Rationale for the ACI 440.1R-06 Indirect Deflection Control Design Provisions

Synopsis: Compared to ordinary steel reinforcement, Fiber-Reinforced Polymer (FRP) reinforcing bars have a lower stiffness, display a brittle-elastic response, and possess particular bond characteristics. The dependence on these distinctive features makes deflection control in FRP-reinforced concrete beams and one-way slabs a more elaborate process compared to the traditional serviceability design of steel-reinforced members. This paper reports the rationale and fundamental concepts backing the indirect deflection control procedure for concrete beams and one-way slabs reinforced with FRP bars adopted by ACI 440.1R-06. The fundamental procedure can be applied regardless of the type of reinforcement; it is independent of the member’s stiffness through the cracked stage; and it is expressed as a function of the deflection-span ratio, which allows designers to fully control deflections depending on applicable serviceability limits. The paper also explains the simplifications made to the fundamental procedure that led to the development of the indirect deflection control procedure in tabular form found in ACI 440.1R-06, including the method by which tension stiffening effects are accounted for.