the control cylinders. Specimens Grid 4, 5 and 6 had approximately 25% more area under

the stress-strain curve than specimens Grid 1, 2 and 3.


2

0
0.


000


0.004


 0.008
Axial Strain (in/in)


0.012


0.016


Figure 3-13. Stress-strain curves for typical control and grid cylinders

Table 3-4. Area under stress-strain curve
Type Area Aver. area
 (ksi in/in) (ksi in/in)
 Control 1 0.0169
 Control 2 0.0157 0.015
 Control 3 0.0124
 Grid 1 0.0341
 Grid 2 0.0368 0.0338
 Grid 3 0.0304
 Grid 4 0.0395
 Grid 5 0.0412 0.0421
 Grid 6 0.0456

 All grid cylinders reached a peak axial load followed by a descending post peak

curve. Other researchers observed such a behavior in lightly confined concrete. Harries

and Kharel (2003) made similar observations for their one and two-ply E-Glass confined

cylinders. Sfer et al. (2002) studied the behavior of concrete under triaxial compression

and their axial stress-strain curves at low confining pressures had a descending post peak

curve. The increase in the concrete strength was between 10% and 20%, which compares

to the 11% increase observed for our cylinders. In the case of the CFRP grid confined


-8- Control 2
-A- Grid 3
8- Grid 5