The complete moment-curvature diagram is calculated by applying increasingly

larger levels of section curvature to the cross-section using a moment curvature algorithm

to find the location of the neutral axis by iteration.

 For the case of the tube beam a concrete confinement model was integrated into the

M-D program. However, the M-D program is not configured to assign different material

properties for confined or unconfined concrete but rather assigns the same properties

throughout the section. Therefore when used to produce the M-0 curve of the tube beam

confined concrete properties were used for the entire section. However, the top cover

layer was removed and the section was analyzed as a section with a depth of 17 in. rather

than the actual 18 in. This solution is a lower bound solution for the strength evaluation

of the CFRP grid tube beam. From hereon the results from the moment curvature

program will be referred to as theoretical results.

 The M-0 curves for both beams were also calculated based on the fiber model

described in a previous section in this chapter.

 The experimental, theoretical and fiber model M-0 diagrams were calculated for

both beams. The theoretical and fiber model M-D diagrams for the control beam (see Fig.

4-23) were the same. However, the theoretical peak load is approximately 5% lower that

the peak load calculated using the fiber model. This difference was attributed to the

different models used to represent the stress-strain behavior of concrete between the two

models. The stiffness of the mid-span location was lower that the theoretical fiber model

stiffness. The stiffness of the south load location was comparable to the stiffness of the

diagrams calculated theoretically and using the fiber model.