Journal of Composites for Construction

Textile-reinforced mortar (TRM) has proved to be a valid engineering material for the upgrading and retrofitting of existing masonry and concrete structures subject to seismic actions, because it can be applied in thin layers that can increase load-bearing capacity while providing significant durability. However, characterization activities at the composite scale have mainly focused on the material’s monotonic behavior and few studies have so far addressed the material’s performance in the presence of cyclic actions. In this work, we set ourselves the goal of investigating the uniaxial tensile behavior of a series of cement-based matrix composites reinforced with alkali-resistant (AR) glass fabrics, also considering the possible inclusion of short dispersed polyvinyl alcohol (PVA) fibers. Quantification of the stiffness degradation accumulated by the composites during unloading–reloading cycles allowed us to evaluate the damage evolution in uniaxial tension through data interpolation, providing analytical formulations that may represent a benchmark for the validation of advanced nonlinear simulations.

Abstract

The paper presents the results of research on a nearly full-scale, 1-story reinforced-concrete (RC) spatial frame structure with masonry infill walls tested on a shake table. The experiment was conducted in four phases to investigate the in-plane and out-of-plane responses of the infill walls of the specimen. The use of a digital image correlation (DIC) technique with noncommercial analysis system allowed the computation of principal strains for the infill. Two methods of infill-RC frame protection using polyurethane resin (PU) flexible joints (PUFJ) at the RC frame-infill connection and an external innovative fiber-reinforced PU (FRPU) repair system were considered in the research. The test results indicated that the in-plane and out-of-plane infill performance was enhanced under seismic excitations. The PUFJs at the interface of the frame and infill walls helped the infills to withstand dynamic excitation of high intensity with repairable damage. Furthermore, the externally applied glass FRPU repair system efficiently protected the damaged masonry infills against collapse under out-of-plane excitation while restoring a significant portion of their in-plane stiffness. The variable contributions of the RC frame and of the brick infills when protected with innovative joints are evaluated through three-dimensional finite-element models.

Practical Applications

Externally bonded fiber-reinforced PU composite is prefabricated or constructed on-site repair and strengthening solution, consisting of strengthening fibers and flexible polyurethane matrix. It is capable of carrying high loads and high deformations simultaneously and allows for reducing of stress concentrations and redistributing them over large bonding area, what results in higher load capacity of the composite strengthening systems. This innovative composite solution is dedicated to structures made of brittle materials (concrete, masonry) located in seismic areas. Flexible polyurethane matrix allows working with even low-strength fibers and low-strength brittle substrates, introducing greater strength, ductility, and load-bearing capacity, making it safer in exploitation. This composite strengthening system was examined as emergency strengthening of infill walls damaged by vibrations on a shake table. Repeated seismic excitations of high intensity were unable to cause collapse of the infill walls protected by this innovative composite system, neither in in-plane nor in out-of-plane modes. The tested building specimen of natural scale, protected by the flexible composite system, survived many seismic excitations remaining in good structural shape. This paper presents results of dynamic tests, proving practical efficiency of the composite system examined in more dangerous conditions than are present during strong earthquakes.

Carbon fiber–reinforced polymer (CFRP) tendons are gaining significant interest in the construction industry owing to their high corrosion resistance. Full-depth precast concrete deck panels (PCDPs) with connections provide advantages for accelerating the construction of superstructures, such as minimizing traffic interruption and improving construction quality. The influences of the connection configuration on the mechanical properties, convenience of construction, and economic cost of PCDPs are the focus issues to be concerned. The poor durability of connection materials also hinders the practical application of full-depth PCDPs. In this paper, a novel high-performance connection for PCDPs was proposed, taking ultrahigh-performance concrete (UHPC) and CFRP strand as grout material and post-tensioned tendon, respectively. The high-performance connection has high strength and durability. Four-point bending experiments were conducted to investigate the flexural performance of PCDPs with the proposed novel connection, including failure mode, moment–deflection curve, capacity, ductility, and working mechanism. Moreover, the numerical simulations were carried out to evaluate the impacts of parameters on the flexural capacity in Abaqus software. An improved analytical model was put forward to predict the balanced CFRP tendon ratio and flexural capacity of PCDPs. The results show that it is ductile-control for the failure mode of PCDPs with high-performance connections. The flexural capacity is significantly improved with the increased quantity of welded studs, initial tendon stress, concrete strength, and anchorage spacing. The proposed connections could effectively promote the behavior and durability of PCDPs.

The effectiveness of near-surface mounted glass fiber–reinforced polymer (NSM GFRP) retrofitting of reinforced concrete (RC) beams after exposure to fire is investigated in this study both experimentally and analytically. Experiments were performed on nine RC beams: one beam was not exposed to fire (control specimen) and eight beams were divided into two groups exposed to fire for 30 and 60 min. In each group, one beam was not retrofitted, whereas the other three beams were retrofitted using NSM GFRP. After retrofitting, all beams were loaded until failure. The experimental results confirmed that the retrofitting technique effectively recovered the strengths of postfire RC beams. The failure mode of the GFRP retrofitted beams was the peeling-off of concrete cover, whereas that of the control and unretrofitted postfire beams was flexural failure via the yielding of tension steel. The NSM GFRP retrofitting fully recovered or significantly increased the yield and ultimate strengths of postfire RC beams by up to 39%. The yield deflection capacity of the NSM GFRP retrofitted postfire beams was much higher than that of the control beam; however, the ultimate deflection capacity of these beams significantly decreased. Consequently, the GFRP retrofitted postfire beams were of low ductility because of the peeling-off of the concrete cover. NSM GFRP retrofitting slightly improved but did not completely recover the yield stiffness reduced by fire, whereas it increased the plastic stiffness significantly by up to threefold. An analytical model for estimating the yield moment of postfire RC beams without/with NSM GFRP retrofitting was proposed, considering the very limited information, for example, fire duration obtained from actual fire events. The practicality and reasonable accuracy of the proposed model render it beneficial for structural engineers.

The architectural beauty of curved structures is recognized worldwide. Owing to their balanced form, vaults, domes, and arches were largely adopted over the last centuries. Currently, the erection of new curved masonry structures is dramatically reduced. However, strengthening existing arches is often required to prevent their collapse under static or seismic force. Present limitations regarding such constructions include the antiquated and expensive erection technique employed for curved members. Moreover, the assembly of provisional supporting structures (scaffolding) is generally time- and cost-consuming. Accordingly, the following research provides an innovative construction method that focuses on overcoming the drawbacks of the scaffolding-based approach. A fast lift-up technique was developed to reduce the time and costs of traditional construction techniques. Specifically, the required number of blocks that constitute the arch in this study was aligned side by side on the floor and then connected using a bonded strip of composite material (i.e., FRP—fiber-reinforced polymer). The middle block was then lifted. Thus, each corresponding block could be rotated around the contact point with the adjacent block. When all blocks left the floor, an arch shape was achieved. To validate the proposed method in terms of mechanical performance, an experiment was conducted, as reported herein. A traditional masonry arch built using scaffolding was tested for comparison, and two types of reinforced arches were tested until failure. The first was traditionally built and then reinforced, whereas the second was built using the proposed innovative technique. The specimens were instrumented and tested under a centered or eccentric vertical point load. In all cases, the composite application prevented failure of the hinged joints, as is typical of unreinforced arches, resulting in significantly increased loadbearing capacity, which registered scatters of |11|% and |28|% for the centered and eccentric loads, respectively, when comparing the traditional reinforced arch with the innovative solution.

Coastal bridge piers are prone to corrosion attack owing to their exposure to marine environments, particularly in the splash and tidal zone, which is rich in chloride, oxygen, and moisture. Severe corrosion in this area results in the transfer of plastic hinges and evidently impairs the structural performance under seismic loading. Previous seismic retrofitting typically focused on the area of the pier end with the greatest bending moment. However, the location of the splash and tidal zone varies with the change in season and is generally not in the pier end. This study investigated for the first time the seismic retrofit of such piers using fiber-reinforced polymer (FRP) and engineered cementitious composite (ECC), where the middle part of the pier subjected to NaCl solution corrosion was simulated as the splash and tidal zone. Reversed cyclic loading tests of nine bridge piers with various corrosion rates, FRP types, and retrofit areas were performed. The seismic behaviors in terms of failure mode, crack pattern, load-carrying capacity, ductility, energy dissipation capacity, and stiffness degradation were compared and discussed. The experimental results of mildly corroded specimens indicated that seismic retrofitting with combined FRP and ECC significantly improved the seismic performance of bridge piers. The retrofitted specimen exhibited an even higher ductility and energy dissipation capacity than the noncorroded specimen. For severely corroded piers, the plastic hinge was transferred from the pier end to the corroded area and then transferred back to the pier end after retrofitting. The seismic performance of the specimens retrofitted from the corroded area to the foundation was better than that of the piers retrofitted only in the corroded area.

The compressive behavior of fiber-reinforced polymer (FRP)-confined concrete columns with a noncircular cross section has been investigated through extensive experimental, analytical, and numerical research, but a unified theoretical/numerical approach that can accurately predict both their section-average behavior and local concrete behavior is not yet available. In noncircular columns under axial compression, the concrete is typically under a nonuniform stress state of three-dimensional (3D) compression, with the lateral compressive stresses being the reactive stresses from the confining device (i.e., passive confinement). The authors of the present paper recently developed a plasticity constitutive model for concrete under general 3D compressive stresses, which possesses a potential surface with an evolutionary deviatoric trace that can accurately capture the results of existing compression tests of concrete cubes under nonuniform, passive confinement. This paper explores the application and capability of this evolutionary potential-surface trace (EPT) plasticity constitutive model in finite-element (FE) analysis of FRP-confined square, rectangular, and elliptical plain-concrete columns under concentric compression. The section-average behavior of all the selected noncircular columns predicted by these FE analyses was close to the existing experimental data. The numerical results obtained with the EPT plasticity constitutive model were then examined in detail to achieve an improved understanding of local concrete behavior in FRP-confined noncircular columns.

Abstract

Fabric-reinforced cementitious matrix (FRCM) composites have been widely studied as they constitute an alternative solution to fiber-reinforced polymer (FRP) retrofitting solutions for steel-reinforced concrete (RC) members. This study investigated the punching shear behavior of RC slabs strengthened with FRCM composites. Different tests were first performed to determine the tensile behavior of the FRCM and the interfacial bond behavior between the FRCM and concrete substrates. These tests were used as input parameters for a three-dimensional (3D) finite-element model (FEM) for RC slabs strengthened with the FRCM under shear. Subsequently, one reference slab and two strengthened slab specimens with dimensions of 1,600 mm × 1,600 mm × 100 mm were tested under punching shear. The test results demonstrate the effectiveness of FRCM strengthening under punching shear. An automation parameter calibration process was developed to identify the input parameters of Mazars’ concrete behavior law used in the 3D FEM model. The results of the numerical investigation can predict the punching shear behavior of reinforced concrete slabs with reasonable accuracy.

Practical Applications

There are relatively limited studies conducted on the two-way RC slabs compared with those related to RC beams, walls, or one-way slabs strengthened with fabric-reinforced cementitious matrix (FRCM) composites. The test results on the tensile behavior of the FRCM, the failure mode, and the effectiveness of the strengthening system could be referred to and consulted in future research on this aspect. A nonlinear finite-element method considering a macroscopic approach for the FRCM layer was performed to predict the behavior of RC slabs. A coupling MATLAB-Cast3M process using the fmincon function on Matlab was developed to calibrate the numerical model’s input parameters. This automation process can be used for other research and engineering applications as it is easy to implement on Matlab or Python. A parametric study was conducted to determine the effects of four factors on the shear strength and ductility of the two-way slabs, namely concrete tensile strength, concrete residual tensile strength, slab thickness, and the number of FRCM layers. Other researchers could use these results for experimental design or numerical simulation processes. Based on the experimental results, it was possible to show that the activation of the dowel effect mechanism can increase the bearing capacity and potentially provide ductility. On this aspect, a more substantial experiment should be conducted.

Self-drilling screws provide an efficient and cost-effective way of joining lightweight structural members. In this work, the performance of self-drilling screw connections for fiber-reinforced polymer (FRP) structural members is investigated, for use in joining panels or plates to square hollow sections (SHSs). To investigate the resistance to pullout loads, tensile tests were conducted on connection specimens consisting of an FRP plate joined to an FRP SHS at a right angle. The specimens were prepared in five configurations, with differences in pultrusion directions of the FRP plate, screw gauge size, and coarseness of the screw threads. The specimens having fibers oriented transversely in the FRP plate exhibited a flexural failure of the plate and the lowest connection strength. The specimens having fibers oriented longitudinally in the FRP plate failed by the screw being pulled out from the FRP SHS profiles; shearing out of the thread in the screw hole. An increase in screw gauge size and thread coarseness was found to be beneficial to the connection strength. Further analysis was carried out to estimate the initial stiffness and the connection strength, by finite-element and analytical modeling, respectively. In addition, these analyses are able to correlate the average shear stress at failure of the connection specimens to the screw gauge size, thread coarseness, and effective contact area of the screws.

The bond at the interface between concrete and the surface of a glass fiber–reinforced polymer (GFRP) bar is the most critical parameter to ensure that the strains between the GFRP bar and the surrounding concrete are compatible. To prevent bond failure, an adequate development length should be provided. This study evaluated the current recommended equations for the development length using an approach based on the regression analysis of an experimental database of results from 431 recent tests of beam bonding reported in the literature. The main objective of this work is to optimize the development length equation through a comprehensive assessment of the influencing parameters. The parameters studied in this investigation are the concrete compressive strength, concrete cover, confinement effect, bar diameter, bar location, bar surface profile, and bar tensile stress. The proposed equations were compared with the equations in current design codes.

The near-surface-mounted (NSM) fiber-reinforced polymer (FRP) strengthening technique for reinforced-concrete (RC) beams has attracted worldwide research attention and application in the past two decades. In spite of improved bond strength between the NSM FRP and concrete, compared with the externally bonded (EB) FRP method, premature debonding failure still occurs, and, hence, the efficiency of the NSM FRP intervention is limited. An intuitive means to enhance efficiency is to apply anchorage devices to the RC beam; however, the availability of viable anchorage is limited for NSM applications. A novel anchorage device is therefore presented in this paper, which is referred to as an embedded FRP anchor (EFA). The concept, manufacture, and installation of the EFAs were initially presented. The effectiveness of EFAs in NSM FRP-strengthened RC beams was then ascertained through full-scale beam tests and comparison with an NSM FRP-strengthened beam anchored with a U-jacket. Moreover, the effects of EFA parameters on the behavior of anchored beam were also investigated. The test results not only prove the high anchoring efficiency of EFA but also reveal the significant effects of EFA parameters on the failure mode, load–deflection response, and NSM FRP strain of the EFA anchored beam.

Short ultrahigh-modulus (UHM) carbon fiber–reinforced polymer (CFRP) strip panels connected through a finger joint configuration offer a convenient modular method for strengthening steel girders. Three-dimensional nonlinear finite-element (FE) analysis was conducted to characterize the interfacial and flexural behavior of strip panels. The calibrated FE model provides an efficient and economical method of evaluating different parameters related to the material properties and strengthening configuration of the UHM CFRP strip panels, for which experimental data are not available. Analysis implemented robust features, including debonding of CFRP using a mixed-mode bond–slip model, CFRP rupture, steel yielding, and concrete slab crushing. Predictions were calibrated and validated against experimental results from double lap shear tests and flexural tests of steel beams and steel–concrete composite beams. The FE model was used to investigate the effects of finger joint location, joint length, and laminate thickness. Strip panels with 300-mm-long finger joints and thicknesses of up to 2 mm equaled the strength of a continuous laminate with the same CFRP area. Both failed by CFRP rupture. At greater thicknesses, debonding occurred at lower ultimate loads than for a continuous laminate. The finger joint splice was also compared to the traditional splice plate method. The splice plate length required to achieve the same level of load transfer was longer than the finger joint length when the connection was in the maximum moment region. For a given CFRP thickness and splice plate length (or finger joint length), strip panels with finger joints provide greater load-carrying capacity.

Hollow concrete columns (HCCs) are an effective structural system for piles, electric poles, and bridge piers due to their low self-weight in conjunction with the high strength offered and reduced material use. This study investigated the behavior of concentrically loaded circular HCCs reinforced with glass fiber–reinforced polymer (GFRP) bars and spirals. Eleven hollow circular columns with outer/inner diameters of 305 and 113 mm and two solid specimens as controls were fabricated. All had a height of 1,500 mm. The investigated parameters included transverse GFRP reinforcement ratio in terms of the on-center spiral spacing and spiral diameter, configuration (spiral and hoops), and the influence of hollowness. The theoretical ultimate load-carrying capacity and the confined concrete strength of the tested hollow GFRP-reinforced concrete columns were evaluated and predicted using the available design equations and confinement models in the FRP design codes, standards, and literature. The test results indicate that either decreasing the spacing of the spiral/discrete hoops or increasing the spiral diameter could increase the ultimate carrying capacity as well as improve the confinement efficiency and ductility of HCCs.

In recent years, there has been a growing demand for a lightweight, dependable, and cost-effective construction material with low maintenance requirements and high corrosion resistance to replace steel communication towers. This paper reports on an examination of glass fiber–reinforced polymer (GFRP) as an unconventional material for the fabrication of a GFRP lightweight communication guyed tower. The study included extensive experimental testing as well as numerical modeling of a 9-m GFRP guyed communication tower. Extensive material testing was conducted to define the material properties required for modeling the guyed tower. Furthermore, the study involved the fabrication of a unique adjustable collapsible multiuse device to form the prismatic tower cells required for the tower’s fabrication. The newly designed collapsible mandrel fabricated individual cells using fiberglass matting and a hand lay-up method. The 9-m tower had a uniform constant cross section of three identical cells bonded together to form an equilateral triangle with sides of 500 mm. The tower was tested under static loading conditions using a whiffle-tree arrangement to simulate uniformly distributed wind loading. Under static loading conditions, a comprehensive experimental strain and deflection study was conducted and three critical regions on the tower were thoroughly evaluated. To simulate the structural behavior of the tower, a nonlinear finite-element model was created. The results for the finite-element model were validated by comparing them with experimental results. The structural performance of the GFRP guyed tower was accurately predicted by the finite-element model.

This paper presents a new strut-and-tie model (STM) based on provisions of ACI 318-19 and ACI 440.2R-17 for estimating the shear strength of fiber-reinforced polymer (FRP)-strengthened exterior joints. Beam–column joints are vulnerable elements in reinforced-concrete structures subjected to seismic loadings and similar extreme demands. The FRP strengthening technique offers numerous advantages for retrofitting joints in existing structures with inadequate reinforcement or confinement. The design of FRP-strengthened joints requires the development of reliable procedures, including equations to predict the shear strength of the joint. Existing literature and research on STM warrant the development of simple, reliable, and practical specifications applied to a wide range of design criteria. The proposed method involves an STM model containing horizontal and vertical mechanisms. The methodology compares predicted joint shear strength results with existing experimental results to obtain a reliable design approach. This comparison, along with verification of alternative analytical results, indicates the appropriateness of the presented model for predicting the shear strength of FRP-strengthened joints. Results contribute to the enhancement and efficiency of the practical design of these joints.

Bond durability between fiber-reinforced polymer (FRP) bars and concrete is a significant point of concern with respect to structural integrity, performance, and retrofit purposes. This experimental study addresses the bond durability of glass-FRP (GFRP) bars embedded in different concretes after exposure to harsh environmental conditions (i.e., seawater and an alkaline solution at 60° C). A total of 54 beam specimens of self-compacting, fiber-reinforced, and normal concretes were constructed, conditioned, and tested under flexural pullout according to RILEM provisions, which simulate the reinforcement behavior as a structural element in buildings. Sand-coated GFRP bars and steel bars were used to reinforce concrete beams. The obtained results demonstrated that the bond strength of beams with sand-coated GFRP bars decreased less after exposure to seawater in comparison with alkaline solution. However, the converse outcome was found for beams with steel bars. In addition to the reinforcing bars, the type of concrete was found to be effective in the bond durability of beams with both GFRP and steel bars under aggressive environments. Generally, the higher the density and strength, and the lower the permeability, the greater the bond strength and less its reduction.

Externally bonded carbon fiber–reinforced polymer (CFRP) composites have been instrumental in the flexural strengthening of concrete structures. However, intermediate crack debonding from the concrete substrate is a governing failure mode in most externally bonded CFRP applications, limiting the composite strength utilization and deformability of a strengthened member. The addition of transverse U-wrap anchorage for longitudinally oriented CFRP sheet tension reinforcement can improve performance in terms of both deformability and ultimate strength. Due to the scarcity of experimental data, design guidance for U-wrap anchorage to mitigate intermediate crack debonding is lacking. The results of flexural tests on large-scale reinforced concrete beams strengthened in flexure with externally bonded CFRP anchored with U-wraps are reported in this paper. Test results indicate that U-wraps can increase the strain utilization of longitudinal CFRP between 40% and 57%, while also mitigating the intermediate crack debonding failure mode. Varying the ratio of the area of U-wrap anchorage to area of flexural CFRP had little effect on the beams’ flexural capacity.

This paper reports an investigation on the damage tolerance of adhesively bonded pultruded glass fiber–reinforced polymer (GFRP) joints under fatigue loading. Double-strap joints with and without bondline defects were subjected to constant amplitude fatigue loading. The study investigated the effects of the defect location, size, and number on the fatigue performance of the joints (i.e., failure mode, fatigue life). Results showed that the failure mode was a combination of delamination and adhesive fiber–reinforced polymer (FRP) interface debonding at the defect vicinities. The fatigue life of the joints was significantly reduced (up to 90%) when the defect was at the overlap end. A defect size larger than 10% of the total bonded area could yield a substantial reduction in fatigue life. Small defects (less than 10% of the total bonded area) could yield a reduction in fatigue life of up to 73% when their number exceeded four. The joint exhibited better damage tolerance under static than fatigue loading conditions.

Finite-element (FE) modeling of sandwich panels with bidirectional flax fiber–reinforced polymer (FFRP) faces and polyisocyanurate foam cores in two-way bending under concentrated loads was performed. In addition, three large-scale (1,200 × 1,200 mm) sandwich panels with FFRP faces of various thicknesses (one, two, or three layers of flax fabric) and 75-mm-thick foam cores were tested under a concentrated load. The modeling was completed using commercially available software. The material nonlinearity of both the FFRPs and the foam cores was considered as well as the geometric nonlinearity due to localized deformation. Four failure modes were considered: FFRP compression crushing, FFRP tensile rupture, core shear, and compression-face wrinkling. Using the verified model, a parametric study investigated the effect of foam core density, face thickness, core thickness, and size of the loading area. It was found that panels with low-density cores were more susceptible to face-wrinkling failure, while panels with high-density cores were susceptible to both tensile rupture and core-punching shear failure. It was also shown that an increase in the diameter of the loading area decreased the effect of localized deformation for panels with high-density (96 kg/m³) cores.

The validity of the stability resistance factor in the moment magnification procedure for the analysis of slender columns reinforced with fiber-reinforced polymer (FRP) bars (FRP-RC columns) has not yet been considered in the literature. The development of such a factor, compatible with current building codes, is discussed in this paper. In the development process, first, the variability of the ultimate strength of slender FRP-RC columns was investigated, and the effect of variations in geometric and material properties on this variability was determined. The results of the variability study were later used in the first-order reliability analysis to estimate the appropriate stability resistance factor. The results of the analysis show that a stability resistance factor of 0.75 or 0.7, depending on the flexural stiffness expression, is representative of typical slender FRP-RC columns. Thus, we propose the use of this value, in combination with the recommended load factors.

Abstract

Self-compacting concrete (SCC) features excellent flow ability without the need of vibration for compaction during casting. This makes it particularly suitable for application in hybrid fiber-reinforced polymer (FRP)-concrete–steel double-skin tubular columns (DSTCs), a high-performance structural form evolved from concrete-filled FRP tubes (CFFTs). In a DSTC, the space between the inner steel tube and the outer FRP tube for filling concrete may be narrow and the application of vibration may be difficult. However, because of the large shrinkage of SCC compared to traditional concrete of normal flow ability, the integrity and composite action of DSTCs with SCC become a major concern. To clarify this issue, an understanding of the behavior of CFFTs filled with SCC is an essential prerequisite. While a large number of studies have been published on CFFTs with normal concrete (NC), only limited studies have been carried out on CFFTs with SCC. This paper presents a comprehensive investigation on the effect of SCC on the behavior of large-scale CFFTs. Axial compression tests were carried out on concrete-filled glass FRP (GFRP) tubes with diameters of 150, 200, 300, and 400 mm. The compressive behavior of the CFFT specimens filled with NC, a nonexpansive SCC, and an expansive SCC (ESCC) was compared and discussed. The results showed that the specimens with nonexpansive SCC behaved differently compared to those with NC as a result of larger shrinkage, especially for large specimens for which the confinement level was lower. This situation, however, improved in specimens where ESCC was used. Finally, the test results were further analyzed using a theoretical model recently proposed by the authors’ group.

Practical Applications

This paper investigates the compressive behavior of glass fiber–reinforced polymer (GFRP) tubes filled with self-compacting concrete (SCC). SCC is a type of concrete featuring excellent flow ability and larger shrinkage than normal concrete (NC). The detrimental effect of shrinkage can be counterbalanced by using expansive cement to form expansive SCC (ESCC). Compression tests were conducted on SCC-, NC-, and ESCC-filled GFRP tubes. Their compressive behavior was compared and analyzed. It was found that the NC- and ESCC-filled specimens behaved similarly, while the SCC-filled specimens showed a stronger dilation tendency under axial compression and less satisfactory performance than their NC- and ESCC-filled counterparts when the confinement level was relatively weak. Therefore, the use of an appropriate amount of expansive cement or a strong level of confinement is recommended when SCC is used as the concrete infill in practical confinement applications. The findings of this study are useful for applications of SCC in composite columns, especially in situations where only a narrow space is available for concrete casting, such as casting composite columns with a narrow ring section.

Fiber-reinforced polymer (FRP) composites are widely employed as externally bonded reinforcement (EBR) systems for strengthening reinforced concrete members. More recently, a new technique, referred to as externally bonded reinforcement on grooves (EBROG), has been proposed, which is based on using a number of grooves throughout the concrete substrate to enhance the bond strength between the FRP composite and concrete. This study investigates the influence of groove depth on the resulting debonding process that can be observed in prestressed carbon FRP strips. To do so, prestressing force release tests were conducted on a series of EBR and EBROG FRP strips bonded to concrete specimens. Test results demonstrated that the fracture process leading to debonding of the EBROG specimens developed in a significantly different manner with respect to the case of EBR specimens. Specifically, fractures ran through deeper layers of concrete as the grooves became deeper. Numerical analyses are also proposed to scrutinize the actual bond–slip law characterizing both EBR and EBROG specimens. It was shown that a trilinear bond–slip law is appropriate for simulating the interface behavior in EBROG specimens.