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Concrete is used as a material in the construction of several types of structures. The structural behavior of concrete is constrained by its lower tensile strength, bending strength, and toughness. Fiber-reinforced concrete is gaining importance in various concrete applications. Research has been carried out to use multiple types of fibers in concrete in different combinations to improve its mechanical characteristics, such as toughness, strength, ductility, and durability. In traditional concrete, microcracks have developed before loading the structure because of volume changes and drying shrinkage. When the load is applied, the microcracks start opening and propagating. Therefore, failure of the concrete member occurs. Hence, the usage of fibers helps arrest the growth of the crack and improves concrete characterization. The goal of this research study is to examine mechanical properties of concrete when used in combination with steel, basalt, and glass fibers. Steel fiber is useful in arresting macrocracks, whereas basalt and glass fibers are effective in preventing microcracks. In this research, the specimens incorporated hybrid (steel, glass, and basalt) fibers in the concrete mix with various percentage proportions at a 0.5% volume fraction. Experiments were carried out to assess the bending strength, compression strength, and splitting tensile strength. Therefore, this research can show comparative analysis for different percentages of fibers to enhance the qualities of concrete and can show the optimum fiber percentage among the proportions selected for this study. [ABSTRACT FROM AUTHOR]

The use of glass fiber‒reinforced polymer (GFRP) bars in seawater–sea sand geopolymer mortars (SSGMs) for coastal engineering has gained significant traction because of the potential to enhance the utilization of noncorrosive GFRP reinforcements and natural resources. However, the durability of GFRP bars under the combined impact of prestressing and SSGM cover in seawater environments must be further investigated. In this study, the tensile strength (TS), interlaminar shear strength, and transverse shear strength degradation of GFRP bars were evaluated through hydrothermal seawater aging tests with immersion temperatures including room temperature, 40°C, and 60°C for 83, 180, 270, and 365 days. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses were performed to investigate the degradation mechanisms of the GFRP bars after conditioning. The test findings indicated that the effect of increasing the thickness of the SSGM cover on GFRP durability was insignificant. However, without the SSGM cover, GFRP bars demonstrated superior strength retention than SSGM-covered bars after 365 days of seawater immersion because of the absence of alkali ion attack. With the application of prestressing, a greater reduction in strength retention was observed due to increased microcrack formation and penetration of OH− ions and water molecules into glass fibers. In addition, the test results were compared with the bars embedded with seawater–sea sand cement-based mortars, while the SSGM-covered GFRP bars exhibited higher TS retention under identical hydrothermal aging conditions. The high addition of ground granulated blast furnace slag in SSGM contributes to a more compact microstructure, resulting in reduced water diffusion from the outer part of the SSGM. Additionally, the strong alkali-binding capacity of the gel led to a decrease in the pH of the pore solution. [ABSTRACT FROM AUTHOR]

The performance of energy geostructures is dependent on the surrounding soil properties in the presence of high temperatures or thermal cycles. Change in temperature may affect many engineering parameters of soils. Sand-bentonite mixtures or bentonite, which are used as a buffer should keep their performance at design level for a long time. Purpose: In order to improve engineering behavior of soils under high temperatures thermally durable materials may be used. Volume deformation and hydraulic conductivity behavior of 30% bentonite–70% sand mixtures in the presence of fiberglass additives were investigated. Methods: Consolidation tests were performed at room and high temperatures (80°C), hydraulic conductivity tests were started at room temperature, and a temperature cycle (25°C, 50°C, and 80°C) was applied. Results: Fiberglass increased the amount of compression insignificantly under room temperature, whereas the total compression amount increased remarkably under high temperature. On the other hand, the hydraulic conductivity increased under high temperature with fiberglass additive. Conclusions: Fiberglass-added sand-bentonite mixtures can be used around energy structures as an alternative buffer material with high-temperature resistance. [ABSTRACT FROM AUTHOR]

This paper aimed to study the compatibility between E-glass of chemical resistance (ECR-glass) fibers and the polymer matrix and the influence of different matrix types on the durability performance of ECR-glass fiber–reinforced polymer (GFRP) bars in a marine concrete environment. Two types of matrices, epoxy and vinyl ester, were employed to fabricate GFRP bars, which were then subjected to accelerated exposure by immersion in a simulated seawater sea-sand concrete (SWSSC) pore solution. The degradation performance and damage mechanism were thoroughly investigated. The results indicated that hydrolytic degradation of the cured epoxy and vinyl matrices and subsequent chemical etching to glass fibers are the primary damage mechanisms affecting GFRP bars in the SWSSC environment. Based on these mechanisms, two damage models were proposed: a chemical etching-based model and a hydroxyl ion diffusion-based model. These models enabled the prediction of the residual tensile strength of GFRP bars in the SWSSC pore solution environment at different temperatures. The accuracy of the proposed models was validated through comparisons with experimental data. [ABSTRACT FROM AUTHOR]

This paper reports on the compressive properties of a new steel wire– and carbon/glass hybrid fiber–reinforced polymer (S-CG HFRP) bar. The influence of the carbon and glass fiber volume proportion (Vc/Vg), steel wire replacement ratio (Vs), fiber volume ratio (Vf), fiber arrangement, and ratio of the unbraced length to the bar diameter (Lu/d) on the compressive behavior of the S-CG HFRP bars was experimentally investigated. The failure mechanisms were analyzed, revealing that the failure mode changed from fiber microbuckling to fiber macrobuckling with an increase in Lu/d. Adding steel wires resulted in a decrease in the compressive modulus of the S-CG HFRP bars. The compressive strength of the S-CG HFRP bars was not effectively improved by adding steel wires or carbon fibers and was governed by the Lu/d ratio. The results showed that the compressive modulus and strength of the S-CG HFRP bars were approximately 90% and 28% of their tensile modulus and strength, respectively. Finally, the relationship between the compressive and tensile properties of the S-CG HFRP bars was established. Simplified empirical equations were proposed to estimate the compressive strengths of S-CG HFRP bars with different Lu/d ratios. [ABSTRACT FROM AUTHOR]

This study evaluates the degradation of glass fiber reinforced polymer (GFRP) rebars in alkaline environment under accelerating aging in terms of tensile strength retention (TSR). In addition to environmental conditions such as the pH of the surrounding solution, temperature, and aging duration, the manufacturing parameters of GFRP rebars (i.e., diameter of rebar, db) and volume fraction (Vf) are vital in the degradation of GFRP rebars in alkaline environments as well as scarcely reported. To assess the effect of these variables on the degradation (i.e., TSR), shapely additive explanations (SHAP analysis) based on light gradient-boosting machine (Light GBM), and statistical analysis using response surface methodology (RSM) were used. The Light GBM and RSM models were developed using 715 experimental results of TSR obtained from the existing literature. The performance of both models was reliable in terms of correlation and error analysis. The interaction among the variables was further analyzed using detailed explanations of how each variable affected the prediction of TSR. The results revealed that the TSR generally increases at higher Vf and db of GFRP rebars; however, it decreases with increasing pH, temperature, and duration of exposure. Furthermore, maximum TSR was recorded for pH of 12.6 (Vf=0.62−0.70 and db=14–16 mm). Finally, severe degradation was observed for rebars having 0.55>Vf>0.70. The findings of this study suggest that the current practice of various structural codes using GFRP rebars having minimum mass fraction of 70% (≈0.48Vf) could be improved by using the range of Vf determined in this study to minimize the degradation in alkaline environments. The current research identifies the key production parameter effects of GFRP rebars on durability in harsh alkaline environments. The effect of high pH, surrounding temperature, and aging duration, among others, is well understood. However, a study on the effects of GFRP rebar size (diameter of rebar, db) and volume fraction (Vf) of fibers would help manufacturers to improve the quality of the GFRP rebars impregnated in vinyl ester resin. Also, the practitioners may use the recommended db and Vf in designing durable GFRP-reinforced structures. This study also identifies the research gaps, where a scarce amount of literature is available on GFRP rebars exceeding 16 mm. The formulated models can further be used for long-term extrapolation of service life of the GFRP rebars based on surrounding harsh alkaline environmental conditions. The basic assumptions considered in evaluating the durability of the GFRP rebars can be overcome. [ABSTRACT FROM AUTHOR]

The load-transfer mechanism in the fiber-reinforced polymer (FRP) bars is different from that of the conventional steel bars. The efficiency of stress transfer in FRP bars mainly depends on the mechanical properties of matrix resin, fibers, and fiber/matrix interface, which are easily degraded after long-term exposure to concrete environment. Herein, the interlaminar shear properties of a novel carbon/glass hybrid fiber-reinforced polymer (C/G-HFRP) bar were experimentally investigated by the accelerated aging tests at 60°C to study the effects of the ratio of carbon to glass fiber volume fractions, distribution configuration of carbon fiber, total fiber volume fraction, exposure environment, and exposure period. Water uptake tests, scanning electron microscopy, and Fourier transform infrared spectroscopy were employed to explore the degradation mechanisms of exposed samples. The results indicated that the interlaminar shear strength (ILSS) retention of exposed C/G-HFRP bars was higher than that of the single glass-FRP bar, which was decided by tooth force and friction. In addition, the degradation of C/G-HFRP bars was also related to water uptake rate, and then waterproof coating and fiber modification are recommended to improve the durability of C/G-HFRP bars. Finally, a model of ILSS retention was proposed for the C/G-HFRP bars after exposure to different concrete environments. [ABSTRACT FROM AUTHOR]

The structural performance of concrete structures requires swelling the bending and shear characteristics of reinforced concrete (RC) beams. The bending characteristics of RC beams consisting of waste granite aggregate (WGA), steel fibers (SF), polypropylene fibers (PF), and glass fibers (GF) are assessed in this research. Twenty-one 2,000 mm×200 mm×250 mm RC beams were cast and tested. WGA was sorted and utilized instead of natural coarse aggregates (NA), with three mass replacement fractions: 0%, 50%, and 100%. Besides, SF, PF, and GF were utilized separately at three fractions of 0%, 0.5%, and 1%. Beams were loaded under a four-point bending arrangement, and the ultimate bending resistance, deformability, stiffness and crack development were recorded and assessed. Also, an evaluation of experimental results and existing design standards in terms of maximum crack width has been carried out. Moreover, a cost-sensitivity examination has been made to analyze the effectiveness of using various fibers in terms of cost. Experiments revealed that the impact of PF on enhancing the load-bearing capability of beams with WGA was greater than that of strengthened with SF and GF. However, the impact of GF on the ultimate deformability of WGA RC beam samples was superior to that of PF and SF. PF has a greater influence on enhancing the flexural capacity of RC beams than SF; nevertheless, SF has a greater influence on deformation. The ductility and deformability of RC beams were substantially enhanced when GF was introduced in specimens made with WGA. [ABSTRACT FROM AUTHOR]

The incorporation of fiber into cementitious composites is considered a reassuring way to enhance its mechanical properties. However, high-temperature exposure can severely affect it. This investigation aims to study the high-temperature behavior of cementitious composite containing steel and glass fibers from microstructure to mechanical properties. To examine the compressive and tensile strength, the specimens were heated to the target temperature (200°C, 300°C, 400°C, 650°C, and 800°C) and tested in the hot state. The volume fraction for steel fiber was 0.25% and 0.5%, and for glass fiber, it was 0.25%. Moreover, to examine the microstructural transformation, scanning electron microscope, X-ray diffraction, and thermogravimetric analyses were conducted on the samples extracted from the heated specimens. Based on the results, the mortar containing steel fiber enjoyed better mechanical strength at high temperatures. The inclusion of steel fibers could improve the compressive and tensile strength of the normal mortar, on average, by 9% and 14% at 400°C. However, the excessive inclusion of those adversely affected the compressive strength, particularly at temperatures above 650°C. Moreover, all types of mortars experienced a fluctuation phase in their mechanical strength at the range of 28°C–400°C resulting from rehydration of portlandite and evaporation of free water. The main reduction branch commenced at temperatures above 400°C, where decomposition of portlandite and microcrack development were noticeable. [ABSTRACT FROM AUTHOR]

This article presents the results of research on sandwich materials manufactured by liquid resin infusion and designed to resist in low-velocity/low-energy impact applications. The sandwich plates are made of composites skins [glass fiber reinforced plastic (GFRP)] on a foam core. A manufacturing method was designed to produce samples in a one-shot process. Four manufacturing parameters were selected and combined: resin's temperature, preform's temperature, hardener type, and presence of nanoscaled additives. Their influences on the behavior of the samples during impact and the resulting damages were investigated. For each manufactured plate, nine samples were impacted with a 10 J drop-weight tower. Impacted samples were inspected with two nondestructive testing methods, visual inspection and infrared thermography. Samples were cut afterward to confirm conclusions and observe in-depth damages. Two impact behaviors and three damage types have been identified among all tested samples. The impact properties of the samples can be directly linked to the processing conditions. To ensure uniform mechanical properties, plates should be manufactured with isothermal conditions (same temperature in the preform and in the resin). If the manufacturing temperature is high enough, there is no significant influence on the impact behavior of the sandwich samples using slow or standard hardener. The higher the infusion temperature is, the more brittle the resulting composite. With nanoadditives in isothermal conditions, the resin's viscosity is much higher, leading to a longer infusion and nonuniform properties. [ABSTRACT FROM AUTHOR]

This study numerically investigated the effect of fiber-reinforced polymer (FRP) laminates on the shear transfer capacity of strengthened push-off concrete specimens. The numerical model compared the shear transfer values in uncracked specimens strengthened with internal steel reinforcements and external glass fiber reinforced polymer (GFRP) layers of different widths and thicknesses. The increase in shear transfer capacity in the strengthened specimens was assessed, and a parametric study was carried out on the FRP laminates at different types, widths, thicknesses, and fiber inclinations. An equation for calculating the FRP shear stress has been proposed and tested for validation. The results indicated that the gain in shear stress from the use of FRP laminates depends on the type, width, thickness, and fiber inclination of the laminate strips. [ABSTRACT FROM AUTHOR]

Steel reinforcing bars, helices, and fibers in concrete columns are susceptible to corrosion, particularly in aggressive environments. This study experimentally investigated the use of corrosion-free glass fiber-reinforced polymer (GFRP) bars and GFRP helices in hollow-core circular glass fiber concrete (GFC) columns. The influence of the addition of the glass fibers, loading conditions, and pitch of the helices was investigated. The experimental program consisted of 12 circular specimens with an outer diameter of 214 mm and an inner circular hole diameter of 56 mm. Nine specimens (850 mm high) were tested under concentric and eccentric axial loading and three specimens (1,500 mm long) were tested under four-point bending. The experimental results showed that, for a similar amount of reinforcement, the GFRP bar-reinforced hollow-core glass fiber concrete (GFRP-HC-GFC) specimens achieved 12%–18% lower maximum axial load than the GFRP bar-reinforced hollow-core nonfibrous concrete (GFRP-HC-NFC) specimens under concentric and eccentric axial loadings, as evident in the P–M interaction diagrams of GFRP-HC-NFC and GFRP-HC-GFC. However, GFRP-HC-GFC specimens achieved 5%–20% higher ductility than the GFRP-HC-NFC specimens under different loading conditions. The experimental results also showed that the GFRP-HC-GFC specimens experienced a lower number of cracks and smaller crack widths than the GFRP-HC-NFC specimens under eccentric axial loading and four-point bending. In addition, the GFRP-HC-GFC specimens with 30-mm pitch of the GFRP helices achieved 2%–34% higher maximum load and 7%–55% higher ductility than the GFRP-HC-GFC specimens with 60-mm pitch of the GFRP helices under different loading conditions. [ABSTRACT FROM AUTHOR]

This paper presents a series of single fiber pull-out tests on steel and glass fiber embedded in a cementitious matrix. First, the phase of fiber sliding in the concrete matrix was defined using a shear lag model; then, governing equations for the sliding mechanism were derived using the analytical model. FEM analysis was then used to calibrate the frictional coefficient. Further analysis related to the pressure exerted on the fiber by the surrounding concrete revealed that a smaller fiber diameter would improve bond strength. In terms of the relationship between pressure from the surrounding concrete and the diameter of the fiber, the results showed that a smaller fiber diameter would increase the matrix pressure; improved frictional bond strength and behavior would be expected compared to larger fiber diameters. The results also showed that decreasing fiber diameter by 75% would improve the frictional bond strength by as much as 300% for smooth and straight steel fiber, whereas reducing the fiber diameter by 66% would improve the frictional bond strength by 190% for single glass fibers. In addition, the results showed that a smaller diameter of the fiber improves interfacial properties between the fiber and concrete in fiber-reinforced concrete (FRC) composites. [ABSTRACT FROM AUTHOR]

The main objective of this study was to evaluate the use of glass fibers and cement as stabilizing agents for highly expansive soil. Fibers with two aspect ratios (12 and 30 mm in length) were added as percentages of the soil's dry weight (0.5%, 0.75%, 1%, and 1.5%), the cement was added in two percentages by dry weight soil (2% and 6%). Sixteen groups of treated soil specimens were prepared and subjected to laboratory tests—unconfined compressive strength (UCS) after curing (0, 7, 14, and 28 days), swelling percentage, and California bearing ratio (CBR). Interactions at the interface between the fiber surface and the soil matrix were analyzed by scanning electron microscopy (SEM). Also evaluated was effect of fibers on the design and performance of cement-stabilized subgrade layers according to the Mechanistic-Empirical Pavement Design Guide (MEPDG) to compare the performance of flexible pavement sections modeled using default values and laboratory-established soil properties for inputs. Results indicated increases in UCS and soaked CBR and decreases in swelling tendency. The 6% cement/1.5% short fiber mixture resulted in a significant improvement in expansive soil properties over other mixtures. [ABSTRACT FROM AUTHOR]

In this study, the fresh properties, fracture energy, compressive strength, and flexural strength of self-compacting concrete including glass or basalt fibers were examined, and the effect of fibers on these properties were studied comparatively. For this purpose, fibers having three different lengths (6, 12, and 24 mm) were used in two different contents (2 and 4 kg/m3). The workability of concrete mixtures decreased with fiber addition. The negative effect of basalt fibers on workability was greater than that of the glass fibers. The reduction in flow diameter was up to 40% and 44% as well as the reduction in L-box ratio was up to 41% and 48% in glass and basalt fiber mixtures, respectively. While the fiber addition generally reduced the compressive strength, it increased the flexural strength and fracture energy significantly. Increase in flexural strength was up to 58.6% in glass fiber and 43.5% in basalt fiber mixtures. The fracture energies of glass and basalt fiber mixtures were up to 55.1% and 30.4% higher than that of the control mixture, respectively. [ABSTRACT FROM AUTHOR]

An innovative precast segmental bridge column (PSBC) was proposed to achieve a better durability performance in an aggressive coastal environment, which was reinforced with both longitudinal stainless steel (SS) bars and glass fiber reinforced polymer (GFRP) bars. Four 3/20-scale PSBCs with various ratios of GFRP to SS bars were tested quasi-statically. Test results showed that compared to SS-reinforced PSBCs (SR-PSBCs), the SS-GFRP-reinforced PSBCs (SFR-PSBCs) exhibited higher displacement ductility, less stiffness degradation, lower postyield stiffness ratios, and smaller residual drift ratios, although they presented lower lateral loading capacity and energy dissipation. Increasing the ratio of longitudinal GFRP bar to SS bar in SFR-PSBCs resulted in higher displacement ductility performance and more gentle stiffness degradation behavior. Furthermore, the increase of axial load affects the seismic behavior of SFR-PSBCs in an unfavorable way, which could result in severer damage, significant reduction in the displacement ductility, faster stiffness degradation beyond the peak lateral strength point, and increase in the residual displacement. [ABSTRACT FROM AUTHOR]

Sulfate-rich dispersive soils are worldwide responsible for damaging earthworks, such as roadway roadbeds and embankments. One of the causes for such behavior is the high amount of exchangeable sodium ions adsorbed on their clay particles vastly increasing erosion susceptibility, being responsible for problems as piping, ravines, and water turbidity. In order to reduce the erodibility, it is usual to treat such soils with calcium-based stabilizers. However, in the presence of sulfates, when combined with calcium-based stabilizers in the soil, reactions take place between stabilizers and sulfates to form expansive minerals. Namely, these minerals are known as ettringite and thaumasite and are responsible for excessive volumetric swell. In this context, the present research aims to develop alternative soil stabilizers (industrial byproducts plus artificial pozzolans) and reinforcements (fiberglass) to solve problems associated with sulfate-rich dispersive soils. Thus, a binder composed of carbide lime and ground glass was used. In addition, fiberglass was applied to look for enhanced mechanical properties of the materials. To assess the efficiency of the proposed stabilization and reinforcement, unconfined compressive and splitting tensile strength, ultrasonic pulse velocity, wet and dry durability, and fatigue life tests were carried out. Soil–ground glass–carbide lime-fiberglass blends were molded at different porosities, carbide lime, ground glass, and fiberglass contents. Results show that unconfined compressive and split tensile strength and initial shear modulus are highly dependent on changes in porosity and lime content. Durability, expressed as the accumulated loss of mass, could be assessed through the adjusted porosity/lime index (η/Liv). Fiberglass inclusion resulted in higher tensile strength. The fatigue life was correlated to the η/Liv index through a negative exponent. The greater the carbide lime level, the smaller was the fatigue life for all treated specimens. An increase in porosity results in fewer contacts between particles, whereas an increase in carbide lime content enhanced the specimen's rigidity. [ABSTRACT FROM AUTHOR]

The harsh Australian environment makes the use of steel reinforcement in concrete structures problematic on account of corrosion. The probability of corrosion damage will significantly increase in the years to come and will become a major problem not only in coastal regions but also in inland parts of Australia due to increasing carbon dioxide concentration, temperature, and relative humidity as a consequence of climate change. In the last two decades, glass fiber-reinforced polymer (GFRP) composite bars have become an alternative to steel reinforcement for reinforcing concrete structures exposed to harsh environments. The reinforcing material is noncorrodible, nonmagnetic, lightweight, and has high tensile strength, thus making it a viable reinforcing material for concrete structures. This paper provides the state-of-the-practice in the research, development, and application of GFRP bars, with the aim of properly informing the engineering community about this alternative, noncorrodible reinforcing technology. The paper also presents a strategy toward the development of fiber-reinforced polymer bar material specifications with the aim to ensure quality use and application of the GFRP material in a wide range of applications in Australia in the years to come. Moreover, the best practices and data presented in this paper will be very useful in the development of unified international standards and specifications for GFRP bars. [ABSTRACT FROM AUTHOR]

In this paper, the role of masonry joints in the textile reinforced mortar (TRM)-to-substrate bond is investigated through an experimental program employing double-lap/double-prism (DL/DP) shear bond tests. The TRM system is composed of a dry glass fiber textile and a cementitious mortar applied as an overlay onto unreinforced wall prisms made from solid clay bricks and a cement/lime based masonry mortar. Specimens with different bond lengths (BLs) and various mortar joints-to-bonded area ratios are examined. For all specimens, the shear bond strength of the TRM/masonry interface is larger than the respective strength of the textile/matrix interface the shear failure of which was the governing failure mechanism. For the BLs considered, an increase in the mortar joints/BL surface ratio led to an increase in the transferable shear load of the joints indicating a substrate dependent behavior. A critical discussion on the characteristics of this dependence is included in this paper highlighting the effect of the substrate on the modification of the in situ properties of the composite's matrix. Finally, for BLs larger than the effective BL an existing indirect bond-slip model was applied, therefore, a cohesive material law could be determined for each substrate modified textile/matrix combination. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Nine beams reinforced with glass fiber-reinforced polymer (GFRP) bars and one reinforced with steel rebars fabricated using high-strength lightweight aggregate concrete (HSLC) were tested under four-point bending with different steel fiber contents, reinforcement ratios, and bar diameters to investigate their flexural strength and serviceability performance. The test results showed that specimens with steel fibers exhibited a lower deflection and a higher load-carrying capacity. The reinforcement ratio significantly affected serviceability performance, but bar diameter had a marginal effect. Generally, at service-load levels, the specimens exhibited acceptable midspan deflections but greater crack widths compared to the limits recommended by the codes. The experimental ultimate strengths, midspan deflections, and crack widths were used to assess the accuracy of prediction equations in standards in the US, China, and Canada. Rational deflection models for GFRP-reinforced normal weight concrete (NWC) beams were proposed based on the results from the available literature and were modified by introducing two correction factors of 0.85 and 1.35 for the GFRP-reinforced lightweight aggregate concrete (LC) and steel fiberreinforced lightweight aggregate concrete (SFLC) beams, respectively. [ABSTRACT FROM AUTHOR]

This paper presents an investigation correlating tensile properties of glass fiber--reinforced polymer (GFRP) bars with the results obtained from flexural testing. Composite bars, in contrast to conventional steel, when used in structures exposed to aggressive environments can significantly increase the durability and lifetime. However, the use of GFRP bars in concrete structures is still limited due to the variability of mechanical properties and bar quality among different manufacturers. Rational and fast testing methods for these reinforcing bars are needed. A flexure test is relatively easy and potentially could be used to determine the tensile strength of bars, which is a primary mechanical property that must be determined. This research investigates a possible correlation between the tensile strength and the modulus of rupture of GFRP bars. A Weibull weakest link model is employed. The effect of bimodularity of GFRP material in tension and compression also is investigated. [ABSTRACT FROM AUTHOR]

Bolted joints are critical in bracing elements subjected to seismic loads. When fabricated out of glass fiber reinforced polymers (GFRP), joint capacity is limited by the shear strength of the GFRP. We hypothesize that adding multiwalled carbon nanotubes (MWCNTs) to the epoxy resin prior to fabricating GFRP elements can improve the seismic resistance of GFRP bolted joints. Linear elastic structural analysis of a structure with GFRP bracing subjected to the 1940 El Centro earthquake was conducted. GFRP joints were fabricated using neat epoxy and epoxy nanocomposite incorporating 0.5% by weight MWCNTs. Bolted GFRP joints were tested under a seismic displacement time history identified using the finite-element (FE) model. Static tension test to failure was then used to determine the joint postseismic capacity. It is shown that the seismic resistance of GFRP bolted joints incorporating MWCNTs increased by 44% compared with neat GFRP joints. Furthermore, GFRP joints incorporating MWCNTs showed a postseismic static resistance that is 250% higher than neat GFRP joints and demonstrated a tension-stiffening behavior not observed in neat GFRP joints. [ABSTRACT FROM AUTHOR]

This paper presents an original study aimed at predicting the ultimate flexural and shear strengths of glass fiber--reinforced polymer (GFRP) RC squat walls subjected to quasi-static reversed cyclic lateral loading. Predicting the strength of GFRP-reinforced squat walls is critical for their safe design and acceptance of GFRP bar as reinforcement in such lateral-resisting structural elements. The test results of squat walls reinforced solely with GFRP bars have demonstrated their feasibility in resisting lateral loads and pointed to the necessity of adequate prediction of ultimate strength and failure modes. The predictions based on fiber-reinforced polymer (FRP) design codes and guidelines were investigated and compared with the test results of five large-scale GFRP-RC squat walls with different failure modes. The results demonstrated that in the one code, the concrete contribution to the shear resistance should be considered, and in other design guidelines, the 45° shear crack--angle assumption should be modified for squat walls with different properties and should consider the increase in concrete shear contribution after initiation of the first shear crack. The confinement at boundary elements has been shown to improve significantly the ultimate flexural strength that should be integrated in the design. [ABSTRACT FROM AUTHOR]

Glass fiber-reinforced polymer (GFRP) composites offer several advantages over loose-plate steel connections when used in vertical joints between concrete wall panels as a connector. Advantages include resistance to corrosion, higher tensile strength, and the ability to conform to uneven surfaces. The performance of continuous and intermittent GFRP composite connections between precast concrete wall panels under simulated seismic loads is investigated using six specimens. Each specimen was comprised of two precast concrete wall panels connected with a GFRP composite system. The laminate in the system consisted of bidirectional GFRP sheets applied in a wet layup configuration over a layer of epoxy--putty adhesive. The connection was applied on one side of the wall panels to meet architectural and construction demands. Cyclic shear was introduced to the GFRP composite connection through in-plane horizontal quasi-static cyclic loads, while horizontal and vertical constraints at the bottom and top corners of each specimen were engaged. The variables in the research are the presence of epoxy--putty adhesive in the seam between the wall panels, the percent of seam height covered with bidirectional GFRP composite, and the use of GFRP spike anchors. The presence of epoxy--putty adhesive in the seam significantly increased the horizontal load capacity of the GFRP composite connection. The use of GFRP spike anchors increased the horizontal load, horizontal displacement, shear transfer, and energy dissipation capacity of the GFRP composite connection. The GFRP composite connections performed very well and could be used in the seismic retrofit of existing connections between precast concrete wall panels. [ABSTRACT FROM AUTHOR]

Ten full-scale concrete deep beams reinforced with glass fiber-reinforced polymer (GFRP) with a cross section of 1,200 × 300 mm were tested to failure under two-point loading. The test variables were the configuration of web reinforcement (horizontal and/or vertical) and shear span-to-depth ratio (a/d = 1.47, 1.13, and 0.83), All specimens exhibited sufficient deformation required to develop arch action, which was confirmed by crack propagation and an almost linear strain profile in the main longitudinal reinforcement, inaddition to the typical failure mode of crushing in the concrete diagonal strut. The results show that the vertical web reinforcement had no clear impact on ultimate capacity, while the configuration with horizontal-only web einforcement unexpectedly resulted in a lower ultimate capacity compared to the specimens without web reinforcement. The web reinforcement's main contribution was significant crack-width control. [ABSTRACT FROM AUTHOR]

In this paper, test results of six large-scale glass fiber-reinforced polymer (GFRP) RC continuous T-beams are presented. The test specimens include one steel RC beam to serve as reference, one GFRP RC beam designed to meet the serviceability criteria at the service load level calculated for the reference beam, and four GFRP RC beams designed to achieve the same theoretical ultimate load of the reference beam. The test variables included the assumed percentage of moment redistribution, the spacing of lateral reinforcement in flange, and the arrangement of shear reinforcement. The test results showed that moment redistribution from the hogging to the sagging moment region occurred in GFRP RC beams with T-sections and that a small spacing of stirrups enhanced the moment redistribution percentage. In addition, decreasing the spacing of lateral reinforcement in the flange improved the moment redistribution through enhancing the stiffness of the sagging moment region. [ABSTRACT FROM AUTHOR]

This paper presents the results of a collaborative research project between Quebec's Ministry of Transportation and Ontario's Ministry of Transportation, which aimed at characterizing a new type of headed glass fiber-reinforced polymer (GFRP) reinforcing bar and evaluating its suitability as internal reinforcement for concrete structures. To achieve these objectives, the project was implemented in three stages: (1) evaluation of the physical and mechanical properties; (2) determination of the pullout behavior in concrete; and (3) characterization of the long-term durability of the headed GFRP bars. A total of 57 specimens embedded in a 200-mm concrete cube were tested with the direct pullout test to investigate the effect of confinement, bar size, concrete compressive strength, and exposure conditions on the pullout behavior of the headed GFRP bars. Simultaneously, microstructural analyses and measurements of the physicochemical and mechanical properties were carried out on conditioned and unconditioned headed GFRP bars. The results show that the materials, geometry, and interface configuration of the head provided very good mechanical interlocking to the GFRP bars. Up to 63 and 53% of the guaranteed tensile strength of the straight GFRP bars were achieved for 15.9- and 19-mm diameter bars with headed ends, respectively. Scanning electron microscopy and differential scanning calorimetry showed no material changes in the head and bars after exposure to alkaline solution and freeze-thaw cycling. Exposure to the alkaline solution under sustained loading had the most detrimental effect, with the bar retaining 79.4% of its pullout strength. The results indicate that the tested headed GFRP bar has suitable mechanical and durability properties for use as reinforcement in concrete bridge components. [ABSTRACT FROM AUTHOR]

This paper presents a simplified method of analysis and design for the repair of deteriorated timber beam ends using glass fiber-reinforced product (GFRP) bonded rigid plates. It assesses the load-bearing capacity of the plate-timber connection and assumes two failure modes: shear stresses at the bonding interface and in the timber piece. An experimental method was developed to verify the theoretical model for bending moment and shear force transfer. Ten short span beam specimens of Pinus radiata D. Don were spliced with bonded-in plates in one end, and they were tested by bending with different anchorage lengths to establish a relationship with load-carrying capacity. Furthermore, the effect of temperature (-20 to 50°C) and moisture content (9-30%) changes were analyzed in two groups of six short beam specimens and in bonding shear test specimens using two different epoxy formulations. The theoretical model predicts conservative values of load-carrying capacity. Temperature and moisture changes cause a reduction of mechanical properties, but to different degrees depending on the epoxy formulation. [ABSTRACT FROM AUTHOR]

The behavior of slender high-strength concrete columns reinforced with glass fiber-reinforced polymer (GFRP) bars and spirals subjected to concentric and eccentric axial loads was evaluated. Large-scale tests were conducted for nine circular concrete columns (three short and six slender) reinforced with internal GFRP-spirals and either steel, GFRP, or a combination of steel and GFRP longitudinal bars. The short and slender columns had slenderness ratios equal to 10 and 49, respectively. Axial load tests were conducted with loads placed concentrically (short columns) and at two eccentricities (slender columns) to observe the general behavior associated with different geometric and loading conditions. The behavior of slender columns with small eccentricity (8.3% of the column size) was governed by material failure, while that of slender columns with large eccentricity (33% of column size) was governed by a buckling failure. The research shows that GFRP spirals and GFRP longitudinal bars are a viable method of reinforcement for slender concrete columns subjected to eccentric axial loads. [ABSTRACT FROM AUTHOR]

Damage of reinforced-concrete (RC) structures commonly occurs during major earthquakes, and becomes worse because of aftershocks. For these reasons, repair technology for seismic damage is needed to prevent possible collapse of damaged RC structures before aftershocks. In this paper, a seismic retrofitting device is proposed to improve the seismic performance of damaged RC columns using glass fiber-reinforced polymer (GFRP), which can be easy to install and quick to repair. The proposed GFRP-strip device consists of a GFRP-composite strip and aluminum clip connectors, used to increase the shear strength of the damaged column. Three RC specimens were constructed with reference to existing RC structures. Two of the specimens were damaged before installing the GFRP-strip devices. After the pretest damage was done, the GFRP-strip devices were installed along the plastic-hinge regions on both ends of the test columns. A comparison of the experimental results indicates that the seismic performance of the damaged RC columns with the GFRP-strip device was improved, and that the shear-failure mode of the RC columns was changed to ductile-flexural-failure mode. According to these results, the maximum strength, accumulated-dissipated energy, and displacement ductility of the retrofitted specimens was increased. Therefore, the proposed GFRP-strip device can be used to improve the seismic performance of damaged RC columns. [ABSTRACT FROM AUTHOR]

This paper reports on the shear behavior of concrete beams reinforced with basalt fiber-reinforced polymer (BFRP) bars. In this study, 10 reinforced concrete beams with no transverse reinforcement, including 2 beams reinforced with longitudinal steel bars, were constructed and tested until failure. The test variables were the longitudinal reinforcement ratio and the span-to-depth ratio of the beams. The test results were compared with predictions of different available codes and design guidelines. Shear design equations of the CAN/CSA-806-12 code and the JSCE-97 guidelines provided accurate predictions. However, the predictions of CAN/CSA-806-12 were not conservative in some cases, whereas those of the ACI-440.1R-15 and the CAN/CSA-S6-10 were conservative. The test results were combined with the experimental results of a large database, including 75 beams and one-way slabs reinforced with carbon, glass, aramid, and BFRP bars. The behavior of beams reinforced with BFRP bars was quite similar to that of beams reinforced with glass and aramid fiber-reinforced polymer (FRP) bars. The test results demonstrate the potential of using BFRP bars as alternative reinforcement in concrete members. [ABSTRACT FROM AUTHOR]

The 26.87-m, single-span Beaver Creek Bridge on U.S. Highway 6 in Utah was built in 2009. Elements of the bridge included AASHTO Type IV prestressed concrete girders and posttensioned, full-depth, precast concrete deck panels reinforced with glass fiber reinforced polymer (GFRP) bars. The bridge was given three static and five dynamic truck load-controlled tests before it was opened to traffic. Vertical acceleration data was also collected from random truck traffic. Dynamic truck load data was used to verify a finite element model and obtain dynamic load allowance (DLA) values. DLA was determined to be a function of the number of axles, axle group weight, and axle spacing. The maximum DLA for the bridge with a GFRP-reinforced concrete deck was found to be less than the value specified in the AASHTP LRFD Bridge Design Specifications. [ABSTRACT FROM AUTHOR]

The use of bolted sleeve joints has been proposed for assembling pultruded glass fiber-reinforced polymer (GFRP) tubular profiles into space lattice shell structures. Such joint configurations may introduce a semi-rigid end condition and further affect the capacity of the connecting members in compression. Three batches of specimens assembled with pultruded GFRP profiles of different lengths and bolted sleeve joints at both ends were prepared and tested under static axial compression. A detailed three-dimensional finite element model considering bolt geometry, contact behavior, bolt pretension, initial geometric imperfection, and failure criterion for fiber-reinforced polymer (FRP) composites was developed and validated with experimental results showing good comparisons. It was found that the bolted sleeve joints exhibited semi-rigid behavior and that the failure modes and the effective length factor were dependent on member slenderness. The relationship between effective length factor and member slenderness was derived based on finite element analysis and then used in conjunction with existing FRP column design equations to predict the member capacity for structural members with bolted sleeve joint end conditions. [ABSTRACT FROM AUTHOR]

This paper presents an assessment of the seismic performance of concrete columns internally reinforced with glass-fiberreinforced polymers (GFRP) bars. Eight full-scale column prototypes with 1,650-mm shear span and 350-mm square cross-section were constructed and tested under combined lateral cyclic quasi-static and constant axial loading. The test specimens represent the lower portion of first-story columns between the footing and the contra-flexure point. The test parameters included longitudinal reinforcement type and ratio, level of axial load, and stirrup spacing. Test results showed that the drift capacity of GFRP-reinforced concrete (RC) rectangular columns at failure ranged between 8.5 and 12.5%, which exceeds the limitations of North American building codes. This indicates that the deformability of GFRP-RC column prototypes successfully replaced the ductility in steel–RC columns in dissipating the seismic energy in the presence of constant axial load. Furthermore, there was insignificant strength degradation before failure due to the well-confined concrete core. [ABSTRACT FROM AUTHOR]

The flexural failure mode of concrete beams reinforced with glass fiber-reinforced polymer (GFRP) bars changes from GFRP rupture to concrete crushing as the reinforcement ratio increases. Due to the uncertainties of material strengths, assumptions made in analysis, and variations in locations of reinforcements and dimensions of sections, there is a transition region where both flexural failure modes are possible. An iterative procedure is required when GFRP rupture governs the design. To avoid this iteration, the current American standard adopts a simplified but conservative procedure. In this study, the upper bound of the reinforcement ratio for beams in the transition region is revised. Moreover, a simplified yet rational design equation for calculating the flexural capacity of under-reinforced beams is proposed based on rigorous sectional analyses. Also, alternative design equations based on regression analyses are developed to predict the flexural capacity of beams in the transition region and over-reinforced beams, respectively. Moreover, the performance of the proposed equations is compared to that of design equations of recent standards by comparing their predictions with experimental results of 173 GFRP reinforced concrete beams collected from the available literature. [ABSTRACT FROM AUTHOR]

This paper studies the flexural performance of sandwich panels composed of a soft polyurethane foam core and glass-fiber-reinforced polymer (GFRP) skins. A robust numerical model is developed to predict the full load-deflection and strain responses of the panel. It is based on equilibrium and strain compatibility and accounts for the excessive shear deformation and material nonlinearity of the core. It also accounts for geometric nonlinearity in the form of localized deflection of the loaded skin using the principals of beam-on-elastic foundation and the change in core thickness due to its softness. The model incorporates various failure criteria, namely core shear failure, core flexural tension or compression failure, compression skin crushing or wrinkling, or tensile rupture of skin. The model has the advantage of being able to isolate quantitatively the individual contributions of flexure, shear, and localized skin deformations, to overall deflection. A parametric study is performed to examine the effects of core density and skin thickness on panel behavior. It is shown that as the core density increases from 32 to 192 kg/m³, the contribution of shear to overall deflection reduces from about 90 to 10%. It also appears that the optimal core density of the sandwich panels is within 96 to 128 kg/m³, which represents the lowest density necessary to achieve the highest ultimate strength and stiffness. [ABSTRACT FROM AUTHOR]

This paper presents finite-element analyses and analytical models of innovative, small-scale, prototype deck panels examined under monotonic bending. The deck panels consisted of two glass fiber-reinforced polymer (GFRP) facesheets separated by webs formed from E-glass-woven fabric placed around trapezoidal-shaped, low-density, polyurethane foam segments. The proposed panel exhibited a higher structural performance in terms of flexural stiffness, strength, and shear stiffness than those of conventional sandwich panels. Analytical models were used to predict critical facesheet wrinkling in the sandwich panel. Furthermore, a three-dimensional model using simulation software was developed for analysis of the proposed panel system under monotonic four-point loading. The finite-element results in terms of strength, stiffness, and deflection were found to be in good agreement with those from the experimental results. A parametric study was also conducted to further evaluate the effects of the stiffness of the top facesheet fiber layers, the mass density of the polyurethane foam, the existence of web layers, and the introduction of an overlay above the top facesheet. A flexural beam theory approach was used to predict the flexural strength of the sandwich panel. [ABSTRACT FROM AUTHOR]

The demand for sustainable concrete structures with longer service life and lower maintenance cost has been driving the use of glass fiber-reinforced polymer (GFRP) reinforcement in new concrete structures. The behavior of GFRP bars under seismic loading in reinforced concrete (RC) frame structures has not been widely investigated. Furthermore, the ability of FRP-RC frame structures to dissipate energy in seismic events is still questionable due to the elastic-linear behavior of the FRP reinforcement. Very few studies have been conducted on the seismic behavior of GFRP-RC exterior beam-column joints, and none studied the shear capacity of joints. Therefore, this study attempts to partially fill this gap by investigating the shear capacity of beam-column joints reinforced with GFRP bars and stirrups. Six fullscale exterior beam-column joint prototypes (T-shaped) were constructed and tested under simulated seismic load conditions. Test parameters in this study included the concrete strength and the shear stress level in the joint. Diagonal shear failure in the joint exhibited in some specimens showed the significance of evaluating the shear capacity in the joint. [ABSTRACT FROM AUTHOR]

Despite the fact that fiber reinforced polymer (FRP) composites are a reliable structural material with reasonable durability performance, the environment to which the strengthened structure is exposed can make the strengthening system vulnerable. In this study, the effectiveness of externally bonded reinforcement (EBR) systems when external compressive stresses are applied to glass fiber reinforced polymers (GFRP)-to-concrete interfaces in several aggressive environments is analyzed. The compressive stress imposed on the GFRP-toconcrete interface intends to simulate, for instance, the effect produced by a mechanical anchorage system applied to the EBR system. The design and the region to set those mechanical anchorage systems are not yet well understood and are mostly applied without really knowing how they will behave. This work shows an exhaustive experimental program based on several double shear tests subjected to salt fog cycles, dry/wet cycles and two distinct temperature cycles: from -10°C to +30°C and +7.5°C to +47.5°C. The Mohr-Coulomb failure criterion was found to provide a good representation of the performance of the GFRP-to-concrete interface, and changes of cohesion and the internal friction angle of those interfaces during the hours of exposure to the aggressive environments are reported [ABSTRACT FROM AUTHOR]

After 17 and 15 years of use, respectively, a detailed inspection of a pedestrian bridge and a 5-story building structure composed of partly adhesively bonded pultruded glass fiber-reinforced polymer (GFRP) profiles was conducted accompanied by full-scale serviceability and destructive coupon testing on exchangeable profiles. The bridge is exposed to a harsh Alpine climate and the building to a mild plateau climate. The system and material stiffness of the bridge remained unchanged during the 17 years. The material strength of the bridge, however, was significantly affected by combined freeze-thaw cycles and ultraviolet (UV) irradiation. The latter accelerated the strength degradation by uncovering the fibers (fiber blooming) and thus inducing humidity ingress into the material by wicking effects. A large majority of the small-area adhesive bonds in the bridge were intact, although a few small cracks were observed in some joints at the surface. The large-area bonds of the building did not show any damage. Based on results of the inspection of the bridge, the application of an appropriate coating on pultruded GFRP structures exposed to harsh environments is recommended. [ABSTRACT FROM AUTHOR]

Glass-fiber-reinforced polymers (GFRPs) are commonly used in various applications in civil-engineering projects. However, they are not common in the construction of civil-marine structures. The GFRP caisson technology was developed for the construction of two mooring dolphins in Puerto el Rosario (Fuerteventura, Spain). Ultraviolet-protected glass-fiber and epoxy resin coats were used to build a 12-m diameter, 13.3-m high cylindrical structure. A finite-element model was used to verify the sandwich composite configuration using the Tsai-Hill criteria--the shear strength of the skins and honeycomb core and the buckling and local failure modes with respect to the composite configuration. This is the first time that the two caissons were designed and built of polymeric materials and installed in a seaport. Accordingly, the construction technique marks a milestone in civil engineering because of its highly innovative nature in addition to significantly reducing the time associated with and the complexity of construction operations. [ABSTRACT FROM AUTHOR]

Glass fiber-reinforced plastic (GFRP) composite pipes are used in many diverse applications, including oil, gas, and power plants. These pipes are subjected to various harsh service conditions during their service life. The evaluation of mechanical properties and chemical resistance of these pipes is essential to assess their long-term performance in specific applications. The results of a study to evaluate the chemical resistance and mechanical properties of GFRP pipes for application in oil and gas plants are presented in this paper. Pipe specimens were preconditioned by filling them with 7.5% HCl, 8% H2SO4, and a mixture of 2% NaOH and 2% KMnO4 solutions maintained at 63°C. The preconditioned and fresh pipe specimens were exposed to clean and oily water [a mixture of 10% toluene, 10% kerosene, and 80% brine water (30 g=L NaCl)] maintained at 93°C and 1.5 × 106 Pa (15 bar) pressure for 1,000 h. The fresh, preconditioned, and exposed pipe specimens were tested to evaluate their axial and hoop tensile strength, water absorption, and loss on ignition. The experimental results did not exhibit major change in the properties of evaluated pipes owing to exposure to clean and oily water at high temperature and pressure. There was minimal or no loss in the axial and hoop strength of the preconditioned or exposed pipes. The absorption and loss of ignition did not increase significantly both due to pre-conditioning and evaluated exposure conditions. The results indicate that GFRP pipes are suitable for application in the oil and gas industry. [ABSTRACT FROM AUTHOR]

Six full-scale specimens were constructed and tested under reversal cyclic loading to study the seismic behavior of exterior glassfiber- reinforced-polymer (GFRP) reinforced concrete (RC) beam-column joints with lateral beams. Five specimens were completely reinforced with GFRP bars and stirrups and one was reinforced with conventional steel as a control specimen. The main test variables were reinforcing materials (GFRP and steel), presence of lateral beams, different joint shear stresses, and end anchorage of beam longitudinal bars (bent and headed-end bars). The specimens were subjected to increasing seismic drifts up to failure. Test results showed that GFRP-RC exterior beam-column joints confined with lateral beams can resist joint shear stress equal to 1.1 times the square root of the concrete compressive strength up to 6% drift ratio. In some cases, the specimens showed nonlinear behavior and nonbrittle failure, contrary to what it is expected from FRP-RC structures. Moreover, the anchorage method can change the mode of failure of GFRP-RC exterior beam-column joints. [ABSTRACT FROM AUTHOR]

The out-of-plane bending of sandwich panels has been widely investigated, but studies on their behavior under in-plane loading are quite scarce. In this study, 18 sandwich beam specimens were tested under three- and four-point in-plane-bending. The specimens are composed of low-density polyurethane core and glass fiber-reinforced polymer (GFRP) skins on both sides. The shear span-to-depth (a/h) ratio was varied from 1.33 to 4.67. Two different skin thicknesses were also used, providing beam depth-to-skin thickness (h/t) ratios of 47 and 94. It was found that the ultimate moment reduced by approximately one third as the a/h ratio increased from 1.33 to 4.67 in sandwich beams with an h/t ratio of 94 and decreased by about one quarter in beams with an h/t ratio of 47. Doubling the skin thickness [i.e., from h/t of 94-47] increased the moment capacity significantly. The percentage increase ranged from 55 to 95% as a/h increased from 1.33 to 4.67. Failure of sandwich beams occurred by skin wrinkling in compression, mostly symmetrically, where skins move in opposite directions. A simplified analytical model accounting for shear and flexural rigidities of the sandwich beam and a skin wrinkling failure criterion in compression was developed and validated against experimental results. [ABSTRACT FROM AUTHOR]

In this study, glass fiber silica aerogel composites were fabricated and used to protect steel frames against fire. Glass-fiber-coated silica aerogel was synthesized by immersing glass fibers into silica sol. Following gel formation, surface modifications were carried out. Samples were dried carefully at relatively high temperatures and ambient pressure. The samples were then prepared at two different solution pH values and four different aging times. Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) techniques have been employed to find the specific surface areas and pore diameters of the silica aerogel, formed as a coating on the glass fibers. Fourier transform infrared spectroscopy (FTIR) was used to investigate the chemical reactions. The coverage of fibers by the aerogel was also verified by scanning electron microscopy (SEM). To examine the composites' fire resistance, a laboratory turbotorch and infrared thermometer have been used. Fire was applied directly to the composite surface while the temperature was read on the other side. The relationship between the fire resistivity of the composites and physical characteristics of the aerogel such, as porosity and specific surface area, is discussed. [ABSTRACT FROM AUTHOR]

The use of basalt fiber-reinforced polymer (BFRP) bars as a reinforcing material has gained increasing interest worldwide. However, few studies have reported on these bars' performance in concrete when exposed to harsh environments. This paper investigates the effect of five different accelerated environments, namely (1) tap water, (2) seawater, (3) elevated temperature, (4) elevated temperature followed by tap water, and (5) elevated temperature followed by seawater, on the bond stress-slip response, adhesion to concrete, and bond strength [of two types of BFRP bars and one type of glass fiber-reinforced polymer (GFRP) bar]. The bond-slip responses of all specimens were governed by the surface treatment of each bar and its manufacturing quality, regardless of the fiber type. Sand-coated BFRP bars showed higher bond characteristics than helically grooved bars after conditioning. Moister environments caused enhanced adhesion at the early loading stages for all specimens. Nevertheless, such environments had a detrimental effect on the bond strength at later stages depending on the bar material's moisture absorption. Finally, exposure to elevated temperatures caused insignificant variation in the bond strength of all tested specimens. [ABSTRACT FROM AUTHOR]

The ACI and CSA design codes offer no unified method for evaluating the deformability of fiber-reinforced polymer (FRP) reinforced-concrete (RC) structures, although numerous experimental results for such elements are available. This study discusses the methods for quantifying the deformability in FRP-RC structures. The methods were assessed based on the experimental results of four full-scale RC shear walls: three reinforced with FRP bars and one with steel bars. The objective was to contribute to the development of a method for verifying the deformability of FRP-RC structures. The curvature ductility index (μΦ) and deformability index (J) were found to be the most appropriate methods when calculated at a concrete strain equal to 0.0035. [ABSTRACT FROM AUTHOR]

Bolted connections are often used in pultruded glass fiber reinforced polymer (GFRP) structures. Blind bolts, which require installation from one side only, become convenient when access is limited to tighten the ordinary bolts, especially for tubular GFRP sections. This paper presents the results of a comparative study on pultruded GFRP double-lap joints using ordinary bolts and blind bolts. Static experiments were conducted on pultruded GFRP double-lap joints with two columns of bolts, whereas the number of rows varied by one, two, and three. The static behaviors of ordinary bolted and blind bolted joints were compared in terms of load-displacement response, failure modes, and failure load. Then, constant amplitude fatigue tests were carried out on the double-lap joints with two bolts in a row. The maximum fatigue load varied from 30 to 80% of the static failure load of the corresponding joint. The fatigue life of each specimen was recorded and S-N curve was obtained. It was found that the static failure loads of blind bolted joints were lower by a maximum of 21% than those of ordinary bolted joints, whereas the fatigue performance was not much affected by the type of the bolts. [ABSTRACT FROM AUTHOR]