Implementation of GFRP-RC Code Provisions: Detailing for Deflection Criteria

The American Concrete Institute has developed a design standard for glass fiber-reinforced polymer (GFRP) RC members, dependent to their standard for steel-reinforced structural concrete. Design examples conforming to code language have been developed and their solutions examined to understand the impacts that code requirements have on the design of GFRP-RC members. The impacts include selecting member dimensions and reinforcement on the basis of serviceability requirements, rather than strength, and the related detailing issues involving bar cutoff points. As the design of GFRP-RC members is typically controlled by serviceability requirements, some reinforcement may be provided to satisfy deflection requirements. Cutoff points for such bars must be located differently than for steel bars, where the cutoff point is determined by strength requirements. A proposed method locates cutoffs by calculating the resulting maximum deflections as the cutoff point is varied. A second, approximate, approach locates cutoffs at points where continuing bars provide the same value for effective moment of inertia as that available from all bars at the critical section. The second method results in longer bar lengths but is more easily applied. Shear and crack control requirements should also be checked at cutoff locations.