Journal of Composites for Construction

Using large rupture strain (LRS) fiber-reinforced polymer (FRP) composites as confining material has become increasingly prominent in structural repair or retrofitting, owing to their advantageous high deformation capacity. Economic and rational usage of LRS FRP relies on displacement-based design, which requires calculation of the ultimate deformation of a member. However, prediction of the ultimate strain of LRS FRP–confined concrete is more complex and can be more inaccurate than prediction of strength, especially for structural elements under large deformation or severe damage conditions. This study proposes a unified ultimate strain model for LRS FRP–confined concrete based on an energy balance method. A unified expression form is derived using this method, providing an ultimate strain model with no restrictions on column cross section, in terms of circular, square, or oblong columns. The proposed ultimate strain model has a wider application and a better performance than other models. Furthermore, according to this paper’s updated database, the characteristic points on the whole stress–strain curve can also be accurately determined. Using the new ultimate strain model for LRS FRP–confined concrete and its characteristic points, the whole entire stress–strain curve of LRS FRP–confined concrete is accurately derived.

Steel–basalt fiber composite bars (SBFCBs) exhibit excellent strength, elastic modulus, toughness, corrosion resistance, and low cost. Understanding the bond performance between SBFCBs and concrete is important for evaluating the mechanical behavior of SBFCB-reinforced concrete structures. In this study, the bond–slip performance of SBFCB in concrete was experimentally assessed via pullout and beam bond tests. The influence of various factors on the bond performance was discussed, and the bond mechanism between SBFCB and concrete was analyzed. The results indicate that reducing the thread pitch ratio in the SBFCB can reduce slippage at the postpeak bonding stress–slip curve. The bond strength of the SBFCB was significantly improved by sandblasting. Longer bond lengths correspond to smaller average bond strengths in SBFCB. The load corresponding to the maximum bond strength of a specimen with a bond length of 10d was determined as the ultimate load value for the SBFCB. An increase in the SBFCB diameter had a negative impact on the bond strength. Moreover, an increase in the concrete cover thickness was conducive to improving the bond strength; if the thickness of the concrete cover was sufficiently increased, failure occurred owing to SBFCB tension rather than bonding. Based on the test results and the existing bond–slip model, a simple bond–slip constitutive model of the SBFCB embedded in concrete was proposed to simulate the pullout process of the SBFCB. Subsequently, the established bond–slip model can be used to analyze the mechanical performance of SBFCB-reinforced concrete structures.

This paper presents details of an experimental program evaluating the behavior of six half-scale glass fiber–reinforced polymer (GFRP) reinforced concrete beam–column precast members connected together through pocket connections, which are subjected to cyclic loading. The novel beam–column connection was constructed by incorporating either epoxy resin or tensioned or untensioned GFRP rock bolts in conjunction with different-sized pocket connections. The effects of an additional connection bar between the column and beam components in the connection, as well as the confinement of the concrete around the pocket region, were also investigated. An innovative test setup was designed so that the beam–column joint could rotate without restraint provided by the supports. All specimens were tested under an incrementally increasing cyclic load. The load-carrying capacity, deformational behavior, failure modes, energy dissipation, and hysteretic damping were all recorded and evaluated. All specimens failed as a result of column failure within the pocket connection region. This was attributed to the relative rotational flexibility of the column with respect to the beam, owing to the low elasticity of the epoxy resin used in the pocket region, and hence the stress concentration at the column ends within the pocket area. According to the results, a pocket connection containing GFRP reinforcement providing confinement around the embedded area yielded the highest capacity, ductility, and energy dissipation under cyclic loading. The connection containing a GFRP bolt, regardless of whether or not the bolt was prestressed, did not significantly improve the performance of the connection. The findings presented here can be used for the design of precast elements reinforced with GFRP bars. Of particular relevance is application to jetties and other offshore concrete infrastructure where steel reinforcement (because of corrosion issues) needs to be replaced with GFRP reinforcement.

As emerging high-performance concrete, the engineered cementitious composite (ECC) has demonstrated excellent application potential in civil engineering. With the wide application of ECC, it not only excels in the tension state and the structural elements but also in the more complex stress state of nonuniform confinement. For a reliable and economic ECC element design, understanding the dilation behavior of ECC is crucial under complicated stress conditions. This paper presents an experimental investigation and a detailed discussion of the ECC dilation characteristics under different confinement rigidities. The authors evaluate the effects of column parameters, such as different types of fiber-reinforced polymer (FRP) composites, confinement levels, and cross-sectional shapes. Test results indicate that the ECC dilation amplitude (secant dilation) under FRP confinement is less than that of concrete due to fiber bridge effects within ECC. However, the maximum dilation rate (tangent dilation ratio) shows an opposite trend. Based on the data analysis in this study, a new lateral strain-to-axial strain model was proposed, which can predict the dilation behavior of FRP-confined ECC with nonuniform confining pressure. The proposed model not only accurately captures the dilation process of FRP-confined ECC but also precisely predicts its ultimate strain. In addition, the existing peak strength and ultimate strength models were also evaluated by the ECC test results. The comparison indicates that the strength models for concrete also apply to FRP-confined ECC when the ultimate hoop-confining stress is accurately determined.

This paper presents an experimental study on the seismic behavior of polyethylene naphthalate (PEN) fiber–reinforced polymer (FRP)-jacketed circular reinforced-concrete (RC) columns. A total of seven specimens were tested under constant axial load and cyclic lateral load. The key parameters studied were the thickness (one, two, and three layers) and type (PEN FRP and CFRP) of FRP jacket. Test results indicated that the control column failed by buckling of the longitudinal reinforcement and shortage of ductility, while concrete spalling and bar buckling were effectively inhibited by the application of external FRP jacket. It is also observed that PEN FRP-jacketed specimens had more additional strain capacity compared with CFRP-jacketed specimens at the final condition. The additional strain capacity can serve as a safety reserve for structures and make PEN FRP more suitable for strengthening large or noncircular columns. Furthermore, it is found that 1-ply PEN FRP and 1-ply CFRP had a similar strengthening effect and thus the design of PEN FRP-strengthened column can simply refer to the design method of CFRP-strengthened columns in current codes. Different FRP thickness and types had marginal impact on the hysteretic curves of the specimens, which was attributed to the low axial load ratio (0.15) and high slenderness ratio (5.25) adopted in this paper. Finally, based on a cyclic stress–strain model for longitudinal reinforcement, including buckling effect, developed by the authors in a previous study, the test columns were simulated by the Open System for Earthquake Engineering Simulation (OpenSee)s to achieve an in-depth understanding of the experimental findings and associated strengthening mechanisms. Further parametric analyses showed that considering bar buckling played a significant role in accurately predicting the hysteretic response of FRP-jacketed columns.

This study evaluates the effectiveness of externally bonded small-patch ultrahigh-modulus (UHM) carbon fiber–reinforced polymer (CFRP) plates of 460 GPa modulus in extending fatigue life and slowing crack propagation in steel plates with simulated fatigue cracks. The study investigates a range of very short bond lengths for applications where bonding space may be limited or accessibility restricted, together with the effect of single- versus double-sided application, on fatigue performance. It also compares short UHM CFRP plates with similar length normal modulus (NM) (165 GPa) CFRP plates with regard to extending fatigue life and reducing stress concentration at the crack tip. Distributed fiber-optic sensors (DFOS) and digital-image correlation (DIC) are used to capture the full strain field and track crack growth. Results showed that fatigue life was increased by up to 2.0 and 2.34 times for single- and double-sided UHM CFRP repairs. As bond length increased from 25 to 100 mm, fatigue life increased from 1.36 to 2.0. UHM CFRP more effectively reduced stress concentration at the crack tip, by 60% compared with 37% for NM CFRP, indicating that it has the potential for superior fatigue life gains, relative to NM CFRP if the necessary bond length to prevent or delay debonding is provided. As debonding failure governed in this study, NM CFRP plates achieved comparable fatigue life extension. DIC tracking of crack growth matched the traditional “beach marking” technique with less than 6% difference.

Abstract

Estimating the shear strength of a fiber-reinforced polymer (FRP)–reinforced-concrete (RC) beam is a complex task that depends on multiple design variables. The use of FRP bars has emerged as a promising alternative to diminish the corrosion problems that are associated with steel reinforcement in adverse environments; however, an accurate and reliable method of shear strength prediction is needed to ensure the economical use of materials and robust designs. Several optimized design equations are available in the literature; however, when utilizing these equations a substantial difference is observed between the predicted outcome (V_pred) and the experimental shear strength (V_exp) result. Therefore, this paper presented a novel approach toward implementing machine learning (ML) algorithms to accurately estimate the shear strength of FRP–RC beams. A large database that consisted of 302 shear test results on FRP-reinforced slender concrete beams without stirrup was collected from the literature to formulate the most efficient prediction model. The performance of each ML algorithm model was compared with the existing design provisions and models. The model interpretation was performed through feature importance analysis to explain the model output compared with a black box. The proposed data-driven ML models demonstrated a high level of accuracy and excellent performance and were superior to the existing shear strength models. In addition, a simple graphical user interface (GUI) was developed to aid practicing engineers when estimating shear strength without the need for complicated design procedures.

Practical Applications

The shear strength of FRP–RC beams is calculated using various design codes and guidelines that are heuristically developed based on previous test results. In general, the developed equations are either mechanics-based or empirical. However, this paper demonstrated that data-driven ML algorithms could generate a more reliable and appropriate prediction of the shear strength of FRP–RC beams. Furthermore, as the database increases, it could be automatically updated, which would result in more accurate and reliable results. Designers and practitioners could conveniently use the developed algorithms for the reliable and quick prediction of the shear strength of FRP–RC beams. In addition, the developed GUI is innovative and user-friendly. It allows users to determine the design shear strength without referring to an existing code by employing ML in conjunction with a large, reliable, and authenticated database to ensure accuracy. This could be important for the structural engineering community when assessing the shear capacity of existing FRP–RC beams.

Abstract

In recent decades, the number of applications of fiber-reinforced polymer (FRP) reinforcement for concrete has significantly expanded. This fact is mainly due to the FRP reinforcement cost competitiveness, the increasing availability of design provisions, and due to the advantageous physical-mechanical and chemical properties of this composite material, which open up new possibilities for the design and implementation of extremely durable elements. Currently, the most commonly used types of reinforcement bars are those containing glass FRP (GFRP) or basalt FRP fibers, which is mainly the result of their favorable price and high resistance to aggressive environments. The use of composites in construction is wide-ranging: it is possible to apply FRP bars not only in the design and strengthening of concrete structures but also in the installation of shear dowels in concrete pavement, as rock bolts or as anchors for overhanging facade components. In the case of the design of load-bearing elements subjected to a combination of tensile and shear force, it is necessary to quantify their shear resistance and concisely describe the effect of the interaction of the tensile and shear force on the load-bearing capacity of the reinforcing element. This is a broadly addressed area as regards composite laminates and fabrics, but when it comes to FRP bars, there are very few available experimental results. For that reason, this research deals with the experimental testing and quantification of the influence of the interaction of normal and shear force. The behavior of GFRP bars from two different manufacturers, with three different diameters, different surface treatments, and mechanical characteristics, was experimentally verified. The findings are presented, a material failure curve is compiled, and the results are compared with those predicted according to the available relationship for composite laminates and von Mises theory.

Practical Applications

The presented research was driven foremost by industry demand concerning prestressed fiber-reinforced polymer (FRP) rock bolts. In situations where such bolts are used, the slippage and displacement of parts of rocks can be expected, and consequently, the creation of a shear plane in the prestressed anchor occurs. However, there are no existing methods for determining the load-bearing capacity of such loaded FRP bars. This paper aims to determine the short-term behavior of specimens under the combined action of tensile and shear forces (failure envelope) and to compare their load-bearing capacity with available relationships for steel and composite laminates.

Concrete-filled fiber-reinforced polymer (FRP) tubes (CFFTs) are an emerging and attractive form of column for new constructions. Such a column consists of outer filament-wound FRP tubes that are filled with plain or steel-reinforced concrete. The fibers in the filament-wound FRP tube are predominantly in the hoop direction to confine the inner concrete, which leads to significantly enhanced strength and ductility in the confined concrete. Extensive studies have been conducted on the behavior of CFFTs that were subjected to various loading conditions, which confirmed the excellent performance of such members. As CFFTs become increasingly used in practice, there is a concern about the performance of CFFTs when the FRP tube is subjected to local damage that is caused by accidents, vandalism, or designed holes or cuts to accommodate connections with other structural components. Some studies have been carried out on the performance of CFFTs as flexural members with a locally damaged filament-wound FRP tube; however, the research on such CFFTs as columns remains limited. This paper presented the results of a comprehensive experimental program on the axial compressive behavior of CFFTs with a filament-wound FRP tube that was subjected to local tube damage. Two types of damage (i.e., holes and cuts) with different parameters were investigated. The test results showed that the compressive strength [i.e., peak stress ( $f_{\mathrm{cc}}^{\mathrm{\prime }}$)] and the corresponding axial strain (ɛ_cc) of the damaged CFFTs were significantly reduced due to the local tube damage (e.g., $f_{\mathrm{cc}}^{\mathrm{\prime }}$ reduced from 12.2% to 64.8% and the corresponding ɛ_cc reduced from 35.2% to 77.2%). Finally, an existing model for FRP-confined concrete that considered the local FRP damage was evaluated which suggested the need for the recalibration of the model or the development of a new model for CFFTs with a locally damaged filament-wound FRP tube.

A near-surface-mounted (NSM) technique using fiber-reinforced polymer (FRP) reinforcement increases the load-bearing capacity and stiffness of reinforced-concrete (RC) beams and delays the yielding moment. In those cases, the verification of serviceability limit states becomes necessary to guarantee functionality and protection of steel reinforcement. At present, there is a lack of provisions for the crack width prediction, mainly because of the scarceness of experimental data. This work presents the results of an experimental program aiming at studying the effect of different NSM reinforcement arrangements on the midspan deflection, crack spacing, and crack width of NSM FRP RC beams. One RC beam and 11 NSM FRP RC beams were tested under a four-point bending configuration up to failure. Carbon- and glass-FRP rods were used. It was found that NSM FRP reinforcement provides an effective reduction in deflection, crack width, and spacing. Larger crack formation phases were observed in all strengthened specimens. Moreover, crack width decreases with the increase of the NSM FRP reinforcement ratio. Finally, cracks at the bottom of the beam are around 11%–25% wider than at the height of the steel internal reinforcement.

This paper reports on a series of four-point bending experiments to investigate the shear capacity of reinforced concrete (RC) beams strengthened with externally bonded basalt fiber–reinforced polymer (BFRP) sheets. The experimental results show that BFRP sheets can significantly increase RC beams’ shear capacity and ductility. To analyze the fracture and mechanical behaviors of BFRP sheet–strengthened RC beams, a three-dimensional (3D) finite-element model (FEM) based on the application of cohesive elements was developed. Mixed-mode constitutive models of the BFRP–concrete interface, the concrete potential fracture surface, and the reinforcement–concrete interface were proposed. The proposed constitutive models were able to characterize the interface’s normal separation, tangential slip, and friction. A comparison of the simulation and experimental results indicates that the proposed numerical model can appropriately simulate the mechanical response, crack propagation, and crack distribution of BFRP sheet–strengthened RC beams. Finally, based on the proposed 3D FEM, a series of numerical tests were conducted to investigate the influence of key parameters (i.e., sheet elastic modulus, sheet bonding area, and sheet bonding angle) on the shear capacity of BFRP sheet–strengthened RC beams.

Concrete structures reinforced with fiber-reinforced polymer (FRP) reinforcement have been increasingly applied in civil engineering construction to improve several structural performances of bridges and buildings. However, the major weakness of these structures is that they typically suffer from poor ductility and brittle failure. An innovative mechanism called compression yielding (CY) has recently been proposed to enhance the ductility of FRP-reinforced concrete beams. In this study, the moment capacity and ductility of CY beams with T sections are analyzed based on a layered approach. The key variables in the design of a CY beam with a T section are identified and their importance is comprehensively investigated based on the elementary effects method and a parametric study. It is found that the ductility performance can be effectively improved by using a CY material with postmodulus ratio close to 0, and the moment capacity can be enhanced significantly by increasing the CY material strength. The most effective measure for simultaneously improving the moment capacity and ductility performance is to increase the CY block height.

Abstract

The application of externally bonded (EB) carbon fiber reinforced polymer (CFRP) systems for strengthening existing structures, such as RC beams, has been widely approved in the construction industry worldwide for its numerous benefits. The CFRP-to-concrete bond has a governing role in the reliability and effectiveness of EB-CFRP systems. Indeed, failure of the CFRP-to-concrete bond can lead to rupture of CFRP-strengthened structures. Hence, ongoing research into assessment of bond behavior at the CFRP-to-concrete interface helps to bring more insightful clarity to the use of EB-CFRP strengthening techniques. The aim of this study is to evaluate the bond behavior between CFRP and concrete by conducting a series of pullout tests. The parameters considered include CFRP type (sheet versus laminate), bonded length, and bonded CFRP width. The results show that using CFRP fabric sheets can contribute to higher bond load-carrying capacity and ductility than CFRP laminates. Furthermore, through the analyses of databases in the literature, a bilinear bond–slip model is proposed that takes into account the CFRP width factor. Through a comparison, it is shown that the proposed model performs well in terms of predicting the maximum local bond stress and CFRP slippage.

Practical Applications

This research was aimed at investigating the use of CFRP composites for strengthening RC structures. The complexities regarding the behavior of CFRP-strengthened RC beams and columns, especially at the CFRP-to-concrete bond, provoked the authors to conduct this experimental study. The testing program was intended to evaluate the effect of certain parameters on the bond behavior of a CFRP-to-concrete interface. In addition, an analytical study was carried out to develop a model, capable of characterizing the interfacial behavior in terms of bond shear stress and bond slip. The proposed model proved to perform well at predicting the bond–slip behavior in a validation study. Findings obtained from this research can better familiarize civil engineers with the application of EB-CFRP strengthening techniques in concrete surfaces and possibly enhance the design of such retrofitting systems in deficient real-life RC structures.

Externally bonded fiber-reinforced polymer (FRP) laminates are widely used in the retrofitting and rehabilitation of reinforced concrete (RC) columns because they can increase the axial and bending moment capacities of these columns through a confinement mechanism. The confinement produced by FRP laminates acts in addition to that exerted by the internal transverse steel, although the latter is often neglected in current design standards and guidelines. In this study, a recently developed FRP-and-steel-confined concrete constitutive model was employed to numerically investigate the axial force–bending moment interaction for FRP-confined RC columns modeled using finite-element (FE) analysis. The proposed model was first validated against experimental data available in the literature and then used to quantify, through an extensive parametric study, the effects of transverse steel confinement, FRP strength, FRP stiffness, FRP reinforcement ratio, column diameter, concrete compressive strength, and load eccentricity ratio on the strength of FRP-confined RC columns subject to combined axial compression and bending moment. It was found that the internal steel confinement can substantially enhance the strength of these columns, especially for low concrete compressive strengths, large cross sections, and small eccentricities. When design code provisions limiting concrete and FRP deformations were considered for eccentrically loaded columns, the contribution of the steel confinement increased for increasing FRP reinforcement ratio. Based on the parametric study results, this investigation proposed an extension to eccentric axial compression of two relative confinement coefficients, which were previously developed to describe the contribution of transverse steel confinement to the peak strength of FRP-confined RC columns subject to pure compression.

Damage quantification in terms of engineering demand parameters (EDPs) is a critical element of the performance-based design (PBD) approach. A widely used EDP for reinforced-concrete (RC) bridge columns is the drift ratio. This study establishes drift ratio limit states, and corresponding strengths for hybrid GFRP–steel RC circular bridge columns. The adopted reinforcement layout in this study consists of two layers of reinforcement, exterior with GFRP and interior with steel. Such coupling between the two materials in concrete bridge columns improves their corrosion resistance while maintaining their stiffness and ductility. Here, a validated fiber-based model is utilized to predict global as well as local responses of hybrid RC columns under monotonic displacement-controlled loading. A full factorial analysis was first adopted to screen parameters potentially influencing drift ratio limit states and corresponding strengths for their significance. The resulting data were then fitted to mathematical expressions using machine learning-based symbolic regression. Lateral load–deformation responses predicted based on the proposed expressions were validated against existing data from the literature. A complete example demonstrating how the proposed expressions could be utilized to design a hybrid bridge column within the context of PBD is also presented.

Abstract

Overlays consisting of welded steel-wire mesh embedded in an inorganic matrix have shown promising results in improving the flexural behavior of masonry in terms of strength, ductility, and energy dissipation. The flexural capacity of masonry strengthened with steel-wire–reinforced cementitious matrix (SWRCM) can be influenced by various factors, such as the percentage of reinforcement, strength of cementitious matrix, and masonry compressive strength. To understand the influence of these parameters, the results of past experimental studies were carefully examined, and parametric finite-element analyses were performed. The analytical equations available in the literature were used for the flexural capacity estimation of masonry reinforced with SWRCM; however, the majority of them could not provide accurate and reliable predictions. This may be due to neglecting the contribution of the cementitious matrix and debonding at the interface of the masonry substrate and composite overlay. Thus, a new equation has been proposed in this study for estimating the flexural capacity of masonry strengthened with SWRCM, which can consider the contribution of the inorganic matrix and the debonding at various interfaces through an effective tensile strain parameter. In addition, a stepwise procedure has been provided to estimate the effective tensile strain of SWRCM composite. Results of the analytical investigation showed that the proposed method can effectively provide a reliable and consistent prediction of the flexural capacity of masonry strengthened with SWRCM composites.

Practical Applications

This study provides information about the role of various parameters in influencing the flexural capacity of masonry strengthened with steel-wire–reinforced cementitious matrix (SWRCM). To estimate the flexural strength of masonry reinforced with SWRCM, there is a lack of analytical methodology in the existing literature. Therefore, this study evaluated the suitability or reliability of existing equations, originally developed for fabric-reinforced composite, in predicting the flexural capacity of SWRCM-strengthened masonry. Further, this study proposed an equation to predict the flexural capacity of SWRCM-strengthened masonry. To address the contribution of cementitious matrix and debonding failure, an effective strain parameter was introduced in the proposed equation, and to determine its value, a step-wise test methodology was described in this study. In addition, an empirical equation was proposed to calculate the value of effective strain. This equation may be helpful when it is not possible to perform the material characterization tests for SWRCM. The developed equation along with the effective strain parameter provided a reliable prediction of flexural capacity for masonry specimens strengthened with different types of SWRCMs. The proposed analytical method may help engineers in designing the SWRCM strengthening for vulnerable masonry structures.

A three-dimensional numerical model was established to investigate the impact resistance of concrete shear walls reinforced with fiber-reinforced polymer (FRP) bars, considering the strain rate effect of FRP reinforcement and concrete materials. After validating the numerical model, the failure mechanism of concrete shear walls reinforced with glass fiber–reinforced polymer (GFRP) bars under impact load was studied. The influence of impact velocity and axial load ratio on the impact resistance of GFRP-reinforced concrete shear walls was discussed. The results showed that GFRP-reinforced concrete walls have similar behavior to conventional reinforced concrete walls under impact loadings. The former experienced more considerable deformation due to the lower elastic modulus of GFRP bars. The peak and residual displacement at the center of the wall increased linearly with the impact energy. In addition, the peak value, plateau value, impulse, and duration of impact force grew linearly with respect to impact velocity. The proportion of energy absorbed by concrete increased in the cases of larger impact velocity. From the perspective of the internal force envelope along the wall height, the dangerous sections under impact were located at both ends of the wall under axial load. The peak value of the internal force improved with an increase of the axial load ratio. When the axial load ratio was between 0.3 and 0.4, the impact force of the wall reached the largest, and the minimum deformation occurs, indicating the best impact resistance of the shear walls. As the axial load ratio increased from 0.1 to 0.5, the total energy consumption increased from 68% to 89%, among which the external force work is 57 times that of the 0.1 axial load ratio, aggravating the failure of walls.

It has been proved that external bonding of fiber-reinforced polymer (FRP) composite materials with epoxy interlocking (EB-FRP-EI) enhancement could significantly improve the strength of FRP-to-concrete joints from experimental studies. However, there still exists a barrier to comprehensively implementing the EB-FRP-EI method in practical applications, owing to the lack of full reliability-based design guidelines with consideration of the uncertainty raised from materials, model errors, and loading. In this study, a numerical function of bond strength for EB-FRP-EI was derived by taking both the adhesion effect and mechanism doweling enhancement into account. The reliability analysis of the EB-FRP-EI method was conducted by utilizing the first-order reliability method (FORM). Corresponding to the required reliability index, two-parameter (groove depth and number) reliability-based design was performed for 35 (7 × 5) FRP-to-concrete joints in total. The effects of design and modeling parameters, including depth of grooves, number of grooves, thickness of FRP, width of FRP, and strength of concrete, on reliability performance of the bond strength of FRP-to-concrete joints with epoxy interlocking enhancement are presented and discussed. As a result, this study provides suggestions for the proper design of FRP-to-concrete joints with epoxy enhancement based on these parameters.

This paper evaluates the seismic behavior of eight one-third-scale concrete bridge piers reinforced with various configurations of steel or glass fiber–reinforced polymer (GFRP) bars. Each specimen was tested under a constant axial gravity load, combined with reversed quasistatic cyclic lateral loading. The behavior of the piers was assessed and compared in terms of strength, stiffness, deformability, energy dissipation, and damage. The results indicate that well-detailed hybrid configurations with steel longitudinal bars and GFRP spirals offer a ductile seismic response with reduced postpeak strength degradation. The GFRP spirals were effective in confining the concrete core and restraining longitudinal bar buckling. Piers reinforced with GFRP longitudinal and transverse bars exhibit a stable and deformable seismic response with little residual displacement or strength degradation. However, this behavior was accompanied by a reduction in effective stiffness exceeding 40% and approximately half the hysteretic energy dissipation at an equivalent drift level. All piers reinforced with GFRP bars or spirals exceeded lateral drift requirements set by North American codes.

The relatively low shear strength of carbon fiber-reinforced polymers (CFRPs) makes it difficult to anchor CFRP tendons. Although many anchorages with CFRP tendons have been developed, few studies have been conducted on composite anchorages with multi-CFRP tendons. In this study, four groups of new mechanical clamping–bonding composite anchorages with multi-CFRP tendons were designed, and the stress of each component of the anchorage was analyzed to reveal the force transmission mechanism of the anchorage. Moreover, the short-term performance of the anchorages was experimentally investigated. The key parameters, including the elastic modulus of the bonding medium, preloading force, cone angle, and bond length, were further analyzed using the finite-element method. The results showed that the composite anchorage reliably anchored multiple CFRP tendons, and the efficiency coefficients of the four anchorages were greater than 0.95. The suggested minimum bond length was approximately 35 times the diameter of the CFRP tendon when anchoring fewer than five tendons. Finally, a sufficient preloading force could effectively reduce the initial slip, whereas increasing the cone angle and elastic modulus could reduce the final slip.

This paper reports on the feasibility of using fabric-reinforced cementitious matrix (FRCM) systems to strengthen two-span reinforced concrete (RC) beams that are structurally deficient in their sagging regions. In addition to one unstrengthened control beam, nine beams strengthened either symmetrically or asymmetrically with polyparaphenylene benzobisoxazole (PBOFRCM), carbon (CFRCM), and carbon fiber–reinforced polymer (CFRP) sheets were tested under a five-point load configuration. Test results showed that increasing the strengthening ratio resulted in significant increases in the yielding and load-carrying capacity of the beams. Beams symmetrically strengthened with PBOFRCM showed high ductility indices ranging between 100% and 121% of that of the control beam, whereas those strengthened with CFRCM and CFRP showed ductility indices of 45% and 34% of that of the control beam, respectively. Moreover, beams symmetrically strengthened with PBOFRCM systems encountered moment redistribution ratios between 42% and 82% of that of the control beam compared with 10% and 9% only for those strengthened with CFRCM and CFRP systems, respectively. The asymmetric strengthening configuration in which FRCM systems were used along with CFRP sheets proved to be an efficient method to enhance the ductility and moment redistribution capacity of the strengthened beams. Analytically, the rigid-body-rotation approach was modified to predict the moments and curvatures at the plastic hinges of the strengthened sections. The predicted moments and curvatures showed a notable agreement with the experimental values.

In this study, a total of 10 steel and glass fiber–reinforced polymer (GFRP) bar–reinforced normal strength concrete (NSC) specimens with a square cross section of 200 mm × 200 mm were experimentally tested up to failure under different loading conditions. Out of the 10 specimens, 8 specimens had a height of 800 mm and were tested as columns under concentric and eccentric axial loads. The remaining two specimens had a length of 1,500 mm and were tested as beams under four-point bending. The tested specimens were utilized to investigate the efficiency of carbon fiber–reinforced polymer (CFRP) strip ties (CSTs) in transversely confining NSC specimens. Two configurations of CSTs were used: a square (S) configuration and a square overlapping square (SS) configuration. The experimental results indicated that the peak axial load and ductility of the concentrically loaded GFRP bar–reinforced concrete specimens were lower than those of steel bar–reinforced specimens. The peak axial load and ductility of the concentrically loaded GFRP bar–reinforced concrete specimens with SS configuration were about 49% and 100%, respectively, higher than those of GFRP bar–reinforced concrete specimens with S configuration. Also, the GFRP bar–reinforced concrete specimens tested under eccentric loading and four-point bending achieved higher peak axial loads, flexural loads, and bending moments at the second peak loads than the corresponding steel bar–reinforced specimens.

The American Concrete Institute has developed a design standard for glass fiber–reinforced polymer (GFRP) RC members, dependent to their standard for steel-reinforced structural concrete. Design examples conforming to code language have been developed and their solutions examined to understand the impacts that code requirements have on the design of GFRP-RC members. The impacts include selecting member dimensions and reinforcement on the basis of serviceability requirements, rather than strength, and the related detailing issues involving bar cutoff points. As the design of GFRP-RC members is typically controlled by serviceability requirements, some reinforcement may be provided to satisfy deflection requirements. Cutoff points for such bars must be located differently than for steel bars, where the cutoff point is determined by strength requirements. A proposed method locates cutoffs by calculating the resulting maximum deflections as the cutoff point is varied. A second, approximate, approach locates cutoffs at points where continuing bars provide the same value for effective moment of inertia as that available from all bars at the critical section. The second method results in longer bar lengths but is more easily applied. Shear and crack control requirements should also be checked at cutoff locations.