International Concrete Abstracts Portal

The flexural strength and deflection of high-strength concrete beams reinforced with multiple layers of reinforcement and combinations of different reinforcement types (steel, GFRP, and CFRP bars) were evaluated experimentally and analytically. Three beam specimens, reinforced with a single type of reinforcement, and three other specimens, reinforced with a combination of different types of reinforcement, were constructed and tested. An investigation was performed on the influence of hybrid reinforcing with multiple layers of steel or FRP flexural reinforcements on load-carrying capacity, post cracking stiffness, cracking pattern, and ductility. The low post cracking stiffness, high deflection, deep crack propagation, large crack width, and low ductility of FRP bar-reinforced beams were controlled and improved by hybrid reinforcing with steel bars. The test results were compared with the cracking and ultimate moment predictions of ACI Code, and with the service deflection predictions of ACI 440.1R-06 and Bischoff. In addition, alternative service deflection prediction models for hybrid reinforced concrete beams with multiple layers of steel or FRP bars were proposed based on the effective moment of inertia approach of ACI 440.1R-06 and Bischoff.

The behavior of the bridge barriers reinforced with GFRP bars is being investigated in collaboration with Ministry of Transportation of Quebec (MTQ). The test prototypes included four MTQ Type 311 barrier prototypes and two MTQ Type 210 barrier prototypes. For the MTQ Type 311 barrier prototypes, two of them were reinforced with GFRP bars and the other two were reinforced with steel bars. For the MTQ Type 210 barrier prototypes, one was reinforced with GFRP bars and the other one was reinforced with steel bars. The barrier prototypes consisted of a slab measured 2.5 × 3.0 m [98.4 × 118.1 in.] with a 225 mm [8.9 in.] thickness and a barrier of 2.6 m [106.1 in.] long. The barrier prototypes were tested under a monotonic increasing load up to failure. The test results revealed that the behavior of the GFRP-reinforced bridge barriers was comparable to that of the steel-reinforced ones.

Fiber reinforced polymer (FRP) reinforcements, with their excellent mechanical and non-corrosive characteristics are being increasingly used as a replacement for conventional steel reinforcement. ACI 440.1R-06 equation for determining the development length of FRP bars is based on Glass FRP (GFRP) bars and may not be applicable for Carbon FRP (CFRP) bars. This paper presents the results of an experimental study on the flexural behavior, bond characteristics, and development length of concrete beams reinforced with CFRP bars. Twelve beams were fabricated and tested. All beams were tested up to failure using a four point bending regime. The results indicated that the average bond strength of CFRP bars in concrete is about 15% higher than those of GFRP bars at comparable concrete strength. The ACI 440.1R-06 over estimated the development length of the CFRP bars by slightly above 30%, while CAN/CSA-S6-06 equation was unconservative by 50%.

This paper presents an experimental study on shear performance of concrete I-beams with fiber reinforced polymers (FRP) as internal reinforcement. A total of four beam tests were conducted, including one test without shear reinforcement and three tests with glass fiber reinforced polymers (GFRP) stirrups. In all specimens, GFRP bars were used as flexural reinforcement. The test variable was the ratio of shear reinforcement. In the test without stirrups, diagonal tension failure occurred. Failure due to rupture of the GFRP stirrups rupture was observed in the test with a shear reinforcement ratio of pw = 0.75% and web crushing failure occurred in the beam tests with pw = 1.26% and pw = 2.26% respectively. The experimentally obtained shear strengths were then compared to calculated design values using equations provided in the modified Eurocode 2, ACI 440.1R06, and CSAS806-2.

This paper investigates the design of fiber reinforced polymer (FRP) reinforced concrete based on ACI 440.1R serviceability requirements related to deflection control of one-way slabs and rectangular beams, and uses this information as the basis for evaluating the minimum member thickness requirements needed to satisfy ACI 318 deflection limits. Serviceability is shown to govern design in most cases, as flexural members designed for deflection control are usually stronger than required. Slabs satisfying deflection requirements have a service load that ranges from 20 to 30% of the nominal member capacity, while service loads for beams range from 35 to 45% of the member capacity. Recommended minimum member thickness values for slabs are too conservative and require revision, while those for beams appear reasonable. A practical approach for design of FRP reinforced concrete members is proposed based on selection of member thicknesses needed to satisfy deflection and strength criteria.