Flexural design methodology for concrete beams reinforced with fiber-reinforced polymers

The use of fiber-reinforced polymer (FRP) as structural reinforcement for concrete beams requires a flexural design methodology that provides adequate safety from brittle failure. Recognizing the absence of inelastic material behavior it is proposed that safety for FRP-reinforced flexural members should be evaluated based on total material strain energy density (SED) at the critical cracked section. Safety is then defined as the ratio of SED at ultimate relative to service. A proposed minimum energy factor of safety (EFS) of 25 is derived from a companion analysis of under-reinforced steel beams within current code-mandated design limitations. The energy criteria conclude that the minimum EFS for FRP-reinforced members is only achievable provided the service stress in the concrete is restricted to 0.35f(c)'. The result is low working stresses in the FRP reinforcement and a high degree of reserve strength. High-strength concrete is recommended to make more efficient use of the FRP tensile strength.