Ahmed K. El-Sayed

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.

Shear Capacity of High-Strength Concrete Beams Reinforced with FRP Bars

This paper reports experimental data on the behavior and shear strength of high-strength concrete slender beams reinforced with fiber-reinforced polymer (FRP) bars. Shear tests were conducted on six large-scale reinforced concrete beams without stirrups using high-strength concrete (f c = 65 MPa) along with three beams using normal-strength concrete (f c = 35 MPa). The beams measured 3250 mm long, 250 mm wide, and 400 mm deep, and were tested in four-point bending. The test variables were strength of concrete, and the reinforcement ratio and modulus of elasticity of the longitudinal reinforcing bars. Carbon and glass FRP bars and conventional steel bars were used as longitudinal reinforcement in this investigation. The experimental shear strengths of the FRP-reinforced concrete beams were compared to theoretical predictions provided by ACI 440.1R-03 and the modified form of this method proposed by the authors. The test results indicated that the high-strength concrete beams exhibited slightly lower relative shear strength compared to normal-strength concrete beams. In addition, the ACI 440.1R-03 design method provided very conservative predictions whereas the proposed modified equation gave better results.

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.

Evaluation of the new Canadian highway bridge design code shear provisions for concrete beams with fiber-reinforced polymer reinforcement

The Canadian highway bridge design code (CHBDC) contains provisions for designing concrete members with fiber-reinforced polymer (FRP) reinforcement. In the second edition of the code, new shear design procedures for FRP-reinforced sections are provided. These procedures are consistent with those for steel-reinforced members in the code, in consideration of some modifications that account for the substantial differences between FRP and steel reinforcement. The shear approach adopted in the CHBDC follows the traditional approach of Vcxa0+ Vs for shear design. This paper presents an evaluation of this approach by comparing it with experimental shear strengths of available test data on beams longitudinally reinforced with FRP bars and with or without FRP stirrups. In addition, the CHBDC approach was compared with the FRP shear design provisions currently in effect in North America using the available test results. The comparison shows that the CHBDC method significantly underestimates the shear strength of FRP...

Shear Strength of Concrete Beams Reinforced with FRP Bars: Design Method

Synopsis: ACI Committee 440 has proposed a design approach for evaluating the concrete contribution to the shear resistance of FRP-reinforced concrete beams that accounts for the axial stiffness of FRP longitudinal reinforcement. Recent shear tests conducted on beams longitudinally reinforced with different types and ratios of FRP bars indicate that the current ACI 440.1R-03 shear design approach significantly underestimates the concrete shear strength of such beams. This paper presents a proposed modification to the ACI 440.1R-03 shear design equation. The proposed equation was verified against experimental shear strengths of 98 specimens tested to date, and the calculated values are shown to compare well. In addition, the proposed equation was compared to the major design provisions using the available test results. Better and consistent predictions were obtained using the proposed equation.

Behavior of Wide Shallow RC Beams Strengthened with CFRP Reinforcement

One-way reinforced concrete joist floors with wide shallow beams (WSBs) are used widely in building construction throughout the Middle East. The short- and long-term behavior of WSBs externally strengthened with carbon fiber-reinforced polymer (CFRP) reinforcement was studied on isolated beams and as part of full-scale building. This paper presents the results of the experimental investigation on the flexural performance of isolated WSBs externally strengthened with CFRP reinforcement. A total of six full-scale beams were constructed and tested to failure. The test variables were the amount, type, configuration, and the elastic modulus of CFRP reinforcement. The test results were presented in terms of deflections, ultimate capacities and modes of failure, crack width development, and strains in reinforcement and concrete. The test results showed significant improvement in the flexural performance of the strengthened beams with respect to flexural capacity, flexural stiffness, and crack width. All but one of the strengthened beams failed because of the debonding of CFRP reinforcement; however, the load carrying capacity of WSBs were more than that predicted by relevant design guidelines.

Crack Width Prediction for Concrete Beams Strengthened with Carbon FRP Composites

AbstractStrengthening of RC beams and slabs using fiber-reinforced polymers (FRPs) is known to control crack width. However, no specific provisions are provided by most international design codes f...

Efficiency of CFRP Strengthening in Controlling the Deflection of RC Beams in a Redundant Structural System

AbstractOne-way reinforced concrete joist floor with wide shallow beams (WSBs) are used widely in building construction throughout the Middle East. Situations arise when it is desirable to strengthen a specific member or a group of members in a floor to reduce their deflections. Extensive work has been made on the strengthening of isolated members using fiber-reinforced polymers (FRP) for providing much needed data on the member performance and characteristics where the ultimate goal is to apply these findings to actual complex existing structures. Judging by studies on individual isolated members strengthened with FRP, a substantial improvement in deflection control is expected. However, this cannot be directly applied to members in redundant structural systems before confirming that experimentally. This paper presents the results of an investigation on the effectiveness of carbon FRP (CFRP) external strengthening for the purpose of reducing deflection of WSBs as part of joist floor of a prototype reinfo...