Fiber-reinforced Polymer Rupture Research Articles

Behavior of concrete voussoir flexible arch bridges reinforced with FRP composites

Flexible arch bridges, which can be pre-fabricated, transported and assembled on-site, have become increasing popular. This study presents an experimental investigation into the behavior of concrete voussoir flexible arch bridges reinforced with fiber-reinforced polymer (FRP) sheets by loading four arch specimens to failure at their left third-spans. The variables included the concrete voussoir strengths, bond quality between FRP and concrete voussoirs, and the FRP reinforcement locations. The results showed that two specimens with good bonding between FRP sheets and concrete voussoirs failed from sudden FRP rupture, while the other two specimens experienced FRP debonding and ultimately exhibited a four-hinge collapse mechanism. For the specimens with good FRP bonding, the typical load-deflection curve obtained at the loading point was an approximately monotonic increasing line, while load reductions and recoveries, as well as slope deteriorations were noted for the specimens experienced FRP debonding. It is also compared that bond quality could be more important than concrete voussoir strength, as the specimens with good bonding had higher ultimate load capacities. Applying one additional FRP sheet at intrados of arch could significantly enhance the initial ascending slope by 100%, but it cannot enhance the peak load as the FRP sheet at extrados of arch was more efficiently utilized in preventing more hinge formations at extrados joints.

A review on retrofitting concrete members with near‐surface mounted‐fiber reinforced polymer composites

AbstractIn an era flooded with a multitude of studies investigating the performance of concrete structures retrofitted using fiber‐reinforced polymer (FRP) materials, this review addresses the critical need for a comprehensive overview of the retrofitting of concrete members using near‐surface mounted (NSM)‐FRP composites, aiming to save time and effort while providing engineers and research community with valuable resources relevant to the field. This review focuses on the key factors influencing both the flexural and shear retrofitting processes of reinforced concrete (RC) beams, such as the percentage, type, size and geometry of NSM‐FRP reinforcement, as well as groove design, groove‐filling materials and beam depth. Moreover, the paper explores the failure modes associated with each retrofitting type, for example, debonding failures, shear/flexural failure and rupture of steel or NSM‐FRP reinforcement, to name a few. The review also delves into the bond behavior of NSM‐FRP‐bonded joints, examining factors, such as the bonded length, surface texture of NSM‐FRP reinforcement and type of bonding agent, which would affect the bond behavior and strength of the joints. The failure mechanisms associated with the bonded joints, such as interfacial bond failure, FRP rupture and splitting of the adhesive cover, are also highlighted. Finally, this compilation aims to guide engineers and researchers by offering a critical and comprehensive database for optimal designs, further development and suggesting future research directions.

A novel double bridging-slipping (DBS) concept to overcome deformation incompatibility of textile reinforced-engineering cementitious composite (TR-ECC)

Due to the deformation incompatibility between the engineering cementitious composite (ECC) matrix and embedded fiber reinforced polymer (FRP), conventional textile reinforced (TR)-ECC usually fails in premature FRP rupture when subjected to a tensile load. To address this issue, a novel double bridging-slipping (DBS)-based concept is proposed in this study. Apart from bridging-slipping capacity of incorporated short fibers in the ECC matrix, the presence of FRP strip can contribute to the other bridging-slipping mechanism for enhancing the tensile performance of the whole specimen. The embedment zone of FRP strips can bridge the crack tips of ECC matrix through the FRP-ECC interfacial bond stress, and the slippage of FRP strips in the uncracked zone can compensate for the excessive deformation of ECC matrix in the multi-cracking zone. Experimental results show that compared to the conventional TR-ECC, the proposed DBS-based TR-ECC with the same FRP volumetric ratio of 0.113 % can significantly improve the ultimate tensile strain and toughness by 148.3 % and 38.0 %, respectively. As DBS-based TR-ECC facilitates the combination of superior strength of FRP textiles and excellent toughness of ECC materials, it has a promising application in infrastructure projects.

A REVIEW ON FLEXURAL STRENGTHENING OF REINFORCED CONCRETE BEAMS WITH PRESTRESSED NEAR SURFACE MOUNTED CFRP LAMINATE

Reinforced structures are subjected to tremendous loading, which causes early deterioration, and replacing RC structures on before the end of intended life is prohibitively expensive. The application of fiber- reinforced polymer (FRP) composites to strengthen damaged structural components is obtaining favour in the construction industry because to their better strength, durability, and compatibility with reinforced concrete structures during usage. The main purpose of this research is to examine the existing performance, problems, and further potential of CFRP-strengthened reinforced concrete structural member under various loading circumstances. FRP reinforcement outperforms in static, dynamic, and harsh environmental criteria. The most typical type of failure in reinforced beams are debonding, separation of concrete cover, and FRP rupture. Acceptance and usage of FRP in RC structure strengthening will increase further as new techniques for utilising the full strength of FRP, reducing brittleness, fire risk and damages due to accident, lowering energy consumption and during production emission of carbon, and finally reducing the initial cost are developed. This report identifies knowledge gaps as well as promising research topics for FRP- strengthened structures. Keywords: Flexural strengthening, NSM, CFRP strip, Prestressed, Failures.

Effect of compression casting method on the axial compressive behavior of FRP-confined seawater sea-sand concrete columns

The application of the novel compression casting method is beneficial to improve the compressive strength and durability of concrete. However, the compressed concrete fails rapidly after the peak load and exhibits stronger brittleness than the normal concrete, which could impair the seismic performance of the columns. As one of the passive confining measures, wrapping fiber-reinforced polymer (FRP) could be a practical technique to improve the ductility of such brittle columns. In this regard, this study experimentally investigated the axial compression behavior of both the partially and fully FRP-confined compression-cast seawater sea-sand concrete (SSC) columns. The test results indicated that the compression casting method enhanced the compressive strength but weakened the axial deformation capacity of the unconfined and FRP-confined SSC specimens. The compressive strength of unconfined concrete was improved by 38.5% due to compression casting. The measured average FRP rupture strain of the FRP-confined compression-cast SSC specimens was 6.3% smaller than that of FRP-confined normal SSC specimens due to the sudden appearance of the main oblique cracks, indicating poorer FRP utilization efficiency. Meanwhile, the average ultimate axial strain enhancement ratio of FRP-confined SSC specimens decreased from 12.04 to 7.83 after compression casting. The FRP hoop strain of the fully FRP-wrapped columns distributed more uniformly compared to the partially FRP-wrapped columns as the mean value of FRP efficiency factor increased from 0.807 to 0.928. With increasing FRP strip spacing, the post-peak segment of the stress–strain curve transferred from strain-hardening to strain-softening regardless of the confining stiffness. Finally, several existing stress–strain models were employed to examine their accuracy in anticipating the ultimate conditions of the FRP-confined compression-cast SSC columns.

Intermediate Crack Debonding of Externally Bonded FRP Reinforcement-Comparison of Methods.

Many researchers around the world have made extensive efforts to study the phenomenon of fiber-reinforced polymer (FRP) debonding. Based on these efforts, code provisions and various models have been proposed for predicting intermediate crack (IC) debonding failure. The paper presents a comparison of seven selected models: fib bulletin 14 approach, Teng et al. model, Lu model, Seracino et al. model, Said and Wu model, Elsanadedy et al. model and ACI 440. The accuracy of each model was evaluated based on the test results of 58 flexural specimens with IC debonding failures of externally bonded (EB), carbon FRP plates or sheets found in the existing literature. The experimental database was prepared to include a wide range of parameters affecting the issue under consideration. A comparison of the measured and predicted load capacity values was made to evaluate the prediction accuracy of the considered models. The analysis included the limitation of the load capacity estimated based on IC debonding models as well as concrete crushing and FRP rupture types of failure. The results indicate that the latest models proposed for direct implementation in design guidelines—the Said and Wu model and the Elsanadedy et al. model—offer the best accuracy in predicting the load capacity. In contrast, the fib bulletin 14 approach shows a wide dispersion of predictions and a large proportion of highly overestimated results.

Effect of Aggregate Size on the Axial Compressive Behavior of FRP-Confined Coral Aggregate Concrete.

Using locally available raw materials for preparing concrete, such as coral reefs, seawater, and sea sand, is conducive to compensating for the shortage of construction materials used on remote islands. Jacketing fiber-reinforced polymer (FRP), as passive confinement, is a practical approach to enhance the strength, ductility, and durability of such coral aggregate concrete (CAC). Rational and economical CAC structural design requires understanding the interactions between the CAC fracture process and FRP confinement. The coral aggregate size is the critical parameter of their interaction since it affects the crack propagation of CAC and FRP confinement efficiency. This study conducted axial compression tests on FRP-confined CAC cylinders with varying coral aggregate sizes and FRP confinement levels. The test results indicate that the coral aggregate sizes affected the unconfined CAC strength. In addition, the dilation behavior of FRP-confined CAC varied with aggregate sizes, showing that CAC with smaller coral aggregate featured a more uniform hoop strain distribution and larger FRP rupture strain. These coupling effects are epitomized by the variation in the transition stress on the stress–strain curve, which makes the existing stress–strain models not applicable for FRP-confined CAC. A modified stress–strain model is subsequently proposed. Finally, the practical and environmental implications of the present study are discussed.

Size effect on compressive behavior of FRP-confined engineered cementitious composites (ECC)

• A first-ever experimental study on the size effect of GFRP- and LRS FRP-confined ECC columns was conducted. • The influences of specimen size, FRP confinement level, and FRP type were examined. • A new size-dependent ultimate stress model of FRP-confined ECC was established. The reliable design of the high-performance column made of fiber reinforced polymer (FRP)-confined engineered cementitious composites (ECC) necessitates a clear understanding of the size effect under axial compression. This paper presents the compressive behaviors of glass FRP (GFRP) and large rupture strain (LRS) polyethylene terephthalate (PET) FRP-confined ECC columns. The specimen size, confinement level, and FRP type were the variables. Five diameters of 100, 200, 300, 400, and 500 mm were designed to cover a wide size range. Results showed that both the compressive strength and ductility of ECC were substantially improved with FRP confinement. Compared with GFRP-confined ECC, PET FRP-confined ECC exhibited higher ductility. The key stresses, namely initial peak stress, post-peak ravine stress, and ultimate stress decreased with increasing specimen size. Nevertheless, the specimen size had a marginal influence on the key strains and dilation behavior. After evaluating the existing size-dependent ultimate strength models of FRP-confined concrete, a new expression for predicting the ultimate strength of FRP-confined ECC was introduced, which was shown to fit well with the test results.

Compressive behavior degradation of FRP-confined RC columns exposed to a chlorine environment

Fiber-reinforced polymer (FRP) has been recognized as a promising method for strengthening reinforced concrete (RC) structures under a chlorine environment; however, it cannot prevent steel reinforcements from chloride-induced corrosion. Thus, the main objectives of this study were to (1) investigate the corrosion-induced performance degradation in FRP-confined RC columns under axial compression; (2) quantity the reduction of FRP rupture strain in FRP-confined RC columns subjected to a chlorine environment; and (3) propose a formula to estimate the load carrying capacity of FRP-confined RC columns considering the corrosion ratio. Twenty-eight columns with different FRP types (carbon fibre reinforced polymer (CFRP) and glass fibre reinforced polymer (GFRP)) and different layers of FRP (0, 1, 2, and 3) were conditioned under an accelerated corrosion process to obtain various corrosion ratios (0%, 5%, 10%, and 20%) and then tested under axial compression. The results showed that steel corrosion degraded the compressive response of FRP-confined RC columns, especially their deformation capacity. GFRP-confined RC columns generally had a better deformation capacity and were less vulnerable to steel corrosion than were CFRP-confined RC columns. Based on these test results, predictive equations for estimating the rupture strain of FRP were proposed as a function of corrosion ratio, which was introduced to modify an existing strength model of concrete confined with both FRP and steel stirrups. Finally, the ultimate load of FRP-confined RC columns with or without corrosion was predicted based on the modified concrete strength model.

Strain localization analysis using digital image correlation for PVA fiber-reinforced concrete-filled FRP tubes under compressive loading

This study presents the outcomes of the first experimental study on the strain localization of polyvinyl alcohol (PVA) fiber-reinforced concrete-filled fiber-reinforced polymer (FRP) tubes (CFFTs). 24 CFFT specimens were prepared and tested with various instrumentations, such as linear variable differential transformer (LVDT) and strain gauges (SGs), to record required full-field strains, i.e., axial, lateral and Von Mises strains. The strain evolutions over the surface of the specimens were recorded during axial compression loading. The FRPs were prepared with carbon, S-glass or basalt fiber to examine the influence of the fiber type and confinement stiffness on the behavior and strain localization of CFFTs. The evolution of Von Mises strains was determined and studied under axial compression. The obtained results show that although the general pattern of localization for both CFFTs without and with PVA fiber is nearly similar, the characteristics of the localization are different. The expansion of shear zone for insufficiently basalt FRP (BFRP)-confined concrete is more localized compared to the more homogenized behavior of sufficiently FRP-confined concrete. However, insufficiently BFRP-confined PVA fiber-reinforced concrete exhibits less localized behavior compared to insufficiently BFRP-confined plain concrete, which is due to the influence of the internal fibers on the concrete cracking behavior. At FRP rupture, hoop strains vary along the height and around the perimeter of the specimens, which results in the inability of SGs to consistently capture the actual hoop rupture strain.

Efficient second-order nonlinear finite-element simulation of concrete-filled FRP tubular arches

Concrete-filled fiber-reinforced polymer (FRP) tubes (CFFTs) are attractive as beams and arches in harsh environments due to their durability and ease of erection. A successful infrastructure application is the use of multiple, buried CFFT arches in short-span bridges. To effectively analyze and design CFFT arches under complex loadings, there is a need for numerical procedures that capture the structural behavior of CFFT arches including the effects of FRP confinement on the concrete core and second-order response. Here, a computationally efficient structural finite-element analysis technique for the second-order inelastic behavior of these CFFT arches is detailed. A curved, flexibility-based, layered-frame element is employed to handle geometric and material nonlinearities. A concrete constitutive model that explicitly considers the effect of dilation of the concrete core and confinement provided by the FRP tube is implemented. A bending test was performed on a CFFT arch, and experimental data compared with model predictions. Additional comparisons are made with CFFT arch and beam bending tests available in the literature. The model is shown to accurately predict the load-carrying capacity and ductility of CFFT members, and to capture arch collapse mechanisms arising from FRP rupture and concrete crushing.

Confinement model for LRS FRP-confined concrete using conventional regression and artificial neural network techniques

Concrete confined using fiber-reinforced polymer (FRP) composites experience significant enhancements in strength and strain. For the seismic retrofitting of existing reinforced concrete (RC) structures, a large rupture strain (LRS) FRP (i.e., polyethylene terephthalate and naphthalate, denoted as PET and PEN respectively), with a larger rupture strain of more than 5%, is a promising alternative to conventional FRPs with a rupture strain of less than 3%. The majority of analytical models on the stress–strain behavior of FRP-confined concrete under axial compression have focused largely on concrete confined with the traditional FRP material. Analytical research on LRS FRP-confined concrete is, however, limited. Moreover, all existed stress–strain models were determined based on theoretical analysis and test data fitting. In this paper, the artificial neural networks (ANN) method is employed to build a confinement model directly from experimental data to predict the different components of the stress–strain response. A test database consisting of 226 axial compression tests on LRS FRP-confined concrete specimens is used. The test results, in terms of full confined stress–strain response, strength, strain, FRP rupture strain, and dilation response were investigated. Predictive expressions and practical ANN models for the strength, strain, and shape of an axial stress–strain response are provided. Existing models for LRS FRP-confined concrete were also evaluated. The results of the existing and proposed models report that the proposed methods achieve significantly better results.

Axial impact behavior of Large-Rupture-Strain (LRS) fiber reinforced polymer (FRP)-confined concrete cylinders

This paper presents an experimental study on the impact performance of concrete columns confined with large-rupture-strain (LRS, tensile rupture strain ≥ 5%) fiber reinforced polymer (FRP) jackets. A total of 32 concrete specimens were prepared and tested using large-capacity drop-weight equipment. The test variables included four impact heights (2, 3, 4 and 5 m), three types of FRP, i.e., aramid FRP (AFRP), polyethylene naphthalate (PEN) FRP and polyethylene terephthalate (PET) FRP and two layers of FRP jackets (1 and 2). The time histories of impact force and FRP rupture strain as well as failure modes were obtained from the test. Compared to the AFRP-confined concrete specimen with similar jacket stiffness, the core concrete of the LRS FRP-confined specimen was less damaged due to the large-rupture-strain characteristic. The impact force increased and the impact duration decreased with increasing impact height. The impact duration of concrete specimens confined with LRS FRP was longer than that of the AFRP-confined concrete column. Results showed that the impact-resistance behaviours of LRS FRP-confined concrete column outperformed its companion column confined with AFRP. Besides, increasing the thickness of FRP jacket can enhance the impact resistance capacity. These findings may facilitate the impact resistance strengthening/retrofitting of RC structures with the application of LRS FRP composites.

Behavior and modeling of double-skin tubular columns filled by ultra-lightweight cement composites (ULCCs)

Double skin tubular columns (DSTCs) filled by ultra-lightweight cement composites (ULCCs), as primary load-bearing elements, are a practical and reasonable structural asset in lightweight civil infrastructure. This DSTC-ULCC system combines the advantages of three materials, 1) outer fiber-reinforced polymer (FRP) 1–3 ply jackets, 2) filled ULCCs, and 3) inner steel tubes to achieve lightweight, high strength and superior ductility. This article presents an experimental study on the mechanical behavior of DSTCs with FRP and ULCCs under axial compressive loading. The experiment designed a total of 26 DSTCs that were all filled with ULCCs. The key parameters were the number of FRP layers and the inner steel tube properties, (i.e., thickness and diameter of the steel tube). The test results indicate that the properties of the inner steel tube not only influences the effective FRP rupture strain ratio but also the ultimate axial strain of confined ULCCs. This calls attention to the inward buckling behavior for larger void ratios; moreover, thinner steel tubes result in more axial deformation of ULCC-filled DSTCs. In addition, ULCCs showed a much lower elastic modulus compared with normal concrete, which helped cause the change of transition stress of ULCCs in DSTCs, and FRP confinement can effectively increase the elastic length of the stress–strain curves for ULCCs. The experimental results are subsequently compared with predictions from an FRP-confined ULCC model, which led to a new ultimate strain model proposed herein for ULCC-filled DSTCs. The comparison demonstrates that the model can provide reasonably accurate predictions of the stress–strain curves of ULCCs in hollow DSTCs.

Behavior of hybrid CFST with FRP-confined UHPC core under axial compression

A fiber-reinforced polymer (FRP)-confined concrete core that provides high strength and ductility under axial compression can act as strength enhancement in a hybrid column. In the present study, ordinary concrete was replaced with ultra-high-performance concrete (UHPC) to form an FRP-confined UHPC core (FCUC). The FCUC was embedded in square concrete-filled steel tube (CFST) columns to form a high-performance hybrid column (SCF-UHPC column for short). The axial compressive behavior of the SCF-UHPC was experimentally investigated using 12 SCF-UHPC columns and two ordinary CFST columns for comparison. The advantages of the SCF-UHPC include excellent axial load-bearing capacity, good ductility, and stable residual load-bearing capacity. The results show that failure of an SCF-UHPC column was caused by FRP rupture of FCUC, which occurred after steel tube buckling that results in the degraded stiffness. It was also shown that the load-displacement behavior of the SCF-UHPC composite column was determined by the UHPC core diameter and the corresponding confinement provided by the outer steel tube and inner FRP jacket. A hardening effect could be achieved when the confinement demand of the UHPC core was satisfied, whereas a plateau effect appeared if the confinement was insufficient. Furthermore, the load-bearing capacity and ductility of the SCF-UHPC columns improved with increased thickness of the steel tube and the FRP.

Reliability analyses of shear strengthened RC beams with externally bonded fiber reinforced polymer

Different methods for the estimation of fiber reinforced polymer (FRP) contribution to shear strength in reinforced concrete (RC) beams were evaluated and compared through reliability analysis using FRP rupture and debonding failure functions. The carbon fibers properties were obtained through laboratory tests allowing to define the probability distribution function of the fiber tensile strength and elastic modulus. Uncertainties associated with the load, material properties were taken into account in order to compare two standards (ACI 440.2R and CNR-DT200) and two more sophisticated methods proposed in the literature. The Monte Carlo method and an improved first order reliability method (FORM iHLRF) were used to determine the structural reliability of an RC beam with externally bonded FRP. The results show the effects of the different mechanical methods in the reliability indices of the strengthened RC beam. The performance function related to FRP rupture presented a much higher reliability index than the other failure function related to FRP debonding for all four methods. A reliability-based design optimization was also performed to measure the effects of the assumptions and uncertainties associated with each method regarding the design variable (width of the reinforcement) for the same target reliability. The most conservative methods were the standards (ACI 440.2R and CNR-DT200), leading to a wider FRP reinforcement than the ones estimated by the other methods for the same reliability safe level design.

Strengthening RC beams using externally bonded CFRP sheets with end self-locking

When laminates of fiber reinforced polymer (FRP) are just bonded on the substrate of reinforced concrete (RC) members for strengthening, debonding failure often happens prematurely and suddenly on the FRP-concrete joints. It is unbeneficial to efficient employment of FRP and reliable service of the structures. This paper introduces a mixed anchoring technique for FRP sheets that combines external bonding (EB) and a novel type of end anchorage. FRP sheets are self-locked at ends by wrapping about a slotted plate in a specified way. Experiments on four concrete beams demonstrated that adding end self-locking to EB can effectively solve the serious problems of usual debonding. End debonding was simply prohibited and intermediate crack debonding was substantially restricted despite occurrence. As a result, not only ultimate strength but also failure ductility of the strengthened specimens was greatly enhanced. The final failure featured by either FRP rupture or concrete crush regardless of debonding degree. Finite element models are then established to simulate the responses of the strengthened beams with hybrid anchored FRP. The numerical results show good agreements with the test observations including debonding process and failure modes. It proves capability and accuracy of the modeling as a useful tool for further research.

Assessment of plate-end debonding design provisions for RC beams strengthened with FRP

Despite the enhancement in the flexural capacity of reinforced concrete (RC) members externally strengthened with fiber reinforced polymer (FRP) composites, debonding of the FRP from the concrete substrate at its ends is a major concern. This premature failure mostly occurs at a low fraction of the FRP rupture strain, thus compromises the effectiveness of FRP-strengthening. This paper presents a review on plate-end (PE) debonding as a critical failure mode in FRP-strengthened beams. The available models for predicting this mode of failure are also presented and assessed against experimental database established from previous studies. The precautions recommended by the relevant design codes to prevent PE debonding are also discussed and assessed. Based on the assessment, several conclusions are emphasized, including the inaccuracy in predictions of PE debonding given by most available models when compared with the experimental database and the inconsistency among these models. The assessment also revealed that the precautions recommended by most of the design codes are not adequate to prevent PE debonding.

Fused structures for safer and more economical constructions

Safety margin and construction costs are two conflicting goals for a structure. By providing a fuse in a structure that is triggered at a certain level of over-loading, further increase of loading is prohibited and failure of the structure is changed to a safer mode. As overloading is controlled and a safer failure mode is enforced, a fused structure requires a smaller safety factor thus leading to more economical construction without compromising safety. The use of a fuse will also facilitate safer use of advanced construction materials such as fiber-reinforced polymer (FRP) composites. In this case, a fuse can transfer the sudden and dangerous failure mode associated with brittle FRP debonding or rupture to a safe and ductile failure mode at the fuse location. This paper introduces a new type of fused structure as well as an associated design philosophy and approach, in addition to examples of engineering applications.

An improved wrapping scheme of axially loaded fiber-reinforced polymer confined concrete columns

Columns failed near the mid-zone were commonly found in practical engineering when subjected to an increasing compression load caused by the vertical ground motion during an earthquake, indicating that more confinement may be necessary at the mid-zone. Fiber-reinforced polymer (FRP) materials have been widely used to strengthen the columns. Different wrapping schemes, including full, partial, and nonuniform wrap, have been proposed. Generally, FRP-confined concrete stub columns using the existing wrapping schemes failed by the rupture of FRP at the middle zone, indicating the middle zone of the columns were not well confined by using the existing wrapping schemes. A new wrapping scheme with more FRP sheets applied in the middle zone is proposed. Experimental tests with a total of 28 specimens were conducted to evaluate the performance of different wrapping schemes, based on which an arrangement way that the applied FRP materials decrease from the middle zone to the end is recommended. The results suggest FRP materials along the height of a column can be more efficiently utilized by using the recommended wrapping scheme. Additionally, compared with the specimens using the existing wrapping schemes with the same amount of FRP materials, the recommended wrapping scheme significantly improves the strength and ductile behavior of columns.