Flexural Strength of RC Beams with GFRP Laminates

The results of an experimental and numerical study of the flexural behavior of reinforced concrete beams strengthened with glass-fiber-reinforced-polymer (GFRP) laminates are presented in this paper. In the experimental program, ten strengthened beams and two unstrengthened beams are tested to failure under monotonic loading. A number of external GFRP laminate layers and bond length of GFRP laminates in shear span are taken as the test variables. Longitudinal GFRP strain development and interfacial shear stress distribution from the tests are examined. The experimental results generally showed that both flexural strength and stiffness of reinforced concrete beams could be increased by such a bonding technique. In the numerical study, an eight-node interface element is developed to simulate the interface behavior between the concrete and GFRP laminates. This element is implemented into the MARC software package for the finite-element analyses of GFRP laminate strengthened reinforced concrete beams. Reasonably good correlations between experimental and numerical results are achieved.     

Flexural Behavior of Continuous GFRP Reinforced Concrete Beams

The results of testing two simply and three continuously supported concrete beams reinforced with glass fiber-reinforced polymer (GFRP) bars are presented. The amount of GFRP reinforcement was the main parameter investigated. Over and under GFRP reinforcements were applied for the simply supported concrete beams. Three different GFRP reinforcement combinations of over and under reinforcement ratios were used for the top and bottom layers of the continuous concrete beams tested. A concrete continuous beam reinforced with steel bars was also tested for comparison purposes. The experimental results revealed that over-reinforcing the bottom layer of either the simply or continuously supported GFRP beams is a key factor in controlling the width and propagation of cracks, enhancing the load capacity, and reducing the deflection of such beams. Comparisons between experimental results and those obtained from simplified methods proposed by the ACI 440 Committee show that ACI 440.1R-06 equations can reasonably predict the load capacity and deflection of the simply and continuously supported GFRP reinforced concrete beams tested.     

Flexural Behavior of Concrete Beams Reinforced with Hybrid (GFRP and Steel) Bars

Reinforcing concrete with a combination of steel and glass fiber-reinforced polymer (GFRP) bars promises favorable strength, serviceability, and durability. To verify its promise and to support design of concrete structures with this hybrid type of reinforcement, we have experimentally and theoretically investigated the load-deflection behavior of concrete beams reinforced with hybrid GFRP and steel bars. Eight beams, including two control beams reinforced with only steel or only GFRP bars, were tested. The amount of reinforcement and the ratio of GFRP to steel were the main parameters investigated. Hybrid GFRP/steel-reinforced concrete beams with normal effective reinforcement ratios exhibited good ductility, serviceability, and load carrying capacity. Comparisons between the experimental results and the predictions from theoretical analysis showed that the models we adopted could adequately predict the load carrying capacity, deflection, and crack width of hybrid GFRP/steel-reinforced concrete beams.     

Shear Strength of Normal Strength Concrete Beams Reinforced with Deformed GFRP Bars

This paper evaluates the shear strength, Vc, of intermediate length (2.5 < a∕d < 6) simply supported concrete beams subjected to four-point monotonic loading and reinforced with deformed, glass fiber-reinforced polymer (GFRP) reinforcement bars. Six different overreinforced GFRP designs, ρ > ρb, were tested with three replicate beams per design. All samples failed as a result of diagonal-tension shear. Measured shear strengths at failure are compared with theoretical predictions calculated according to traditional steel-reinforced concrete procedures and recently published expressions intended for beams reinforced with GFRP. Recommendations are made regarding the adequacy of shear strength prediction equations for GFRP-reinforced members. The study concludes that shear capacity is significantly overestimated by the “Building Code Requirements for Structural Concrete and Commentary” (ACI 318-99) expression for, Vc, as a result of the large crack widths, small compression block, and reduced dowel action in GFRP-reinforced flexural members. Shear strength was found to be independent of the amount of longitudinal GFRP reinforcement. A simplified empirical equation for predicting the ultimate shear strength of concrete beams reinforced with GFRP is endorsed.     

Behavior and Ductility of Simple and Continuous FRP Reinforced Beams

The behaviors of simply and continuously supported beams reinforced with fiber reinforced polymer (FRP) materials are presented in this paper. The experimental testing program included seven simple rectangular beams and seven continuous T-section beams. Reinforcing bars and stirrups were made of steel, carbon, or glass fiber reinforced polymer (GFRP). It was concluded that the use of GFRP stirrups increased the shear deformation, and as a result deflection increased. Also, GFRP stirrups changed the failure mode from flexural to shear or flexural-shear, depending on the type of reinforcement bars (FRP or steel). Furthermore, the use of FRP reinforcement in continuous beams increased deformation. This increase remained small and acceptable at the service load level, but significantly increased near failure. While different FRP reinforcement arrangements were found to have the same load capacity as steel reinforcements in conventional beams, failure modes and ductility differed. Failure mode was governed by both the type of reinforcing bars and the type of stirrups. Additionally, the dowel effect influences the load carrying capacity of FRP reinforced continuous beams. A method for evaluating the ductility is presented. The ratio of absorbed energy at failure to the total energy, “energy ratio,” was used as a measure of ductility. Based on this definition, a classification of ductile, semiductile, and brittle behavior is suggested. The theoretical results obtained using the suggested method were substantiated experimentally. The continuous beams experienced higher “energy ratios” than did simple beams.     

Tests on Seismically Damaged Reinforced Concrete Walls Repaired and Strengthened Using Fiber-Reinforced Polymers

The behavior of six 1:2.5-scale reinforced concrete cantilever wall specimens having an aspect ratio of 1.5, tested to failure and subsequently repaired and strengthened using fiber-reinforced polymer (FRP) sheets is investigated. Specimens were first repaired by removing heavily cracked concrete, lap splicing the fractured steel bars by welding new short bars, placing new hoops and horizontal web reinforcement, and finally casting nonshrink high-strength repair mortar. The specimens were then strengthened using FRP sheets and strips, with a view to increasing flexural as well as shear strength and ductility. In addition to different arrangements of steel and FRP reinforcement in the walls, a key parameter was the way carbon-FRP strips added for flexural strengthening were anchored; steel plates and steel angles were used to this effect. Steel plates were anchored using U-shaped glass-FRP (GFRP) strips or bonded metal anchors. Test results have shown that by using FRP reinforcement, the flexural and shear strength of the specimens can be increased. From the anchorage systems tested, metal plates combined with FRP strips appear to be quite efficient. The effectiveness of the bonded metal anchors used was generally less than that of the combination of plates and GFRP strips. In all cases, final failure of the FRP anchorage is brittle, but only occurs after the peak strength is attained and typically follows the fracture of steel reinforcement in critical areas, hence the overall behavior of the strengthened walls is moderately ductile.     

Monte Carlo Simulation of Shear Capacity of URM Walls Retrofitted by Polyurea Reinforced GFRP Grids

A model proposed in the literature for the evaluation of the in-plane shear capacity of unstrengthened and strengthened concrete and clay brick unreinforced masonry (URM) walls was modified and calibrated following the results from an experimental research program. The tested walls were strengthened with grids made from glass fiber-reinforced polymer (GFRP) embedded within a rapid-setting sprayed polyurea. Various GFRP grid reinforced polyurea layouts were investigated, and consisted of strips oriented in either the vertical or horizontal direction and installed on one or both faces. The prediction models proposed in this paper were subsequently evaluated using a probabilistic Monte Carlo simulation (MCS) by considering the uncertainty and variability of the independent variables, which were assumed to follow a truncated normal distribution. Corroborated by the MCS, test results clearly show that the failure modes of the strengthened URM walls were affected by the strengthening scheme. Experimental and simulation results are presented and discussed in this paper.     

Mechanism of Bond Behavior of Concrete Beams Strengthened with Near-Surface-Mounted CFRP Rods

Bond tests were conducted on concrete beams strengthened with near-surface-mounted (NSM) nonprestressed and prestressed carbon fiber-reinforced polymer (CFRP) rods under static loading. In the NSM technique, the CFRP rods are placed inside precut grooves and bonded to the concrete with epoxy adhesive. Six concrete beams were tested. The test variables included presence of internal tension steel reinforcement (unreinforced and reinforced), use of NSM CFRP strengthening (nonprestressed and prestressed), and type of CFRP rod (spirally wound and sand blasted). The beams were tested statically in four-point bending. Based on the test results, the transfer length for the prestressed CFRP rod in epoxied groove was 150 and 210 mm for the sand blasted and spirally wound rods, respectively. The main failure mode was debonding between the CFRP rod and the epoxy that starts at sections close to the midspan then, as the load increases, it propagates toward the supports. At failure, the beams strengthened with a given rod type showed the same CFRP strain at sections close to the support (29% of ultimate strain for spirally wound bars and 39% of ultimate strain for sand blasted bars). A cracked section analysis was carried out and compared well with the measured results.     

Behavior of Beams Strengthened with Novel Self-Anchored Near-Surface-Mounted CFRP Bars

A commonly observed failure mode in laboratory tests involving surface bonded fiber-reinforced polymer (FRP) laminates or near-surface-mounted (NSM) bars is premature delamination, that is, the separation of the FRP from the substrate well before the FRP reaches its ultimate strain capacity. To delay the onset of delamination and to ensure that the NSM FRP reinforcement continues to contribute to member strength after partial delamination, a new self-anchored carbon fiber-reinforced polymer (CFRP) bar was developed and tested for this investigation. This bar is made with a series of monolithic spikes that can be anchored deep inside the concrete. In addition to cutting grooves into the concrete cover for the placement of the primary reinforcing bar, holes are drilled deep into the concrete to insert the spikes. To test the performance of this bar, six large, simply supported, reinforced, concrete beams were retrofitted with NSM bars and tested in four-point bending. Two beams were strengthened with NSM bars without anchors or spikes but were otherwise similar to the self-anchored bar and served as control specimens (Series?B1). Two beams were strengthened in flexure with the new self-anchored NSM bars (Series?B2), and the remaining two beams (Series?B3) were strengthened in flexure and shear by using the self-anchored NSM bars as partial shear reinforcement. The effect of the proposed strengthening system on the beams’ strength, failure mode, deformability, and ductility are discussed on the basis of the experimental results. The anchors delayed delamination and enabled the NSM bar to experience at least a 77% higher strain at failure than the companion bar without anchors. The anchors also increased beam displacement ductility and energy ductility at a 20% strength degradation by at least 34% and 42%, respectively.     

Bond Performance of GFRP Bars in Tension: Experimental Evaluation and Assessment of ACI 440 Guidelines

The development/splice strength and the pullout local bond stress-slip response of glass fiber-reinforced polymer (GFRP) bars in tension were experimentally investigated using beam specimens and pullout specimens, respectively. Two types of 12-mm (0.47-in.)-diameter GFRP bars were evaluated, namely, thread wrapped and ribbed. The test parameters included the concrete cover, the splice length, and the area of steel confinement for the beam specimens, and the concrete compressive strength for the pullout specimens. Companion steel reinforced beams were also tested for comparison. All beam specimens reinforced with thread-wrapped GFRP bars experienced pullout mode of bond failure, while all specimens reinforced with ribbed GFRP bars or steel bars experienced splitting mode of bond failure. It was found that the bond strength of FRP bars is largely dependent on the surface conditions of the bars. The pullout local bond stress-slip response of ribbed GFRP bars is intrinsically similar to that of steel bars reported in the literature. The bond strength of both types of GFRP bars investigated was about two to three times lower than that of steel bars. Predictions of the development/splice strength of GFRP bars in accordance with the ACI Committee 440 guidelines were unconservative in comparison with the test data. Also, in contradiction with the current ACI 440 report, the use of transverse confining reinforcement increased the bond strength by a sizable 15–30%.     

Flexural Behavior of Continuous FRP-Reinforced Concrete Beams

Continuous concrete beams are commonly used elements in structures such as parking garages and overpasses, which might be exposed to extreme weather conditions and the application of deicing salts. The use of the fiber-reinforced polymers (FRP) bars having no expansive corrosion product in these types of structures has become a viable alternative to steel bars to overcome the steel-corrosion problems. However, the ability of FRP materials to redistribute loads and moments in continuous beams is questionable due to the linear-elastic behavior of such materials up to failure. This paper presents the experimental results of four reinforced concrete beams with rectangular cross section of 200×300?mm continuous over two spans of 2,800 mm each. The material and the amount of longitudinal reinforcement were the main investigated parameters in this study. Two beams were reinforced with glass FRP (GFRP) bars in to different configurations while one beam was reinforced with carbon FRP bars. A steel-reinforced continuous concrete beam was also tested to compare the results. The experimental results showed that moment redistribution in FRP-reinforced continuous concrete beams is possible if the reinforcement configuration is chosen properly. Increasing the GFRP reinforcement at the midspan section compared to middle support section had positive effects on reducing midspan deflections and improving load capacity. The test results were compared to the available design models and FRP codes. It was concluded that the Canadian Standards Association Code (CSA/S806-02) could reasonably predict the failure load of the tested beams; however, it fails to predict the failure location.     

Flexural Behavior of GFRP-Reinforced Concrete Masonry Beams

An experimental and analytical study is conducted in order to investigate the flexural behavior of masonry beams that are internally reinforced using glass fiber-reinforced polymers (GFRP) rebars. Seven reinforced masonry beams with 4.0- and 2.4-m spans were tested under four-point bending setup. The beams were loaded monotonically up to failure. One had two courses of hollow concrete masonry units and the remaining six beams had three courses. Two masonry beams were reinforced using conventional steel rebars and were considered as the control specimens. The remaining five beams were internally reinforced using GFRP rods with different reinforcement ratios. Beams were detailed to have sufficient shear reinforcement such that they do not fail in shear. Flexural capacity, deformation, curvature, and strains of the tested GFRP-reinforced and steel-reinforced masonry beams were compared and discussed. Using the acquired data from the experimental and analytical studies, effectiveness of GFRP rods as internal reinforcement for concrete masonry beams is demonstrated.     

Effect of Transverse Reinforcement on the Flexural Behavior of Continuous Concrete Beams Reinforced with FRP

Continuous concrete beams are structural elements commonly used in structures that might be exposed to extreme weather conditions and the application of deicing salts, such as bridge overpasses and parking garages. In such structures, reinforcing continuous concrete beams with the noncorrodible fiber-reinforced polymer (FRP) bars is beneficial to avoid steel corrosion. However, the linear-elastic behavior of FRP materials makes the ability of continuous beams to redistribute loads and moments questionable. A total of seven full-scale continuous concrete beams were tested to failure. Six beams were reinforced with glass fiber-reinforced polymer (GFRP) longitudinal bars, whereas one was reinforced with steel as control. The specimens have rectangular cross section of 200×300??mm and are continuous over two spans of 2,800?mm each. Both steel and GFRP stirrups were used as transverse reinforcement. The material, spacing, and amount of transverse reinforcement were the primary investigated parameters in this study. In addition, the experimental results were compared with the code equations to calculate the ultimate capacity. The experimental results showed that moment redistribution in FRP-reinforced continuous concrete beams is possible and is improved by increasing the amount of transverse reinforcement. Also, beams reinforced with GFRP stirrups illustrated similar performance compared with their steel-reinforced counterparts.     

Evaluation of Flexural Behavior and Serviceability Performance of Concrete Beams Reinforced with FRP Bars

Flexural behavior and serviceability performance of 24 full-scale concrete beams reinforced with carbon-, glass-, and aramid-fiber-reinforced-polymer (FRP) bars are investigated. The beams were 3,300?mm long with a rectangular cross section of 200?mm in width and 300?mm in depth. Sixteen beams were reinforced with carbon-FRP bars, four beams were reinforced with glass-FRP bars, two beams were reinforced with aramid-FRP bars, and two were reinforced with steel, serving as control specimens. Two types of FRP bars with different surface textures were considered: sand-coated bars and ribbed-deformed bars. The beams were tested to failure in four-point bending over a clear span of 2,750?mm. The test results are reported in terms of deflection, crack-width, strains in concrete and reinforcement, flexural capacity, and mode of failure. The experimental results were compared to the available design codes.     

Effectiveness of GFRP Sheets for Shear Strengthening of Timber

The objective of this study was to develop a cost-effective shear-strengthening technique for timber stringers that is environmentally friendly and leads to a durable structure. Testing was performed on creosote-treated Douglas fir beams, with dimensions of 100×400×3,650?mm, removed from a 40 year old bridge. Two strengthening schemes were investigated; incorporating vertical and diagonal glass fiber-reinforced polymer (GFRP) sheets applied to both shear spans. The diagonal scheme proved effective in increasing the average ultimate load, flexural stiffness, and deformability of the beams. Performance of the members reinforced using the vertical scheme, however, was poor compared to diagonally reinforced beams. The contribution of the diagonal sheets to the shear capacity of the stringers was around 12% at service loads and 40% at ultimate load. In conclusion, this study has shown that diagonal GFRP sheets are more effective than vertical sheets in shear-strengthening timber stringers with horizontal splits at their ends.     

Strengthening of Interior Slab–Column Connections Using a Combination of FRP Sheets and Steel Bolts

The results of an experimental investigation undertaken to evaluate a new technique for strengthening interior slab–column connection in combined flexural and shear modes are presented. The technique consists of using a combination of shear bolts inserted into holes and prestressed against the concrete surface for improving the punching shear capacity, and external [fiber-reinforced polymer (FRP)] reinforcement bonded to the tension face of the slabs in two perpendicular directions for increasing the flexural strength of the slabs. Square slab specimens of 670×670?mm dimensions were tested and the main test variables included the ratio of steel reinforcement (1.0 and 1.5%), span–depth ratio or thickness (55 and 75?mm) of the slabs, area, and configuration of steel bolts, and area of FRP reinforcement. It was found that the use of shear bolts alone improves the punching shear strength and increases the ductility of failure by changing the failure mode from punching to flexural. However, the use of a combination of shear bolts and a moderate amount of FRP reinforcement increased the flexural strength and resulted in a substantial improvement of the punching shear capacity of the slabs. The corresponding increases attained levels between 34 and 77%. A design approach is presented for evaluating the ultimate capacity of the slab–column connections when strengthened using the proposed strengthening technique. Strength results predicted by the proposed approach were in good agreement with the experimental results.     

Fatigue Flexural Behavior of Corroded Reinforced Concrete Beams Repaired with CFRP Sheets

This study investigated the flexural behavior of corroded steel reinforced concrete beams repaired with carbon-fiber-reinforced polymer (CFRP) sheets under repeated loading. Thirty beams (152×254×2,000?mm) were constructed and tested. Fatigue flexural failure occurred in 29 of these beams. The study showed that pitting of the steel reinforcement due to corrosion occurred only after about a 7% actual mass loss which coincided with a decrease in the fatigue performance of the beam. The controlling factor for the fatigue strength of the beams is the fatigue strength of the steel bars. Repairing with CFRP sheets increased the fatigue capacity of the beams with corroded steel reinforcement beyond that of the control unrepaired beams with uncorroded steel reinforcement. Beams repaired with CFRP at a medium corrosion level and then further corroded to a high corrosion level before testing had a comparable fatigue performance to those that were repaired and tested after corroding directly to a high corrosion level.     

Bond Strength of Tension Lap Splices in High-Strength Concrete Beams Strengthened with Glass Fiber Reinforced Polymer Wraps

This paper presents the experimental results of the first phase of a study undertaken at the American University of Beirut to examine the effectiveness of fiber reinforced polymer (FRP) wraps to confine steel reinforcement in a tension lap splice region anchored in high-strength reinforced-concrete beams. Seven beam specimens were constructed. The specimens were reinforced on the tension side with three deformed bars spliced at midspan. The splice region was devoid of any transverse reinforcement to allow a full examination of the FRP wrap contribution. Glass fiber reinforced polymer (GFRP) sheets were used. The main test variables were the GFRP configuration in the splice region (one strip, two strips, or a continuous strip), and the number of layers of the GFRP wraps placed around the splice region (one layer or two layers). All GFRP wraps were U-shaped. Except for the epoxy adhesive, no other anchorage mechanism or bonding procedure was applied for the GFRP wraps on the concrete beam. Following the application of the GFRP wraps, the beams were tested in positive bending. The test results demonstrated that GFRP wraps were effective in enhancing the bond strength and ductility of failure mode of the tension lap splices, especially when continuous strips were applied over the splice region.     

Flexural Behavior of Reinforced Concrete Beams Strengthened with CFRP Sheets and Epoxy Mortar

Experiments were conducted to study the effect of using epoxy mortar patch end anchorages on the flexural behavior of reinforced concrete beams strengthened with carbon fiber-reinforced polymer (CFRP) sheets. More specifically, the effect of the end anchorage on strength, deflection, flexural strain, and interfacial shear stress was examined. The test results show that premature debonding failure of reinforced concrete beams strengthened with CFRP sheet can be delayed or prevented by using epoxy mortar patch end anchorages. A modified analytical procedure for evaluating the flexural capacity of reinforced concrete beams strengthened with CFRP sheets and epoxy mortar end anchorage is developed and provides a good prediction of test results.     

Flexural Reinforcement of Glulam Timber Beams and Joints with Carbon Fiber-Reinforced Polymer Rods

Fiber-reinforced polymer (FRP) composites have largely been used in combination with masonry and concrete structural elements in the last decade. Recent applications showed that new advantages may also be achieved in the field of timber structures, even if currently steel fasteners are used mainly in connecting systems. This study investigated the possibility of using carbon FRP (CFRP) rods as glued-in reinforcement of glulam beams and as glued-in connectors for glulam timber head joints that should transfer flexural moment between two adjacent beams. Half-scale beams were tested both with and without the presence of FRP reinforcement. Flexural behavior of CFRP-reinforced beams was compared with unreinforced beams that were used as control specimens. Two different amounts of CFRP reinforcement were used in the beam section. Experimental results showed a significant influence of the CFRP rods, because the reinforced beams demonstrated an increase in ultimate capacity and stiffness. Experimental results were also compared with numerical analysis, which showed good accordance with regard to the load and deflection values. Full-size head joints were prepared and tested. Flexural behavior of the joints was compared with the mechanical properties of monopiece beams that were used as reference specimens. Three different force transfer lengths were used for the construction of CFRP-timber joints. Experimental results showed that the use of CFRP rods in timber joints was successful, because the capacity of the CFRP-jointed beams was almost the same as that of the monolithic beams for the longest bond length that was adopted. This result is important in order to find an adequate alternative to traditional joints made with steel bolts and plates, which are unable to create rigid connections, increase dramatically the weight of timber structures, and may be subjected to corrosion in an aggressive environment. A numerical modeling based on the virtual work principle was also conducted and theoretical results were found in good accordance with the experimental results for the tested joint.