Many structures, such as bridges and parking garages, are usually treated with deicing salts and are, therefore, subjected to an aggressive environment. For such structures, possible corrosion of reinforcing and prestressing steel may eventually lead to concrete deterioration and loss of serviceability or capacity. To control corrosion problems, professionals have turned to alternative reinforcements such as epoxy-coated steel bars. However, such remedies were only found to slow down, rather than eliminate corrosion problems. Recently, fiber reinforced polymer (FRP) materials have emerged as an alternative to steel reinforcement. FRP materials are corrosion resistance and exhibit several properties that make them suitable as structural reinforcement (ACI Committee 440, 1996 and Japan Society of Civil Engineers (JSCE), 1997). In order to apply this new technology to practice, a better understanding of the behavior of FRP reinforced members is required. In addition, current codes provide no guidance on how to modify the existing requirements when reinforcing with materials other than steel.

Some of the main differences of FRP reinforcement when compared to steel reinforcement are higher tensile strength, lower stiffness, and elastic behavior up to failure with no yielding (no plasticity). These differences are reflected on the flexural behavior of FRP-reinforced members. The conventional concept of under-reinforced members as a favorable design approach is not practical for FRP-reinforced members because it will result in members having lower stiffness hence, larger deflection and crack widths are expected.

Available experimental results of FRP reinforced sections indicate that when FRP reinforcing bars ruptured (tension-controlled failure), the failure was sudden and led to the collapse of the member (Nanni, 1993; GangaRao and Vijay, 1997; and Theriault and Benmokrane, 1998). However, a more progressive and less catastrophic failure was observed when the member failed due to the crushing of concrete (compression-controlled failure). This behavior results in higher deformability, which is defined as the ratio of energy absorption (area under moment-curvature curve) at ultimate to that at service level (Jaeger et al., 1997).

In general, flexural design can be performed using the principles of the ultimate strength method given in ACI 318-95, building code or according to the principles of the allowable stress method using the approach provided in Appendix A of the ACI 318-95, building code. The latter can produce more conservative results (e.g. stiffer sections having smaller deflections). To address the effect of FRP properties on the flexural behavior, comparisons will be made for sections reinforced with the three main types of FRP reinforcement namely, glass (GFRP), aramid (AFRP), and carbon (CFRP). The properties of the three types considered hereafter are given in Table 1. These are typical properties of FRP bars available in the market today.