffened SC-DSTCs.

Abstract

Steel-reinforced concrete (RC) columns typically exhibit significant residual displacements and low postyield stiffness when subjected to seismic loads, which may complicate subsequent repairs. This paper investigated the effects of different reinforcement methods on the seismic performance of concrete columns by using glass fiber–reinforced polymer (GFRP) and basalt fiber–reinforced polymer (BFRP) bars. Five samples were subjected to low-cycle horizontal loading tests to compare the corresponding seismic performance indices. The results showed that fully FRP-reinforced concrete columns had a lower energy dissipation capacity and ductility coefficient than RC columns but had other clear advantages in terms of ultimate displacement and a postyield stiffness increase by 100%. Compared to RC columns, the concrete columns with half FRP bars exhibited comparable energy dissipation, greater ultimate displacements and ductility coefficients, and a 60% increase in postyield stiffness. Incorporating FRP bars significantly reduced the residual deformation of FRP-reinforced concrete columns compared to RC columns under the same loading cycle, enabling structural repairs and continued use after an earthquake.

Practical Applications

During the 2008 Wenchuan earthquake, many traditional reinforced concrete structures were severely damaged, causing significant economic losses and threatening lives and property. Related investigations verified that the deformation of reinforced concrete columns was the most serious under the same displacement level, and adding fiber-reinforced polymer materials greatly reduced the deformation of the concrete columns, which can improve the reparability of the structure after an earthquake. Additionally, the peak load-carrying capacity of fiber-reinforced polymer materials is similar to that of reinforced concrete columns, giving the former a certain application value. In the coastal areas of traditional reinforced concrete structures, because of corrosion, which leads to a significant reduction in the service life of the environment, it is proposed that the introduction of fiber-reinforced polymer materials with excellent corrosion resistance will largely improve the service life of the corrosive environment of the components while ensuring similar seismic performance.

This paper examines experimental data from 22 large-scale concrete-filled FRP tubes (CFFTs), each 900 mm in length and 300 mm in diameter, subjected to either concentric or eccentric compression. The study encompasses CFFTs composed of normal-strength concrete (NSC) and high-strength concrete (HSC), employing glass fiber–reinforced polymer (GFRP) tubes with fiber angles of 60° and 80°. A primary focus of this study is investigating the cracking behavior of GFRP tubes in CFFTs during loading, a durability/serviceability-related issue that has received limited attention in existing literature. Based on the test data, the study identifies two distinct types of cracking: tension-induced cracking under eccentric compression and hoop crushing under either concentric or eccentric compression. The paper delves into the underlying mechanisms behind these cracking phenomena and thoroughly explores the influence of variables such as fiber-reinforced polymer (FRP) tube thickness, fiber angle, and the type of concrete core on the observed cracking behavior. Meanwhile, the paper provides an in-depth analysis of the structural behavior of CFFTs, with a focus on aspects such as GFRP tube thickness, fiber angle, and the differences between NSC and HSC cores. These experimental results not only enhance the understanding of the behavior of large-scale CFFTs under concentric or eccentric compressions but also offer crucial insights into the differences in the compressive behavior of FRP-confined NSC columns and FRP-confined HSC columns. Additionally, the comparative analyses of local cracking behavior with the global behavior of CFFTs contribute vital information toward the development of a design method of CFFT columns in practice, with different considerations of the issues in the ultimate limit state and serviceability limit state (e.g., the corrosion protection capabilities of the GFRP tube in CFFTs).

Aiming to address anchoring challenges associated with carbon fiber–reinforced polymer (CFRP) tendons used as cables, this study introduces a three-segment structure CFRP-bonded anchorage and conducts tests. Building upon the verified accuracy of a finite-element (FE) model, the mechanisms underlying CFRP cable failure are analyzed. Finally, four key parameters—CFRP tendon clear spacing, friction coefficient, elastic modulus of the bonding medium, and pretension force—were selected to optimize the CFRP cable stress distribution and enhance the anchoring effectiveness. The research findings indicate that the three-segment structure anchor design achieves effective anchoring for multitendon CFRP cables, with a mean efficiency exceeding 98%. Observations during testing indicated uneven stress among the anchor system’s inner and outer layer CFRP tendons, and FE analysis suggests that the uneven stress primarily manifests as nonuniform axial stress and contact shear stress. The former may lead to failure in CFRP tendons due to the combined tension–bending stress, while the latter may result in interface failure, causing CFRP tendon slippage. Comparative analysis of stress and displacement distribution between inner and outer layer CFRP tendons in the anchor zone elucidates the mechanism of uneven stress, attributing it to the displacement lag effect between layers of CFRP tendons. Further parameter optimization indicates that applying pretension force to CFRP tendons effectively reduces uneven stress, improving the degree of combined tension–bending stress in the CFRP tendons at the loading end.