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Title: Effective Moment of Inertia for Calculating Deflections of Concrete Members Containing Steel Reinforcement and Fiber-Reinforced Polymer Reinforcement

Author(s): Peter H. Bischoff and Andrew Scanlon

Publication: 318Reference



Appears on pages(s): 68-75

Keywords: beam; deflection; reinforcement; slab

Date: 1/1/2007

The effective moment of inertia expression proposed by Branson in 1963 and incorporated into the ACI Code is reevaluated. It is found that Branson’s expression is valid for members with steel reinforcement ratios greater than 1%. This expression, however, overestimates member stiffness at lower reinforcement ratios and gives a member deflection less than expected as demonstrated by comparison with test results. Branson’s approach also underestimates deflection of slender walls with a central layer of reinforcement, as well as deflection of fiber-reinforced polymer (FRP)-reinforced concrete beams. An alternative expression is presented that is shown to be valid for all reinforcement ratios for both steel and FRP reinforcement.


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