The concrete inside the CFRP grid tubes maintained the circular shape of the tube

even after the tube failed and confinement was lost (Fig. 4-13). The CFRP grid ruptured

at a particular location and not throughout the constant moment region which was why

the concrete maintained that shape.





















Figure 4-13. Tube beam compression zone after testing

 Fiber Model Analysis

 The peak loads for both beams were calculated using a fiber model analysis of the

beam cross-section. The compression zone of the tube beam was separated into two

regions with regard to concrete properties. The first region was the concrete cover on top

of the CFRP grid tubes and the second region was from the neutral axis to the top of the

CFRP grid tubes (see Fig. 4-14). The first region was extended approximately 0.25 in.

below the top of the CFRP grid tubes to account for the unconfined concrete at the sides

and between the grid tubes. The first region was assigned unconfined concrete properties

and the second region confined properties. The concrete area from the neutral axis to the