The Story Behind Proposed Changes to ACI 440 Deflection Requirements for FRP-Reinforced Concrete


  • The International Concrete Abstracts Portal is an ACI led collaboration with leading technical organizations from within the international concrete industry and offers the most comprehensive collection of published concrete abstracts.

International Concrete Abstracts Portal


Title: The Story Behind Proposed Changes to ACI 440 Deflection Requirements for FRP-Reinforced Concrete

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

Publication: Special Publication

Volume: 264


Appears on pages(s): 53-76

Keywords: deflection; effective moment of inertia; fiber-reinforced polymer (FRP); reinforced concrete; serviceability; stiffness.

Date: 10/1/2009

Serviceability related to deflections and cracking often controls design of fiber reinforced polymer (FRP) reinforced concrete. The existing approach prescribed in ACI 318 for computing deflection of steel reinforced concrete overestimates member stiffness when FRP is used as the reinforcement. Deflection is then underestimated. Numerous proposals have consequently been made for computing deflection of FRP reinforced concrete, and have mostly involved modifications to Branson’s original ACI expression for the effective moment of inertia Ie. This paper reviews the different procedures used in the past by ACI Committee 440 to compute deflection of FRP reinforced concrete members, and discusses deficiencies of past and present ACI 440.1R deflection calculation guidelines. A case is made for the need to adopt a more rational approach to compute deflection and the basis for proposed changes are reviewed and explained in detail. A statistical comparison of past, present, and proposed approaches for computing deflection are compared with an experimental database that justifies the need for a more rational approach to computing deflection. The paper ends with a clear set of deflection procedures for carrying out serviceability design of FRP reinforced concrete.