The first stage was linear up to approximately 18 k-ft moment at which a slight reduction

of slope is noted (see Fig. 5-17) due to cracking. Beyond cracking, both curves were

linear up to 117 kip-ft for specimen 3 and 150 kip-ft for specimen 4. Beyond those points,

however, the stiffness begins to deteriorate due to further cracking. This small reduction

in stiffness was seen in specimen 4 but not in specimen 3 due to specimen failure. It

should be noted that another reduction in the slope of the curve for specimen 4 was

observed at approximately 190 k-ft moment.

















Figure 5-16. Specimen 4 after testing

 The moment capacity of specimen 4 compared to specimen 3 was improved by

58% and the improvement was attributed to the effect of the CFRP grid in both

strengthening the section with its longitudinal strands but more significantly by providing

confinement to concrete.

 It can be argued that the ductility of the section has been improved due to the fact

that the area under the curve for the grid reinforced specimen (specimen 4) is

approximately 2.9 times larger than the area of the specimen with no CFRP grid

(specimen 3).