Table 8-1. Parameters used to model behavior of unconfined concrete cylinder in
 compression
 Parameter Value
 Ec (ksi) 4700
 0 (degrees) 20
 t (in.) 0.15
 e (in) 3.6

 10
 -6- Exper. (Aver. of 3)
 8 -X- Model
 8


 4

 2

 0
 0 0.001 0.002 0.003 0.004 0.005
 Strain (in/in)

Figure 8-10. Experimental and calculated stress-strain curves for unconfined control
 cylinders

 The fact that the stress-strain curve of concrete were calculated from the model was

a strong indication that failure mechanisms of concrete can be explained using micro

column buckling theory provided that crack spacing and critical length variation are

known.

 Confined Concrete Model

 For the case of confined concrete the buckling theory suggests that although micro

columns still formed they were braced by the CFRP grid or any other confining material.

The mechanisms of failure are similar in that the micro columns fail by buckling.

 It was assumed that the CFRP grid did not brace the columns immediately but

rather after the micro columns buckled. Once buckled the micro columns pushed against

the CFRP grid which generated a reaction R on the buckled micro columns (see Fig. 8-