Deflection Calculation Using an Effective Moment Inertia for FRC


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Title: Deflection Calculation Using an Effective Moment Inertia for FRC

Author(s): P.H. Bischoff

Publication: Special Publication

Volume: 248


Appears on pages(s): 17-30

Keywords: deflection; effective moment of inertia; fiber-reinforced concrete; reinforced concrete beams; stiffness; tension stiffening

Date: 9/1/2007

Fiber-reinforced concrete (FRC) has a post-cracking (residual) tensile strength which can provide extra stiffness to a reinforced concrete structure. This helps to reduce deflections and control cracking. Basic concepts of tension stiffening and the tensile capacity of the FRC at a crack are used to develop a rational model for both axial and flexural member stiffness. Axial member stiffness is defined by an effective concrete area and validated with experimental results. An effective moment of inertia is used to define the flexural stiffness, and the computed response of a plain reinforced concrete beam is compared with an FRC reinforced concrete beam. FRC is shown to increase member stiffness by between 10 to 50% depending on the amount and type of conventional reinforcement and post-cracking strength of the FRC used. The expressions developed for member stiffness are compatible with the ACI 318 approach of using an effective moment of inertia and can be easily incorporated into existing design procedures to ensure that deflection requirements are satisfied.