Rational Procedure for Calculating Deflections of RC Beams Strengthened with FRP


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Title: Rational Procedure for Calculating Deflections of RC Beams Strengthened with FRP

Author(s): H. A. Rasheed, H. Charkas, and H. G. Melhem

Publication: Special Publication

Volume: 210


Appears on pages(s): 115-148

Keywords: deflection; flexural strengthening; FRP plates; reinforced concrete beams; serviceability

Date: 2/1/2003

The use of externally bonded FRP plates has been established as an effective means to strengthen RC beams in flexure and shear. Few investigators have attempted to propose minor modifications to the current ACI empirical equation orginally developed for the effective moment of inertia of unstrengthened RC beams. In contrast, the present work develops a rational procedure for calculating the deflections of beams at any load stage. The procedure assumes a trilinear moment-curvature response characterized by section flexural crack initiation, yielding and ultimate capacity. This model incorporates some tension stiffening effects ans assumes the section to be fully cracked only upon or near steel yielding. A generalized solution is presented for the case of beams having any extent of uncracked, partially-cracked and post yielded regions. The curvature distribution is determined for each region and closed form equations are developed for the cases of 4-point bending and uniform load. Comparisons with experiments indicate the effectiveness of the procedure for properly anchored plates. Parametric studies are conducted to explore the applicability of the ACI original and modified equations for a wide range of geometric and material properties. As a result, improved ACI equations are suggested for use in practical deflection calculations.