This paper deals with the flexural strengthening of reinforced concret
e beams by means of composite thin plates. It presents a theoretical m
odel which was developed to study the effects of various parameters on
the flexural behavior of strengthened beams. From a parametric study
carried out with the model, it was found that the most significant par
ameters affecting the ultimate flexural resistance are the concrete co
mpressive strength, the percentage of reinforcing steel, the modulus o
f elasticity of the composite material and the thickness of the streng
thening plate. To avoid brittle flexural failure of strengthened beams
, limiting quantities of strengthening material are specified as a fun
ction of a strengthening index.