Showing papers in "Journal of Composites for Construction in 2003"

Durability Gap Analysis for Fiber-Reinforced Polymer Composites in Civil Infrastructure

Abstract: The lack of a comprehensive, validated, and easily accessible data base for the durability of fiber-reinforced polymer (FRP) composites as related to civil infrastructure applications has been identified as a critical barrier to widespread acceptance of these materials by structural designers and civil engineers. This concern is emphasized since the structures of interest are primarily load bearing and are expected to remain in service over extended periods of time without significant inspection or maintenance. This paper presents a synopsis of a gap analysis study undertaken under the aegis of the Civil Engineering Research Foundation and the Federal Highway Administration to identify and prioritize critical gaps in durability data. The study focuses on the use of FRP in internal reinforcement, external strengthening, seismic retrofit, bridge decks, structural profiles, and panels. Environments of interest are moisture/solution, alkalinity, creep/relaxation, fatigue, fire, thermal effects (including free...

Comparative Study of Models on Confinement of Concrete Cylinders with Fiber-Reinforced Polymer Composites

Abstract: The use of fiber-reinforced polymer (FRP) composites for strengthening and/or rehabilitation of concrete structures is gaining increasing popularity in the civil engineering community. One of the most attractive applications of FRP materials is their use as confining devices for concrete columns, which may result in remarkable increases of strength and ductility as indicated by numerous published experimental results. Despite a large research effort, a proper analytical tool to predict the behavior of FRP-confined concrete has not yet been established. Most of the available models are empirical in nature and have been calibrated against their own sets of experimental data. On the other hand, the experimental results available in the literature encompass a wide range of values of the significant variables. The objective of this work is a systematic assessment of the performance of the existing models on confinement of concrete columns with FRP materials. The study is conducted in the following steps: the experimental data on confinement of concrete cylinders with FRP available in the technical literature are classified according to the values of the significant variables; the existing empirical and analytical models are reviewed, pointing out their distinct features; the whole set of available experimental results is compared with the whole set of analytical models; strengths and weaknesses of the various models are analyzed. Finally, a new equation is proposed to evaluate the axial strain at peak stress of FRP-confined concrete cylinders.

Experimental investigation of frp-strengthened rc beam-column joints

Abstract: The results of a comprehensive experimental program, aimed at providing a fundamental understanding of the behavior of shear-critical exterior reinforced concrete (RC) joints strengthened with fiber reinforced polymers (FRP) under simulated seismic load, are presented in this study. The role of various parameters on the effectiveness of FRP is examined through 2/3-scale testing of 18 exterior RC joints. Conclusions are drawn on the basis of certain load versus imposed displacement response characteristics, comprising the strength (maximum lateral load), the stiffness, and the cumulative energy dissipation capacity. The results demonstrate the important role of mechanical anchorages in limiting premature debonding, and they provide important information on the role of various parameters, including: area fraction of FRP; distribution of FRP between the beam and the column; column axial load; internal joint (steel) reinforcement; initial damage; carbon versus glass fibers; sheets versus strips; and effect of transverse beams.

Investigation of bond in concrete structures strengthened with near surface mounted carbon fiber reinforced polymer strips

Abstract: Fiber reinforced polymer (FRP) materials are currently produced in different configurations and are widely used for the strengthening and retrofitting of concrete structures and bridges. Recently, considerable research has been directed to characterize the use of FRP bars and strips as near surface mounted reinforcement, primarily for strengthening applications. Nevertheless, in-depth understanding of the bond mechanism is still a challenging issue. This paper presents both experimental and analytical investigations undertaken to evaluate bond characteristics of near surface mounted carbon FRP (CFRP) strips. A total of nine concrete beams, strengthened with near surface mounted CFRP strips were constructed and tested under monotonic static loading. Different embedment lengths were used to evaluate the development length needed for effective use of near surface mounted CFRP strips. A closed-form analytical solution is proposed to predict the interfacial shear stresses. The model is validated by comparing t...

Application of fiber reinforced polymer overlays to extend steel fatigue life

Abstract: An experimental and analytical study was conducted to investigate the effectiveness of applying carbon fiber reinforced polymer (CFRP) overlays to steel fatigue tension coupons to prolong fatigue life. Specimens were either notched or center hole specimens and tested in uniaxial tension. Variables studied were CFRP system, bond length, bond area, one and two sided applications, and applications prior or subsequent to crack propagation. Two sided applications were very effective, prolonging fatigue life by as much as 115%. Similar application of CFRP materials subsequent to crack propagation extended the remaining fatigue life by approximately 170% without any other means of crack arrest. The method therefore showed promise as both a preventive technique and repair method. The epoxy performance was critical to the effectiveness of the system, with all failures initiated by debonding of the CFRP. Overlays were most effective when the system was applied directly to the potential crack trajectory. One-sided a...

Performance of Axially Loaded Short Rectangular Columns Strengthened with Carbon Fiber-Reinforced Polymer Wrapping

Abstract: This paper presents results of a comprehensive experimental investigation on the behavior of axially loaded short rectangular columns that have been strengthened with carbon fiber-reinforced polymer (CFRP) wrap. Six series, a total of 90 specimens, of uniaxial compression tests were conducted on rectangular and square short columns. The behavior of the specimens in the axial and transverse directions is investigated. The parameters considered in this study are (1) the concrete strength; (2) the aspect ratio of the cross section; and (3) the number of CFRP layers. The findings of this research can be summarized as follows: The CFRP wrapping enhances the compressive strength and the ductility of both square and rectangular columns, but to a lesser degree than that of circular columns. The ultimate strength and the ductility of the CFRP confined concrete increase with increasing number of confining layers. The increase in strength and ductility is more significant for lower strength concrete, representing poor or degraded concrete, than for normal-to-high strength concrete; that is, the maximum gain in strength that can be achieved for 3 ksi concrete wrapped columns is approximately 90%, as compared to only 30% for 6 ksi concrete wrapped columns. The CFRP confining jacket must be sufficiently stiff to develop appropriate confining forces at relatively low axial strain levels. The gain in compressive strength obtained by the CFRP confined concrete depends mainly on the relative stiffness of the CFRP jacket to the axial stiffness of the column.

Retrofitting of Reinforced Concrete Beams with CARDIFRC

Abstract: A new retrofitting technique based on a material compatible with concrete is currently under development at Cardiff University. It overcomes some of the problems associated with the current techniques based on externally bonded steel plates and FRP (fiber-reinforced polymer) laminates which are due to the mismatch of their tensile strength and stiffness with that of the concrete structure being retrofitted. This paper will describe briefly the technology necessary for preparing high-performance fiber-reinforced concrete mixes (HPFRCC), designated CARDIFRC. They are characterized by high tensile/flexural strength and high energy-absorption capacity (i.e., ductility). The special characteristics of CARDIFRC make them particularly suitable for repair, remedial, and upgrading activities (i.e., retrofitting) of existing concrete structures. The promising results of several studies using CARDIFRC for retrofitting damaged concrete flexural members will be presented. It will be shown that damaged reinforced concrete beams can be successfully strengthened and rehabilitated in a variety of different retrofit configurations using precast CARDIFRC strips adhesively bonded to the prepared surfaces of the damaged beams. To predict the moment resistance and load-deflection response of the beams retrofitted in this manner an analytical model will be introduced, and the results of the computations will be compared with the test results to evaluate the accuracy of the model.

Physical Properties of Glass Fiber Reinforced Polymer Rebars in Compression

Abstract: Forty-five glass fiber reinforced polymer (GFRP) rebars were tested in compression to determine their ultimate strength and Young’s modulus. The rebars (or C-bars), produced by Marshall Industries Composites, Inc., had an outside diameter of 15 mm (#15 rebar), and unbraced lengths varying from 50 to 380 mm. A compression test method was developed to conduct the experiments. Three failure modes, that are directly related to the unbraced length of the rebar, are identified as crushing, buckling, and combined buckling and crushing. The crushing region represents the failure mode a GFRP rebar would experience when confined in concrete under compression. The experimental results showed that the ultimate compressive strength of the #15 GFRP rebar failing by crushing is approximately 50% of the ultimate tensile strength. Based on a very limited number of tests, in which strain readings were acceptable, Young’s modulus in compression was found to be approximately the same as in tension.

Flexural Behavior of R/C Beams Strengthened with Carbon Fiber Reinforced Polymer Sheets or Fabric

Abstract: Their resistance to electro-chemical corrosion, high strength-to-weight ratio, larger creep strain, fatigue resistance, and nonmagnetic and nonmetallic properties make carbon fiber reinforced polym...

Repair of damaged steel-concrete composite girders using carbon fiber-reinforced polymer sheets

Abstract: The aging infrastructure of the United States requires significant attention for developing new materials and techniques to effectively and economically revive this aging system. Damaged steel-concrete composite girders can be repaired and retrofitted by epoxy bonding carbon fiber-reinforced polymer (CFRP) laminates to the critical areas of tension flanges. This paper presents the results of a study on the behavior of damaged steel-concrete composite girders repaired with CFRP sheets under static loading. A total of three large-scale composite girders made of W355×13.6 A36 steel sections and 75-mm-thick by 910-mm-wide concrete slabs were prepared and tested. One, three, and five layers of CFRP sheet were used to repair the specimen with 25, 50, and 100% loss of the cross-sectional area of their tension flange, respectively. The test results showed that epoxy bonded CFRP sheet could restore the ultimate load-carrying capacity and stiffness of damaged steel-concrete composite girders. Comparison of the experimental and analytical results revealed that the traditional methods of analysis of composite beams were conservative.

Punching Shear Behavior of Fiber Reinforced Polymers Reinforced Concrete Flat Slabs: Experimental Study

Abstract: This paper presents the results of a two-phase experimental program investigating the punching shear behavior of fiber reinforced polymer reinforced concrete (FRP RC) flat slabs with and without carbon fiber reinforced polymer (CFRP) shear reinforcement. In the first phase, problems of bond slip and crack localization were identified. Decreasing the flexural bar spacing in the second phase successfully eliminated those problems and resulted in punching shear failure of the slabs. However, CFRP shear reinforcement was found to be inefficient in enhancing significantly the slab capacity due to its brittleness. A model, which accurately predicts the punching shear capacity of FRP RC slabs without shear reinforcement, is proposed and verified. For slabs with FRP shear reinforcement, it is proposed that the concrete shear resistance is reduced, but a strain limit of 0.0045 is recommended as maximum strain for the reinforcement. Comparisons of the slab capacities with ACI 318-95, ACI 440-98, and BS 8110 punching shear code equations, modified to incorporate FRP reinforcement, show either overestimated or conservative results.

Reinforced Concrete T-Beams Strengthened in Shear with Fiber Reinforced Polymer Sheets

Abstract: This research studies the interaction of concrete, steel stirrups, and external fiber reinforced polymer (FRP) sheets in carrying shear loads in reinforced concrete beams. A total of eight tests were conducted on four laboratory-controlled concrete T-beams. The beams were subjected to a four-point loading. Each end of each beam was tested separately. Three types of FRP, uniaxial glass fiber, uniaxial carbon fiber, and triaxial glass fiber, were applied externally to strengthen the web of the T-beams, while some ends were left without FRP. The test results show that FRP reinforcement increases the maximum shear strengths between 15.4 and 42.2% over beams with no FRP. The magnitude of the increased shear capacity is dependent not only on the type of FRP but also on the amount of internal shear reinforcement. The triaxial glass fiber reinforced beam exhibited more ductile failure than the other FRP reinforced beams. This paper also presents a test model that is based on a rational mechanism and can predict the experimental results with excellent accuracy.

Behavior of concrete beams strengthened with fiber-reinforced polymer laminates under impact loading

Abstract: Most of the research on application of composite materials in civil engineering during the past decade has concentrated on the behavior of structural elements under static loads. In engineering practice, there are many situations in which structures undergo impact or dynamic loading. In particular, the impact response of concrete beams strengthened with composite materials is of interest. This paper presents the results of an experimental investigation conducted to study the impact effects on concrete beams strengthened with fiber-reinforced polymer laminates. Two types of composite laminates, carbon and Kevlar, were bonded to the top and bottom faces of concrete beams with epoxy. Five beams were tested: two strengthened with Kevlar laminates, two strengthened with carbon laminates, and one unretrofitted beam as the control specimen. The impact load was applied by dropping a steel cylinder from a specified height onto the top face of the beam. The test results revealed that composite laminates significant...

Shear Strengthening of Interior Slab–Column Connections Using Carbon Fiber-Reinforced Polymer Sheets

Abstract: This paper presents the results of an experimental investigation undertaken to evaluate the punching shear capacity of interior slab–column connections, strengthened using flexible carbon fiber-reinforced polymer (CFRP) sheets. Sixteen square (670×670mm) slab–column connections with different slab thicknesses (55 and 75 mm) and reinforcement ratios (1 and 1.5%) were tested. Twelve specimens were strengthened using CFRP sheets and the remaining four specimens were kept as controls. Without strengthening, all specimens were designed to experience punching shear failure. The CFRP sheets were bonded to the tension face of the specimens in two perpendicular directions parallel to the internal ordinary steel reinforcement. The test results clearly demonstrate that using CFRP leads to significant improvements in the flexural stiffness, flexural strength, and shear capacity of beam–column connections. Depending on the content of the ordinary reinforcement, thickness of the slab, and area of CFRP sheet, the flexur...

Experimental investigation of bonded fiber reinforced polymer-concrete joints under cyclic loading

Abstract: The strengthening of reinforced concrete structures by means of externally bonded fiber reinforced polymers (FRPs) is becoming an attractive technique for upgrading existing structures. Although previous laboratory investigations have shown that the bending capacities of beams can be increased considerably with this strengthening technique, premature failure by debonding of the FRP reinforcement can often limit its effectiveness. To gain insight into debonding phenomena, various experimental and analytical investigations of the behavior of bonded FRP-to-concrete joints have been carried out. However, such studies have generally been limited to monotonic (“static”) loading conditions. In this paper, we present results from an experimental investigation of bonded FRP-to-concrete joints under \Icyclic\N loading. First, we describe the experimental setup and test parameters. Next experimental results for the effects of \Icyclic\N loading on slip at the FRP–concrete interface, crack opening, and strain profiles along the bonded FRP joint are presented and discussed. A power-law expression for the so-called “\IS–N\N” curves (cyclic stress ranges versus numbers of cycles to failure) is proposed, and the parameters in this expression are determined from the experimental data. The influence of various parameters such as bond length, bond width, and cyclic bond stress levels on fatigue behavior are discussed.

Analytical models for concrete confined with frp tubes

Abstract: Concrete columns encased in fiber-reinforced polymer (FRP) tubes offer an attractive solution to enhance behavior of concrete in terms of strength as well as ductility. Analytical models for development of stress-strain curves for concrete confined with FRP are proposed in this paper. The predicted stress-strain curves for confined concrete using the proposed models are compared with those of tests for concrete specimens confined with FRP. It is demonstrated that the proposed models predict the stress-strain behavior of confined concrete very well. Based on the confidence gained in the proposed models, the effects of using different fibers, the presence of voids, and the number of layers are established.

Bond between Carbon Fiber Reinforced Polymer Bars and Concrete. I: Experimental Study

Abstract: The bond characteristics of four different types of carbon fiber reinforced polymer ~CFRP! rebars ~or tendons! with different surface deformations embedded in lightweight concrete were analyzed experimentally. In a first series of tests, local bond stress-slip data, as well as bond stress-radial deformation data, needed for interface modeling of the bond mechanics, were obtained for varying levels of confining pressure. In addition to bond stress and slip, radial stress and radial deformation were considered fundamental variables needed to provide for configuration-independent relationships. Each test specimen consisted of a CFRP rebar embedded in a 76-mm-~3 in.!-diam, 102-mm-~4 in.!-long, precracked lightweight concrete cylinder subjected to a constant level of pressure on the outer surface. Only 76 mm ~3 in.! of contact were allowed between the rebar and the concrete. For each rebar type, bond stress-slip and bond stress-radial deformation relationships were obtained for four levels of confining axisymmetric radial pressure. It was found that small surface indentations were sufficient to yield bond strengths comparable to that of steel bars. It was also shown that radial pressure is an important parameter that can increase the bond strength almost threefold for the range studied. In a second series of tests, the rebars were pulled out from 152-mm- ~6 in.!-diam, 610-mm-~24 in.!-long lightweight concrete specimens. These tests were conduced to provide preliminary data for development length assessment and model validation ~Part II!. DOI: 10.1061/~ASCE!1090-0268~2003!7:2~154! CE Database subject headings: Bonding; Fiber reinforced polymers; Composite materials; Concrete; Structural reinforcement; Car- bon; Confinement; Bars.

Composite Reinforcement to Strengthen Existing Concrete Structures against Air Blast

Abstract: The Wright Laboratory Air Base Survivability Section has been studying the development, application, and effects of externally applied composite reinforcing materials. The strengthened facilities would be capable of surviving an air-blast load at relatively short stand-off distances (11–15 m). An agreement was reached with the Israeli officials to conduct full-scale explosive tests in Israel using 860 kg of TNT on structures that had been reinforced externally with composite reinforcing materials. The strengthening procedure employed in this study involved two types of material: (1) an autoclave-cured, three-ply, carbon fiber-epoxy laminate; and (2) a knitted biaxial E-glass fabric. The Air Base Survivability Section applied the composite materials in Israel after the facilities had been constructed using an epoxy adhesive to bond the composite materials to the concrete substrate. This provided a simple, effective, and quick method of retrofitting an existing structure. The free-field and reflected pressures and accelerations on the walls were measured. The results of these tests were considered successful, considering the fact that the externally reinforced walls suffered high displacements, yet did not fail. The pressure and impulse data indicate that both structures would have failed catastrophically without the externally applied composite reinforcing materials.

Use of Composite Reinforcement to Strengthen Concrete and Air-Entrained Concrete Masonry Walls against Air Blast

Abstract: Two concrete structures and three air-entrained concrete (AEC) masonry walls were subjected to two, high explosive detonations. The concrete structures were placed at a stand-off distance such that medium damage was expected. The stand-off distance of the AEC-masonry walls was reduced on each successive detonation until breaching occurred. The two concrete structures retrofitted with composite materials were subjected to air-blast loading at a stand-off distance of approximately 14.6 m. The structures were constructed such that each long side of the structure contained a wall retrofitted with a composite material and a wall left bare as a control. Both concrete structures exhibited less residual displacement on the walls strengthened with composite materials than the bare control walls.

Flexural Behavior and Deformability of Fiber Reinforced Polymer Prestressed Concrete Beams

Abstract: After a brief review of the ductility and deformability indices currently used in the design of concrete beams reinforced or prestressed with steel or fiber reinforced polymer (FRP) tendons, a new definition of a deformability index (factor) for prestressed concrete beams is proposed. The new factor is defined in terms of both a deflection factor and a strength factor. The deflection factor is the ratio of the deflection at failure to the deflection at first cracking, while the strength factor is the ratio of the ultimate moment (or load) to the cracking moment (or load). The proposed deformability factor is verified not only by test results obtained by the writer, but also by other test results available in the literature and it appears to be a suitable measurement of the deformability of concrete beams prestressed with either FRP tendons or steel tendons.

Corrosion of steel reinforcement in carbon fiber-reinforced polymer wrapped concrete cylinders

Abstract: The rehabilitation, repair, and strengthening of concrete structures has increased worldwide with a growing number of systems employing externally applied fiber-reinforced polymer (FRP) composites. However, the service life and effectiveness of FRP repair and strengthening techniques when applied to concrete in corrosive marine environments is still not well understood. This paper presents the results of an experimental study on the corrosion performance of embedded steel reinforcement in cylindrical reinforced concrete specimens with 13 different surface treatment options. Samples were subjected to an impressed current and a high salinity solution. Test variables included the type of epoxy, wrap fiber orientation, and the number of wrap layers. Samples were evaluated for corrosion activity by monitoring corrosion potentials and impressed current flow levels, and by examining reinforcement mass loss and concrete chloride content among samples. Test results indicated that FRP wrapped specimens had prolonge...

Cyclic Flexure Tests of Masonry Walls Reinforced with Glass Fiber Reinforced Polymer Sheets

Abstract: The research work reported here investigates the out-of-plane flexural behavior of masonry walls reinforced externally with glass fiber reinforced polymer (GFRP) sheets and subjected to cyclic loading. A full-scale test program consisting of eight wall specimens was conducted. Nine tests were performed, in which three parameters were studied. These included the level of compressive axial load, amount of internal steel reinforcement, and amount of externally bonded GFRP sheet reinforcement. Of the three parameters studied, varying the amount of GFRP sheets was the only parameter that significantly affected the behavior of the walls. The GFRP sheet reinforcement governed the linear response of the bending moment versus centerline deflection hysteresis. Increasing or decreasing the amount of GFRP sheet reinforcement either increased or decreased both the wall stiffness and the ultimate strength, respectively. Except for visible cracks, the walls maintained their structural integrity throughout the out-of-plane cyclic loading. The unloading/reloading paths for successive loading cycles were similar, indicating little degradation. Thus, the general behavior of the walls was very predictable. The system, therefore, could be used to advantageously rehabilitate older masonry structures that are inadequately reinforced to withstand seismic events. A simple model of the behavior is also presented to allow for the evaluation of the strength and deformation characteristics of these elements.

Long-term properties and transfer length of fiber-reinforced polymers

Abstract: This paper discusses the experimental results on properties and transfer length of the common types of fiber-reinforced polymer (FRP) tendons. Based on the experimental results, an equation is proposed for predicting the creep coefficient of aramid-based FRP (AFRP) tendons. The results show that the creep of carbon-based FRP (CFRP) is less than 0.2%. The test results show that the transfer length of CFRP is in the range of 300–800 mm and the concrete strength at transfer is one of the major factors affecting the transfer length of CFRP. A new factor accounting for the concrete strength is proposed for estimating the transfer length of CFRP tendons, and the verification is made for this equation. The transfer length was found to vary from 170 to 270 mm, which was 20–30 times the tendon diameter for these AFRP tendons. Despite the creep and shrinkage of concrete and the relaxation of the tendon itself, the range for transfer length did not vary with time.

Repair of Cracked Aluminum Overhead Sign Structures with Glass Fiber Reinforced Polymer Composites

Abstract: Transportation departments have been using aluminum overhead sign structures since the 1950s. It is well documented that cracks develop in the welds between diagonal and chord members due to fatigue stresses from wind-induced vibration of the slender members. The cracks propagate to complete failure of the members, which can cause collapse of the truss and inflict injuries. The original design of overhead sign structures did not consider fatigue as a limit state. In addition, field welding of aluminum structures for any possible repairs is prohibited. A repair method for the cracked aluminum welded connections between diagonals and chord members using glass fiber reinforced polymer composites (GFRPs) is proposed. The static load carrying capacity of the welded connection, and the cracked connection repaired with GFRP composites are established. The paper describes the surface preparation of the aluminum tubular members, and the architecture and application sequence of the GFRP composite to retrofit the connection. Experimental results are presented from static tests of welded aluminum connections, welded aluminum connections retrofitted with GFRP composites, and new aluminum connections that depend only on GFRP composite elements for their strength. The results from monotonic static tests carried out on cracked welded specimens from actual sign structures show that the retrofitted connection with GFRP reinforcement achieved 1.17 to 1.25 times the capacity of the welded aluminum connection without any visible cracks. This result, and the minimal traffic disruption anticipated in the actual field application, makes this retrofit method a good candidate for implementation.

Short Term Testing of Hybrid T Beam Made of New Prepreg Material

Abstract: The civil engineering industry is constantly striving for ways to improve design and construction technologies to obtain more efficient solutions to engineering problems. It has long been recognized that, in the area of construction that utilizes reinforced concrete beams, the region of the beam below the neutral axis (NA) is wasteful of material. The only function that the low tensile strength concrete has in this situation is to locate the steel rebars and protect them from aggressive environments. This latter property is not completely fulfilled since the concrete will crack in the zone where there is tension in the loaded beam and will allow aggressive substances to attack the steel. It is proposed in this paper that the zone of a T cross-sectional beam below the NA is removed and replaced by an advanced polymer composite (APC) material. Two designs of a T beam were analyzed: one in which the failure mode is by buckling of the web and one by shear failure in the bond along the interface between the co...

Long-term properties and transfer length of fiber-reinforced polymers

Abstract: This paper discusses the experimental results on properties and transfer length of the common types of fiber-reinforced polymer (FRP) tendons. Based on the experimental results, an equation is proposed for predicting the creep coefficient of aramid-based FRP (AFRP) tendons. The results show that the creep of carbon-based FRP (CFRP) is less than 0.2%. The test results show that the transfer length of CFRP is in the range of 300-800 mm and the concrete strength at transfer is one of the major factors affecting the transfer length of CFRP. A new factor accounting for the concrete strength is proposed for estimating the transfer length of CFRP tendons, and the verification is made for this equation. The transfer length was found to vary from 170 to 270 mm, which was 20-30 times the tendon diameter for these AFRP tendons. Despite the creep and shrinkage of concrete and the relaxation of the tendon itself, the range for transfer length did not vary with time.

Environmental Effects on the Short-Term Bond of Carbon Fiber-Reinforced Polymer (CFRP) Composites

Abstract: Carbon fiber reinforced polymers (CFRP) are being increasingly used in many structural applications due to their excellent mechanical and corrosion resistance characteristics. CFRP sheets and strips are being used to strengthen waterfront concrete structures, such as piers and wharves. The CFRP reinforcements are bonded to beams, piles, and decks using structural adhesives. Adhesive strength can be affected by both short-term and long-term environmental exposure. In the current study, short-term effects of temperature, moisture, and chloride content on the CFRP adhesion are evaluated using pull-off tests. Three structural adhesives were chosen to assess the effects of three different temperatures and four different relative humidities on the CFRP adhesion to concrete cubes. In the case of concrete piles exposed to marine conditions, the effect of superficial chloride content on the short-term bond strength was also investigated. It was shown that high relative humidity may reduce bond strength below acceptable levels.

Performance Evaluation of Reinforced Concrete Bridge Columns Wrapped with Fiber Reinforced Polymers

Abstract: This study investigates the performance of new bridge columns wrapped with fiber reinforced polymers (FRP) when exposed to aggressive environmental conditions. This has been accomplished through field monitoring and laboratory tests. As part of the field monitoring, temperature data were collected at various locations of bridge columns. In addition, visual inspection of two bridges was performed periodically for over a period of two years. No evidence of deterioration of the FRP wraps was detected during that period. Laboratory tests were performed to investigate how FRP wraps protect reinforced concrete columns from corrosion, and freeze–thaw laboratory tests were conducted to study the impact of temperature cycles on the mechanical behavior of FRP-wrapped columns. From the corrosion experimental tests, it was found that FRP provides excellent protection against aggressive agents (salty water or moisture) even when a single layer is used. Compression tests were conducted on specimens subjected to freeze–...

Filament-wound glass fiber reinforced polymer bridge deck modules

Abstract: The demand for the development of efficient and durable bridge decks is a priority for most of the highway authorities worldwide. This paper summarizes the results of an experimental program designed to study the behavior of an innovative glass fiber reinforced polymer (GFRP) bridge deck recently patented in Canada. The deck consisted of a number of triangular filament wound tubes bonded with epoxy resin. GFRP plates were adhered to the top and bottom of the tubes to create one modular unit. The experimental program, described in this paper, discusses the evolution of two generations of the bridge deck. In the first generation, three prototype specimens were tested to failure, and their performance was analyzed. Based on the behavior observed, a second generation of bridge decks was fabricated and tested. The performance was evaluated based on load capacity, mode of failure, deflection at service load level, and strain behavior. All decks tested exceeded the requirements to support HS30 design truck loads specified by AASHTO with a margin of safety. This paper also presents an analytical model, based on Classical Laminate Theory to predict the load-deflection behavior of the FRP decks up to service load level. In all cases the model predicted the deck behavior very well.

Experimental and analytical behavior of carbon fiber-based rods as flexural reinforcement

Abstract: This paper presents the results of an experimental and analytical comparison of a study on the flexural behavior of concrete beams reinforced with sandblasted carbon fiber-based composite rods. Twelve beams, including three control beams reinforced with steel, were tested for strength, deformation, and failure characteristics. Analytical comparisons included the generation of the theoretical strength and moment curvature relations. Experimental data from pullout tests indicated that bonding of sandblasted rods is not a major concern. However, excessive deformation in achieving the predicted moment capacity could be a limiting factor in the design of these beams.