11). This generated extra load which was manifested into higher stresses and higher

strains (higher ductility) for the cylinder.

----------------------------------- -----------


 5 -------------- -J-R





----------------------------------- -----------
i ... 3 2 1 0

Figure 8-11. Restraint of micro columns by CFRP grid strand

 Because it was assumed that the micro columns buckle prior to being braced by the

CFRP grid the model in Fig. 8-11 treated the micro columns as axially rigid columns with

real hinges and rigid body motions. It was assumed that only the micro columns adjacent

to the CFRP grid strand were restrained and the entire extra load from confinement was

carried by those micro columns.

 The lateral displacement (5) was determined using geometry (Fig. 8-12) in terms of

the length of the micro column (L) and the axial compressive strain (e). The strain used to

determine the lateral displacement was the strain calculated using Equations 8-8 and 8-

10. Using the Pythagorean Theorem and rearranging the equation the lateral displacement

at a given strain was equal to:

 L 2
 = 2 E, E, (8-11)


 The load (PR) contributed by the restrained micro column was calculated by

summing moments about point B (Fig. 8-12). After rearranging the equation the load PR

was: