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


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

Author(s): C.E. Ospina and S.P. Gross

Publication: Special Publication

Volume: 230


Appears on pages(s): 651-670

Keywords: deflection; FRP-reinforced members; indirect deflectioncontrol; one-way slabs; serviceability design; tension stiffening

Date: 10/1/2005

Compared to ordinary steel reinforcement, Fiber-Reinforced Polymer (FRP)reinforcing bars have a lower stiffness, display a brittle-elastic response, and possessparticular bond characteristics. The dependence on these distinctive features makesdeflection control in FRP-reinforced concrete beams and one-way slabs a moreelaborate process compared to the traditional serviceability design of steel-reinforcedmembers. This paper reports the rationale and fundamental concepts backing theindirect deflection control procedure for concrete beams and one-way slabs reinforcedwith FRP bars adopted by ACI 440.1R-06. The fundamental procedure can be appliedregardless of the type of reinforcement; it is independent of the member’s stiffnessthrough the cracked stage; and it is expressed as a function of the deflection-spanratio, which allows designers to fully control deflections depending on applicableserviceability limits. The paper also explains the simplifications made to thefundamental procedure that led to the development of the indirect deflection controlprocedure in tabular form found in ACI 440.1R-06, including the method by whichtension stiffening effects are accounted for.