Journal of Composites for Construction

The current study aims to develop and standardize laboratory and on-site testing procedures to determine the tensile strength of bent glass fiber-reinforced polymer (GFRP) bars for quality control and quality assurance purposes. The proposed method involves embedding L-shaped bent GFRP bars in concrete blocks and subjecting the bars to tensile pullout forces. The test results were verified by comparing the strength of 25 bent GFRP bars produced by five different manufacturers to that of 25 other samples tested according to current standards. In addition, another 110 specimens were also tested to investigate the influence of all the parameters on the results yielded by the testing protocol, including bar size, concrete compressive strength, tail length, concrete block and cover dimensions, loading rate, confinement with steel reinforcement, and GFRP shape. The comparison between the L-shaped testing procedure and that following the standard specification requirements resulted in a 4%–20% difference in tensile strength, with a lower coefficient of variations obtained from the L-shaped for all the tested bars. The results of the parametric study revealed that regardless of the bar type, a 300 × 300 × 600-mm concrete block without reinforcement with an anchor length equivalent to 12 times the bar diameter and a loading rate to induce failure within 1–10 min is suitable for any shape of GFRP bar up to No. 6 (20 mm). A fast-setting concrete that can attain a compressive strength of 48 MPa can be used to promptly determine the tensile strength of the bent bars on-site or in testing laboratories for qualification purposes. The testing procedure developed in the current study has been adopted and included in the new edition of Canadian’s specification for fiber-reinforced polymers.

Columns in earthquake-resistant reinforced concrete (RC) structures need to be adequately confined to provide satisfactory levels of stability and deformability. In circular RC columns, confinement can be provided by spirals or hoops. This paper presents an investigation of the glass fiber-reinforced polymer (GFRP) confinement reinforcement requirements in columns of moment-resisting frames. Six full-scale circular RC columns were tested under simultaneous axial loading and unidirectional cyclic lateral drift reversals. The studied parameters were longitudinal reinforcement type, transverse reinforcement shape and pitch, and axial load level. Test results indicated that the maximum spiral pitch of one-fourth the gross diameter of the column as per the Canadian code for FRP-RC structures was reasonable and sufficiently conservative. In addition, GFRP circular hoops require larger lap splice length than that specified by the Canadian Highway Bridge Design Code to provide comparable confinement to GFRP spirals. The experimental results were estimated by a simplified method based on available confinement models, codes and guidelines for FRP-RC structures. It is recommended to consider the compressive strength of GFRP longitudinal bars with a compressive strain limit of 0.002 in circular GFRP-RC columns.

This paper introduces a new concrete floor concept comprising embedded glass fiber-reinforced polymer (GFRP) I-beams and GFRP stay-in-place (SIP) structural forms spanning between the lower flanges of the I-beams. The forms are flat plates with T-up ribs. The flexural behavior in the direction transverse to the I-beams, which is more critical because of the bonded connection between SIP forms and I-beam, is investigated using 2,575 × 610 × 225 mm slab segments. Both connection tests and member tests were conducted. Different SIP forms, concrete thicknesses, and surface treatments were explored. Both adhesive bonding and mechanical fasteners were explored for the connection. Also, behavior in the negative moment regions of the floor was simulated by testing the specimen inverted. The connection with adhesive and mechanical fasteners failed at a 48% higher bending than that with adhesive only. Increasing GFRP form size (reinforcement ratio) increased stiffness but not strength, neither for the connection nor for the member, due to debonding failure modes. A case study of a floor design was presented and showed that adhesively bonded connections met the strength requirement. A design-oriented analytical model was developed to predict connection strength based on bond failure. It accounts for the nonuniform shear and peeling stresses and includes corrections for the imbalance between the SIP form and the I-beam flange, as well as the additional peeling due to bending in the SIP form.

Current standards establish methods for seismic assessment and objectives for retrofit of existing building structures and provide guidance for fiber-reinforced polymer (FRP)-based seismic retrofit measures for existing reinforced concrete (RC) structures. However, there is no agreed-upon methodology for assessing—and therefore establishing—the efficacy of an FRP retrofit. Similarly, as FRP retrofits are becoming common, there arises a need to assess FRP-retrofitted concrete members and structures for their subsequent postretrofit performance. In this paper, a data-driven approach to determining modeling parameters for FRP-retrofitted RC columns consistent with current standards is demonstrated and parameters for flexure-dominated column behavior are proposed. A refined backbone curve is proposed for FRP-retrofitted columns in which an incremental rotation capacity accounting for the improved behavior of the retrofitted column is prescribed. Modeling parameters for flexure-dominated columns are proposed.

External bonding (EB) of fiber–reinforced polymer (FRP) laminates has emerged as a popular method to strengthen reinforced concrete (RC) structures. The premature failure of these structures is induced by debonding across the FRP–concrete interface. The mixed-mode debonding of the FRP–concrete interface will be analyzed by a cohesive zone model (CZM) derived from the modified Mohr–Coulomb strength criterion. The partial derivatives of the normal and tangential stresses that concern the interfacial separations will be presented in this study, which will facilitate the program coding to implement the proposed model. The coupled mixed-mode CZM provided a detailed description of the initial debonding and propagation of the FRP–concrete interface through a full range mixed-mode debonding process. Parametric studies will be conducted to provide a clear understanding of the mixed-mode loading-dependent debonding process of the FRP–concrete interface. The proposed model could be utilized to effectively and efficiently analyze the mixed-mode debonding of the FRP–concrete interface.

Twelve concrete columns reinforced longitudinally with fiber-reinforced polymer (FRP) bars were tested under both concentric and eccentric loadings. The investigated parameters were the type of the FRP bar, the longitudinal reinforcement ratio, and the load eccentricity-to-width ratio. The test results showed that the columns reinforced with basalt-FRP (BFRP) and glass-FRP (GFRP) experienced similar load-carrying capacity with a difference of less than 5%. Both types of columns attained lower ultimate capacity than their steel-reinforced counterparts. The contribution of the GFRP and BFRP bars to the ultimate capacity of the columns was similar, approximately 11% of the capacity, as compared to 31% for the steel bars. The effect of increasing the reinforcement ratio on the capacity was more pronounced in the eccentric FRP-reinforced concrete (FRP-RC) columns than the concentric ones. The analytical investigation showed that ignoring the strength contribution of the FRP bars, as recommended by most of the current codes and design guidelines, would result in conservative predictions. It also showed that current Canadian design code recommendation limiting the strains in FRP bars in compression to 2,000 µɛ yielded reasonable predictions of the column capacity.

This paper addresses the durability of reinforced concrete beams strengthened with carbon fiber-reinforced polymer (CFRP) laminates under natural and saline environments in the Arabian Gulf. Beam specimens were conditioned under sunlight and saline water for 180, 360, and 730 days and tested under four-point bending until failure. The load–deflection curves, strains, failure modes, ductility, and stiffness of the exposed beams were evaluated. The CFRP-strengthened specimens exhibited a 67% higher ultimate load capacity than control specimens after 28 days and up to 51% and 71% higher load capacity than control specimens after two years of direct sunlight and saline water exposure, respectively. No pronounced loss in strength and stiffness or damage to the epoxy was observed. Failure modes were transformed from cohesive to adhesive due to saline water exposure, whereas sunlight-exposed samples exhibited no failure-pattern change, and failures remained cohesive or interfacial. For design and analysis, environmental strength reduction factors are proposed and compared to current industry guidelines. Thus, CFRP-strengthened laminates can endure and perform effectively when subjected to severe environments of high salinity, temperature, and humidity.

In this study, the grooving method was employed to strengthen reinforced concrete (RC) columns with longitudinal fiber-reinforced polymer (FRP) sheets, and the performance of columns was investigated under both concentric and eccentric loadings. Furthermore, the effects of longitudinal FRP sheets and the grooving method on the ductility of strengthened concrete columns were studied. For this study, 12 slender square concrete columns with a slenderness ratio of 25 were subjected to eccentric loading with various eccentricity-to-cross section ratios (e/h) equal to 0, 0.24, 0.48, and 0.72 (i.e., eccentricities of 0, 30, 60, and 90 mm). Externally bonded reinforcement (EBR) and externally bonded reinforcement on grooves (EBROG) methods were utilized for FRP strengthening of the specimens. The results demonstrated that for the eccentricity ratios of 0, 0.24, 0.48, and 0.72, the load-carrying capacity of the columns strengthened with the EBROG method increased by 10.6%, 19.6%, 68.8%, and 99.3%, respectively, compared to those of the nonstrengthened columns. Particle image velocimetry (PIV) analyses demonstrated that under all the loading conditions investigated, the grooving method effectively improved the column performance, including load-bearing and flexural capacities. Such analysis also revealed that the application of longitudinal FRP sheets led to significant enhancements in the ductility of the columns tested.

Glass fiber–reinforced polymer (GFRP) bars have been used in concrete structures as an alternative to steel bars due to their noncorrosive behavior. However, due to the lack of full understanding of long-term performance, their use as internal reinforcement is still limited. To evaluate the durability of in-service GFRP bars under natural exposure, a collaborative project including four organizations investigated the conditions of GFRP bars and their surrounding concrete from bridges with 15–20 years of service. The aim of Part I of a two-paper series is to describe the bridge structures, methods of extraction, and the results of concrete testing, wheras Part II focuses on GFRP bar performance. The extracted bars were tested for physical, mechanical, and chemical properties, and the surrounding concrete was evaluated for chloride penetration, pH, and carbonation depth at the level of reinforcement. Results showed that carbonation and chloride may have reached the depth of the GFRP bars. This paper discusses the process of extraction of the bars, including the location and type of the selected bridge, and the concrete tests performed in terms of procedure, results, and observations.

A multilaboratory investigation into the durability of glass fiber–reinforced polymer (GFRP) bars extracted from eleven 15- to 20-year-old bridges in the US will be performed. Part 1 (Benzecry et al., forthcoming) of this two-paper series describes the bridges and presents data on the condition of their concrete, and Part 2 focuses on the condition of the bars. Constituent content, maximum water absorption, as-received moisture content, glass transition temperature (T_g), short bar shear (SBS) strength, and tensile strength will be evaluated. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) will be performed. The fiber mass content of all bars was close to or greater than that specified in the current ASTM E1309 (ASTM 2011a) GFRP bar standard. SEM and EDS showed only slight signs of degradation, which was predominantly near the outer radius of the bars. The loss of SBS strength was slight to moderate in bars with control data for comparison. Tensile strength, which could only be evaluated in 1 bridge, showed a reduction of only 4.2% after 17 years of service. It was concluded that GFRP bars could be considered a promising replacement for steel reinforcement in bridge decks subjected to real-time field exposure.

The efficiency of the use of near-surface mounted (NSM) carbon fiber-reinforced polymer (CFRP) strips confined with CFRP wraps to strengthen reinforced concrete (RC) columns will be experimentally and analytically investigated in this paper. A total of 15 specimens of RC columns strengthened with different numbers of NSM-CFRP strips (0, 4, and 8) and confined with different numbers of CFRP wraps (0, 2, and 4), will be prepared and tested under concentric and eccentric loading with different eccentricity ratios of 0, 0.25, 0.50, and 0.75, respectively. The axial load capacity, lateral deflection (Δ), axial deflection, and longitudinal and transverse strains will be measured. The effects of NSM-CFRP strips, the number of CFRP layers, and the eccentricity ratio on the capacity of the specimen will be investigated. The strengthened specimens showed a significant increase in load-carrying capacity and ductility over the control specimens. The increase in the load-carrying capacity of the confined specimens strengthened with strips in axial and uniaxial bending reached 49% and 95%, respectively, over the control specimen. It was concluded that strengthening RC columns with NSM-CFRP strips wrapped with CFRP composite sheets enhanced both the capacity and ductility consistently, for all applied eccentricity ratios. In addition, an analytical model will be developed to predict the strength of NSM-CFRP-strengthened RC columns and will be validated using the obtained experimental results.