Table 1 Criteria according to the limit states.

Fully deteriorated (FRP alone)

Pressure alone

$\frac{{\mathit{\epsilon }}_s·F{S}_s}{{\mathrm{\epsilon }}_{frp}}+\frac{{\mathit{\epsilon }}_l·F{S}_l}{{\mathit{\epsilon }}_{frp}}\le 1.0$

Critical pressure be less then tensile strength of FRP

Combined pressure and external loads

$\frac{{\mathit{\epsilon }}_{comp}·FS}{{\mathit{\epsilon }}_{frp}}\le 1$

Critical strain be less than ultimate tensile strain of FRP

Buckling

$\frac{p_{buck}}{p_{cr}}\le 1$

Critical buckling pressure be less than buckling resistance

Partially deteriorated (inner core & FRP acting together)

Combined pressure and external loads

$\frac{{\mathit{\epsilon }}_{comp}·FS}{{\mathit{\epsilon }}_{frp}}\le 1$

Critical strain be less than ultimate tensile strain of FRP

Concrete crushing

$\frac{{\mathit{\epsilon }}_{comp}·FS}{{\mathit{\epsilon }}_{co}}\le 1$

Critical compressive strain in concrete be less than ultimate compressive strain of concrete

Debond

$\frac{{\mathit{\epsilon }}_{comp}·FS}{{\mathit{\epsilon }}_{deb}}\le 1$

Critical strain in FRP be less than debonding strain

Radial tension

$\frac{{\mathit{\sigma }}_{rt}·FS}{{\mathit{\sigma }}_{rf}}\le 1$

Radial tensile stress between FRP and inner core be less than radial tensile bond strength

Buckling

$\frac{p_{buck}}{p_{cr}}\le 1$

Critical buckling pressure be less than buckling resistance