Journal of Composites for Construction

Glass fiber-reinforced polymer (GFRP) reinforcement has been considered as a replacement for the traditional steel reinforcement, mainly due to its corrosion resistance. In this paper, a total of 13 concrete columns and beams (length/diameter = 5.3) fully reinforced with GFRP longitudinal bars and spirals were experimentally studied. An additional two reference columns were also constructed with steel rebars and GFRP spirals to quantify the effect of the long bars. Factors such as the number of longitudinal bars, the pitch of the spirals, and load eccentricities were examined. It was found that the load capacities of the specimens with GFRP reinforcement were up to 12.3% lower than those with steel reinforcement; however, with sufficient transverse reinforcement, the GFRP-reinforced specimens were up to 15% more ductile. Reducing the pitch of the GFRP spirals and increasing the number of longitudinal reinforcing bars both resulted in an increase in the ductility and load capacity, demonstrating the contribution of transverse and longitudinal reinforcement. Strains well beyond the ultimate strain capacity of the concrete were measured in the longitudinal GFRP bars, illustrating the significant confinement provided by the spirals. The experimental results were favorably underpredicted by the recommended simplified method derived in this paper. In order to simplify the design process of circular members, a factor β_c was introduced to the current design rules in the international design standards and validated by the experimental results.

The effects of freeze–thaw cycles on the fiber-reinforced polymer (FRP)-to-concrete bond strength were investigated using the particle image velocimetry (PIV) technique. For this purpose, 18 specimens were prepared, including 12 specimens strengthened with carbon FRP (CFRP) strips as well as six control specimens subjected to 200 and 500 freeze–thaw cycles. The specimens were strengthened via externally bonded reinforcement (EBR) and externally bonded reinforcement on grooves (EBROG) methods. The results of PIV measurements revealed that, compared with the specimens strengthened via the EBR method, the EBROG-strengthened specimens exhibited considerably enhanced bond performance. When subjected to 200 and 500 freeze–thaw cycles, the EBR-strengthened specimens experienced a 3% and 9% decrease in their bond strength, respectively; the EBROG-strengthened specimens experienced no decrease in bond strength and increases in the range of 7%–19% when subjected to 200 and 500 cycles, respectively.

When used as an internal reinforcement, fiber-reinforced-polymer (FRP) composite bars are exposed to a highly alkaline (pH > 12.5) concrete environment. This study evaluated the durability of 24 types of FRP bars in a simulated alkaline concrete environment, specifically with respect to reinforcing-fiber type (carbon, basalt, and glass), fiber sizing, resin chemistry, and manufacturer. A total of 10 types of glass fibers, including two types of E-glass fibers and eight types of electrical corrosion resistance (ECR)-glass fibers, four types of basalt fibers, two types of carbon fibers, six types of resin systems based on vinyl ester, polyurethane, and epoxy resins, and five types of proprietary fiber sizings were used in manufacturing the bars. The study focused on assessing the tensile, transverse-shear, and interlaminar-shear properties of FRP bars subjected to 3 months of accelerated alkaline conditioning at 60°C, as per Canadian Standards Association (CSA) and American Society for Testing and Materials (ASTM) standards. The strength retention and failure of these bars were evaluated as a measurement of the durability and long-term performance of the FRP bars currently available on the market and for quality control by manufacturers. Statistical analysis using independent samples t-test and one-way analysis of variance revealed that the manufacturing parameters have a significant effect on the mechanical characteristics and alkaline resistance of FRP bars. In particular, the results show that the FRP bars manufactured with the same parameters and fiber types but by different fiber manufacturers with different fiber sizings and resin systems produced bars with totally different strength properties and durability performance in an alkaline environment. Vinyl ester resin and silane-sized fiber was the most compatible resin system and produced a more durable glass-FRP bar, while the epoxy resin yielded more durable basalt- and carbon-FRP bars. This paper also describes a procedure for and a criterion of the optimum manufacturing parameters to achieve specific mechanical properties and durability performance with FRP bars.

Axial load-bearing structural members often experience significant damage or failure when subjected to moving-vehicle or vessel collisions. Hollow steel tubular columns are highly vulnerable under transverse impact loading. Thus, strengthening/retrofitting of existing steel tubular columns may be required if these members are not designed to withstand expected transverse impact from transport accidents. This paper investigates the performance of full-scale circular-hollow-section (CHS) tubular columns strengthened with fiber-reinforced polymer (FRP) and subjected to vehicular impact. Initially, finite-element (FE) models of bare and FRP-strengthened CHS medium-scale specimens were developed to conduct transverse impact analysis for the model validation purpose. The impact simulation results were compared with the drop-mass impact test results and good agreements were found between the FE and experimental tests. The validated FE models were extended to full-scale bare and FRP-wrapped CHS columns. The full-column vehicle collisions were simulated using a realistic vehicle model by considering varying axial static forces and vehicle impact velocities. The results showed that strengthening with carbon-fiber-reinforced polymer (CFRP) improved the impact resistance capacity of a bare CHS column by preventing plastic hinge formation due to excessive local buckling when subjected to accidental vehicular impact. Three-layer CFRP strengthening proved to be an effective strengthening system compared with two-layer CFRP strengthening system. The effect of load eccentricity was assessed further, and it was found that CFRP strengthening contributed significantly to preventing the failure of CHS columns with varying eccentricities when subjected to credible vehicular impact events.

One promising polymer replacement to conventional petroleum-derived resins in fiber-reinforced polymers (FRPs) is furfuryl alcohol (FA) resin, which is a thermosetting resin derived from agricultural byproducts. In this study, 120 carbon FRP (CFRP) coupons were tested in tension to examine the fatigue behavior of FRPs with this resin, as compared to epoxy. Test parameters were the type of resin, the number of fiber layers, the manufacturing method, and the stress amplitude, ranging from 65% to 85% of ultimate strength. All specimens were tested in tension–tension with stress ratio R = 0, at a rate of 2.5 Hz. Fatigue life and stiffness degradation were monitored. As per ASTM E739 [ASTM. 2015. Standard practice for statistical analysis of linear or linearized stress-life (S–N) and strain-life (ɛ–N) fatigue data. West Conshohocken, PA: ASTM], a minimum of 75% replicates was used in this study. The normal life distribution, ASTM, and Whitney’s pooling scheme methods were used to determine reliability-based S–N curves. The phenomenological model by Whitworth was used to predict stiffness degradation. With an expected design fatigue life of 2,000,000 cycles, the allowable stress amplitude is predicted at 59% tensile strength using the ASTM method. Based on the Whitney model, this resulted in a stiffness retention of 80% for epoxy-based CFRP and 65% for FA-based CFRP at the end of life. Imaging was also used to assess the damage of the CFRP postcyclic loading. Epoxy-based CFRP showed transverse and longitudinal cracks in the matrix, whereas there was no visible damage on FA-based CFRP; however, environmental scanning electron microscopy showed that FA resin and carbon fiber had poor interfacial bonding.

Fiber-reinforced polymer (FRP) wrapping has been shown to be very effective in enhancing the static loading capacity of reinforced concrete columns. However, the impact performance of FRP-confined square concrete columns is still an unexplored field of study. This paper reports experimental results of relatively large-scale FRP-confined square and circular concrete columns subjected to axial impact, using a large-capacity drop-hammer machine. The main parameters include type of FRP, number of FRP layers, and the corner-rounding radius ratio. The results indicate that the failure modes of square columns are strongly influenced by the corner-rounding radius ratio. As expected, the rupture locations of FRP are all in the corner region, where the strain distribution usually shows stress concentration. It is revealed that the actual rupture strain of FRP under impact is significantly lower than that under static load. Columns wrapped in glass FRP (GFRP) and basalt FRP (BFRP) performed better under impact loading than did columns wrapped with carbon FRP (CFRP). Compared with static loading results, the axial stress–strain response under impact exhibits a more complex behavior. Based on the experimental results, an equation is proposed for predicting the FRP confinement effect on concrete for circular and square cross-section columns under impact.

Experiments have demonstrated the effectiveness of fiber-reinforced polymer (FRP) materials for the seismic strengthening of deficient reinforced concrete (RC) beam–column joints. However, only a few studies have focused on the seismic response of joint subassemblies that are designed to withstand moderate seismic actions where a strong column–weak beam mechanism is expected. In these circumstances, the high strain demand on the beam's plastic hinge may be critical for existing FRP-strengthening layouts. The present work analyzes the results of three experiments on full-scale, poorly detailed RC beam–column joints, with a strong column–weak beam hierarchy tested in the as-built and FRP-strengthened configurations. The proposed FRP-strengthening layouts are designed according to the recent trend of minimizing the level of disruption caused by their application. Accordingly, light FRP-strengthening solutions that are applied to the joint panel wholly from the exterior of a building or have a minimum impact on its downtime are tested and their performance is analyzed in terms of the global and local response.

External prestressing with carbon fiber-reinforced polymer (CFRP) strips is currently a well-developed and widely used technique to strengthen reinforced concrete structures subjected to bending. This paper presents the development and experimental investigation of a novel anchor and tensioning system for the flexural strengthening of RC elements with prestressed CFRP strips. The research on anchorages comprised a series of small-, medium-, and full-scale tensile tests, which resulted in the development of a new anchorage type with a tensile capacity of 200 kN, as well as the relevant tensioning device. This new system was subjected to comprehensive tests on RC beams in the laboratory, in which the efficiency, feasibility and ergonomics of the system were examined. The CFRP prestressed beams exhibited a more than 50% higher carrying capacity than that of the reference beam without strengthening. They also proved to have lower deflections as well as a lower number of cracks. As a result of the research, an effective strengthening system was developed and examined in the laboratory. Its efficiency and feasibility were also confirmed in the field tests on a strengthened existing bridge, and recently it has been successfully implemented in practice.

Designing reinforced concrete (RC) columns reinforced entirely with fiber-reinforced polymer (FRP) bars requires an explicit definition of the slenderness upper and lower limits for use in code provisions. To date, limited research has focused on experimentally assessing the behavior of slender FRP-reinforced concrete (FRP-RC) columns. Therefore, North American codes and guidelines lack design provisions. This study was conducted to enrich the research database with a total of 20 full-scale columns reinforced with steel or glass FRP (GFRP) bars. The columns were 305 mm in diameter and had slenderness ratios of 14, 19, 23, 26, and 33 were tested under concentric and eccentric loading. The steel-reinforced columns were tested to serve as a benchmark for their GFRP-reinforced concrete (GFRP-RC) counterparts. The interrelated effects between the slenderness ratio and the load eccentricity level were investigated with four different eccentricity-to-diameter ratios of 0%, 16%, 33%, and 66%. Test results proved the efficiency of GFRP bars as internal reinforcement for slender RC columns. The research program was then extended, developing a second-order model for slender FRP-RC columns. A good correlation was observed between the experimental results and the model developed analytically. In addition, based on the stability analysis, it was found that the available design equation for stability failure of steel-reinforced concrete (steel-RC) columns was appropriate and could also be applied to GFRP-RC. Finally, the experimental results and the analytical model indicated that a maximum slenderness limit of 18 was appropriate for short GFRP-RC columns bent in a single curve.

The hollow-core fiber-reinforced polymer-concrete-steel (HC-FCS) column is a relatively new structural system consisting of an outer fiber-reinforced polymer (FRP) tube, an inner steel tube, and a concrete shell encased between the two tubes. HC-FCS columns have displayed superior structural performance compared to conventional reinforced concrete columns. However, there is a lack of experimental data on the durability of HC-FCS columns subjected to long-term saltwater exposure and elevated temperatures. This study experimentally investigates the performance of HC-FCS stubs immersed in simulated seawater solution with different elevated temperatures for up to 450 days. Sustained axial loads were also applied to the stubs during the immersion period to simulate the service load for a bridge column. After the conditioning regime, compression tests were conducted on the HC-FCS stubs. Split-disk tensile tests, scanning electron microscopy, energy-dispersive X-ray, Fourier transform infrared spectroscopy, and differential-scanning calorimetry tests were performed on the associated FRP rings for both the control and conditioned samples. The seawater immersion of the HC-FCS stubs caused resin cracks and fiber/resin interface debonding on the glass fiber-reinforced polymer (GFRP) tubes due to the swelling stresses generated by the absorbed moisture. No chemical reaction took place on the GFRP tube with seawater immersion. The normalized strengths, axial strain, hoop strain, and strength enhancement ratios of the conditioned HC-FCS cylinders continuously degraded as the immersion time and ambient temperature were increased, with the degradation of approximately 41% for 450 days of conditioning at 60°C. Using these results and the Arrhenius model, it is estimated that HC-FCS columns will display degradation up to 52% in their axial capacity during a 100-year service life if subjected to seawater at 27°C.

One of the aims of applying sustainable development to bridge infrastructure was to provide bridge owners with strengthening solutions that could lead to increased service life for existing structures. In the case of steel bridges, the assessment of the remaining service life is most often linked to the determination of structural deterioration caused by corrosion and fatigue. Damage caused by fatigue is very difficult to assess before crack initiation and is more likely to occur in older structures, where the phenomenon was not taken into account in designs before 1970. In addition, old steel materials display more brittle behavior. To meet these challenges, a preventive methodology for fatigue strengthening of steel structures was developed. The method begins with scheduling a fatigue design analysis of the existing construction to determine the most fatigue damage exposed construction elements of the bridge. The remaining fatigue life of these elements can be increased with a strengthening solution based on the use of adhesively bonded ultra-high modulus (UHM) carbon fiber–reinforced polymer (CFRP) plates, which were applied to a steel surface before failure indicators such as cracks arise. This article presents the development process of this preventive method and a demonstrative application to an existing bridge (Jarama Bridge). Strain measurement was carried out to verify the theoretical expectations of the reinforcement. Different parameters were studied, including the influence of low traffic volumes during the reinforcement application. The results proved the efficiency of this system for the structure under study.