The ultimate compressive strength and strain for concrete were
assumed to be 29.1 MPa and 0.38%, respectively. The theoretical
moment-curvature plots for the damaged composite girders before
retrofitting are shown in Fig. 8. It is apparent that cutting the flange reduced the ultimate moment capacity and rigidity of the
sections significantly. The ultimate moment capacity of the com-
posite girder reduced 12, 24, and 48% while the yielding mo-
ments~moments at the onset of tension flange yielding! decreased
by 16, 33, and 67% as a result of 25, 50, and 100% loss of tension
flange area, respectively. Meanwhile, the flexural rigidity of sec-
tions reduced by 14, 29, and 63% before yielding due to losses of
25, 50, and 100%, respectively. Three damaged sections were
then assumed to be retrofitted. CFRP provided additional tension
force to overcome the loss of steel flange. The required area of
composites was selected such that the tensile stress in the CFRP
layers remained between 30 and 35% of their ultimate tensile
strength after the tension flange yielded. One, three, and five lay-
ers of CFRP sheet were considered for repairing the sections with
25, 50, and 100% tension flange loss, respectively. The ultimate
moment capacity and rigidity of the retrofitted sections increased
significantly, as shown in Fig. 9. The ultimate moment capacity of
the girders with 25, 50, and 100% loss improved by 39, 107, and
233%, while the yielding moment increased by 6, 25, and 85%,
respectively. The elastic and postelastic rigidity of the retrofitted sections increased as well. Girders with 25, 50, and 100% loss
showed a 5, 21, and 75% increase in their elastic rigidity, respec-
tively. Rigidity in the plastic region ~the slope of the linear seg-
ment! displayed much higher improvements and increased 6.3,
17.3, and 29.7 times for 25, 50, and 100% loss of tension flange,
respectively. A summary of the theoretical values for the ultimate
capacity and the rigidity of the sections is listed in Table 2.