Ehab El-Salakawy

Shear Strength of FRP-Reinforced Concrete Beams without Transverse Reinforcement

This paper studied the behavior and shear strength of concrete slender beams reinforced with fiber-reinforced polymer (FRP) bars. Nine large-scale reinforced concrete beams without stirrups were constructed and tested to failure. The beams measured 3250 mm long, 250 mm wide, and 400 mm deep and were tested in 4-point bending. Test variables were the reinforcement ratio and modulus of elasticity of the longitudinal reinforcing bars. The test beams included 3 reinforced with glass FRP bars, 3 reinforced with carbon FRP bars, and 3 control beams reinforced with conventional steel bars. Test results were compared with predictions provided by the different available codes, manuals, and design guidelines, indicating that the relatively low modulus of elasticity of FRP bars results in reduced shear strength compared to that of control beams reinforced with steel. The current ACI 440.1R design method offered very conservative predictions, particularly for beams reinforced with glass FRP bars. Based on obtained experimental results, a proposed modification to the current ACI 440.1R design equation is given and verified against test results from other research.

Bond Performance of Near-Surface-Mounted FRP Bars

Near-surface-mounted (NSM) reinforcement has become a well-known method for strengthening existing concrete structures. The bond between the NSM reinforcing bars and concrete is the key factor in the NSM technique. In the NSM technique, there are two bond interfaces: one between the NSM bar and the adhesive, and the other between the adhesive and the concrete. For this technique to perform efficiently, these two interfaces need to be investigated. On the other hand, concrete structures that require rehabilitation are often exposed to aggressive environments. Many of these environments are related to cold-climate conditions as can be found in Canada. Environmental factors including freeze/thaw action, exposure to deicing salts, and sustained low temperatures combine to attack the integrity of repaired structures. Consequently, repair materials for the Canadian infrastructure must be able to withstand these harsh conditions for prolonged periods of time. A total of 80 NSM-fiber-reinforced polymer (FRP) bars installed in C-shaped concrete specimens were tested in pull-out setup to failure. Sixty specimens were tested at normal room temperature, while the remaining 20 specimens were tested after conditioning in an environmentally controlled chamber for 200 freeze/thaw cycles. The dimensions of the specimens were designed, upon a preliminary phase of testing, to ensure that no transverse cracking would occur in the specimen before bond failure of the NSM bar. The results are presented in term of failure load, average bond stress, strains in FRP bar, end slip, and mode of failure. A bond-slip model was proposed for the used FRP bars.

Durability of GFRP Bars’ Bond to Concrete under Different Loading and Environmental Conditions

In the last decade, noncorrodible fiber-reinforced polymer (FRP) reinforcing bars have been increasingly used as the main reinforcement for concrete structures in harsh environments. Also, owing to their lower cost compared with other types of FRP bars, glass-FRP (GFRP) bars are more attractive to the construction industry, especially for implementation in bridge deck slabs. In North America, bridge deck slabs are exposed to severe environmental conditions, such as freeze-thaw action, in addition to traffic fatigue loads. Although the bond strength of GFRP bars has been proved to be satisfactory, their durability performance under the dual effects of fatigue-type loading and freeze-thaw action is still not well understood. Few experimental test data are available on the bond characteristics of FRP bars in concrete elements under different loading and environmental conditions. This research investigates the individual and combined effects of freeze-thaw cycles along with sustained axial load and fatigue loading on the bond characteristics of GFRP bars embedded in concrete. An FRP-reinforced concrete specimen was developed to apply axial-tension fatigue or sustained loads to GFRP bars within a concrete environment. A total of thirty-six test specimens was constructed and tested. The test parameters included bar diameter, concrete cover thickness, loading scheme, and environmental conditioning. After conditioning, each specimen was sectioned into two halves for pullout testing. Test results showed that fatigue load cycles resulted in approximately 50% loss in the bond strength of sand-coated GFRP bars to concrete, while freeze-thaw cycles enhanced their bond to concrete by approximately 40%. Larger concrete covers were found more important in cases of larger bar sizes simultaneously subjected to fatigue load and freeze-thaw cycles.

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 conti...

Serviceability of Concrete Bridge Deck Slabs Reinforced with Fiber-Reinforced Polymer Composite Bars

Serviceability concerns, especially cracking and deflection, usually govern the design of reinforced concrete flexural members reinforced with fiber-reinforced polymer (FRP) bars. This work aimed to investigate the flexural behavior and serviceability performance of concrete deck slabs reinforced with different types of FRP composite bars. A total of 10 full-size, 1-way concrete slabs were constructed and tested. The slabs were 3100 mm long x 1000 mm wide x 200 mm deep. The test parameters were type and size of FRP reinforcing bars and the reinforcement ratio. Five slabs were reinforced with glass FRP (GFRP), 3 were reinforced with carbon FRP (CFRP) bars, and 2 control slabs were reinforced with conventional steel. The slabs were tested under 4-point bending over a simply supported clear span of 2500 and a shear span of 1000 mm. The test results are reported in terms of deflection, crack width, strains in concrete and reinforcement, ultimate capacity, and mode of failure. Comparison with the predictions of CAN/CSA-S806-02, CAN/CSA-S6-00 codes, and ACI 440.1R-01 design guidelines is also presented. Test results show that slabs with a CFRP or GFRP reinforcement ratio equivalent to the balanced reinforcement ratio satisfy serviceability and strength requirements of the considered design codes.

Bend Strength of FRP Stirrups: Comparison and Evaluation of Testing Methods

This paper provides a comparison and evaluation of the current test methods used to determine the strength of fiber-reinforced polymer FRP bent bars/stirrups at the bend location bend strength. The available methods depend on applying tensile forces through the straight portion of the bent bar/stirrup and keeping the bend zone restrained to generate a stress perpendicular to the bend direction in addition to the stress in the longitudinal direction. This could be achieved through the ACI 440.3R-04 B.12 test method for U-shaped bare FRP bars. Another possible method is the ACI 440.3R-04 B.5 which evaluates the bend strength of FRP stirrups by embedding them in two concrete blocks, which are pushed apart until the rupture of the FRP bent bars. Both methods were employed in testing FRP stirrups and bent bars and the bend strength was compared. The test results showed that the ACI 440.3R-04 B.12 test method consistently underestimates the bend strength of FRP stirrups. On the other hand, B.5 test method is more reliable and representative to the actual state of stresses in real concrete structural elements.

Shear Performance of RC Bridge Girders Reinforced with Carbon FRP Stirrups

One of the main components in girder-type bridges is bridge girder. This paper presents experimental data on the behavior and shear strength of concrete bridge girders reinforced with carbon fiber-reinforced polymer CFRP stirrups. A total of four large-scale reinforced concrete beams with a total length of 7,000 mm and a T-shaped cross section were constructed and tested up to failure. The test variables were the type and ratio of shear reinforcement stirrups. The test beams included three beams reinforced with sand-coated CFRP stirrups of 9.5-mm-diameter spaced at d /2, d /3, and d /4 where d is the beam depth and a control beam reinforced with conventional steel stirrups of 9.5-mm-diameter spaced at d /2. The geometry of the test prototypes were selected to simulate the New England Bulb Tee NEBT beams that are being used by the Ministry of Transportation of Quebec, Canada. As designed, three beams failed in shear due to CFRP stirrup rupture or steel stirrup yielding. While, the forth one, reinforced with CFRP stirrups spaced at d /4, failed in flexure due to yielding of longitudinal reinforcement. The test results were compared to predictions provided by different codes and design guidelines. The current ACI 440.1R-06 design method provides conservative predictions; however, the CAN/CSA S6-06 and JSCE 1997 underesti- mate the contribution of the FRP stirrups due to low strain limits.

Behavior of concrete bridge deck slabs reinforced with fiber-reinforced polymer bars under concentrated loads

While the expansive corrosion of steel reinforcement is a major concern in reinforced concrete bridge deck slabs, the noncorrosive fiber-reinforced polymer (FRP) composite bars provide an excellent alternative reinforcement. In this paper, the behavior of edge-restrained concrete bridge deck slabs reinforced with glass FRP and carbon FRP bars was investigated. Six full-scale deck slabs 3000 mm long x 2500 mm wide x 200 mm deep were constructed and tested to failure in the laboratory. Three deck slabs were reinforced with glass FRP (GFRP) bars, two deck slabs were reinforced with carbon FRP (CFRP) bars, and the remaining slab was reinforced with steel bars as control. The test parameters were the reinforcement type and ratio in the bottom transverse direction. The deck slabs were supported on two steel girders spaced at 2000 mm center-to-center and were subjected to a monotonic single concentrated load over a contact area of 600 x 250 mm to simulate the footprint of sustained truck wheel load (87.5 kN CL-625 truck) acting on the center of each slab. The experimental results were presented in terms of cracking, deflection, strains in concrete and reinforcement, ultimate capacity, and mode of failure. It was observed that the mode of failure for all deck slabs was punching shear with carrying capacities of more than three times the design factored load specified by the Canadian Highway Bridge Design Code. It was also concluded that the maximum measured crack widths and deflections at service load level were below the allowable code limits. In addition, a new empirical model to predict the punching shear capacity of restrained FRP-reinforced bridge deck slabs was introduced and verified against the available models and experimental results of others researchers. The proposed model showed goad agreement with the available test results.

Performance Evaluation of Glass Fiber-Reinforced Polymer Shear Reinforcement for Concrete Beams

Using fiber-reinforced polymer (FRP) reinforcing bars as the main reinforcement for concrete structures in severe environments is becoming a widely accepted solution to overcome the problem of steel corrosion and the related deteriorations. Due to the relatively lower cost of glass FRP (GFRP) bars compared to the other commercially available FRP bars, the use of GFRP bars in reinforced concrete (RC) structures has been widely investigated in the last few years. This paper reports experimental data on the shear strength of concrete beams reinforced with GFRP stirrups. A total of four large-scale RC beams with a total length of 7000 mm (276 in.) and a T-shaped cross section were constructed and tested up to failure. The test variables were type and ratio of shear reinforcement (stirrups). The test beams comprised three beams reinforced with sand-coated GFRP stirrups of 9.5 mm (3/8 in.) diameter spaced at d/2, d/3, and d/4 (where d is the beam depth), and a reference beam reinforced with conventional steel stirrups of 9.5 mm (3/8 in.) diameter spaced at d/2. As designed, the beams failed in shear due to GFRP stirrup rupture or steel stirrups yielding. ACI 440.1R-06 and the updated version of CAN/CSA S6-06 are able to predict the shear strength of beams reinforced with GFRP stirrups with a reasonable accuracy. The analytical approach using Response 2000 (R2K), which is based on the modified compression field theory (MCFT), predicted well the shear capacity of the beams reinforced with GFRP stirrups, but overestimated their shear crack width.

CONCRETE BRIDGE BARRIERS REINFORCED WITH GLASS FIBER-REINFORCED POLYMER COMPOSITE BARS

Recent expansion of highway networks has increased the need to provide corrosion-free reinforced concrete components for highway bridges. This paper describes an extensive research program that investigated the behavior of 2 types of bridge barriers--PL-2 and PL-3--reinforced with glass fiber-reinforced polymer (GFRP) bars. The geometry, concrete dimensions, and reinforcement of both PL-2 and PL-3 barriers were based on the new Canadian Highway Bridge Design Code. Sand-coated GFRP bars and conventional steel bars were used in the experimental study. The performance of barriers reinforced with GFRP bars was evaluated and compared with that of their counterparts reinforced with steel. Results indicate that the behavior of PL-2 and PL-3 concrete bridge barriers reinforced with GFRP bars is very similar to their counterparts reinforced with conventional steel in terms of cracking, deflections, strains, energy absorption, integrity, and ultimate strength.