where ni was the number of CFRP grid layers, ngs was the number of grid strands, bg was
the width of the grid strands, tg was the thickness of the grid strands and h was the height
of the cylinder.
The secant modulus of elasticity of concrete (Ec) was calculated based on existing
empirical expressions (Nawy 2003):
E = 57.f7 (3-2)
wheref'c was the minimum specified compressive strength of concrete, in psi, at 28 days
and Ec is in ksi.
To determine the confinement strength (fr) simple pressure vessel mechanics were
used (see Fig. 3-14). The equilibrium condition required the force from the confining
strength be equal to the force in the FRP encasement.
Carbon grid
fgu teg fgu teg
Figure 3-14. Cylindrical pressure vessel
The equilibrium condition for the confined cylinder was expressed as follows:
f,, dg = 2 teg fgu (3-3)