Constituent Materials and Properties - Strengthening Design of Reinforced Concrete with FRP - page 67

x

+θ

-θ

y

FIGURE 3.11 Typical angle ply laminate with fiber orientations with respect to the loading

axes.

Along the angle-ply laminate:
Combining the CTEs of the two identical plies together,

( ) ( )

2 2 2 2 2 2

α= α+α+α+α α+α 0.5 CS 0.5 CS CS

x 1 2 1 2 1 2

( ) ( )

α= α+α+α+α α+α 0.5 S

2

C

2

0.5 S

2

C S

2 2

C

2

(3.24)

y 1 2 1 2 1 2

α =α−α +α+α=

( ) ( )

xy

0.5 CS CS 0.5 CS CS 0

1 2 1 2

2

3.11 PROPERTIES OF FRP COMPOSITES (HIGH TEMPERATURE)
The glass transition temperature, T g , is the threshold beyond which the polymer soft-
ens and loses its ability to transfer stress from concrete to fiber. Typical T g values
for resins cured at room temperature range between 140°F-180°F (60°C-82°C). In
bond-critical applications, reaching T g would be the cutoff point for the FRP stress-
carrying capacity. In contact-critical applications, reduced stress along the fiber may
be carried up to 1800°F (1000°C) for CFRP, 350°F (175°C) for AFRP, and 530°F
(275°C) for GFRP (ACI 440.2R-08). Reduction in the tensile strength of CFRP
exceeds 20% at 500°F (260°C), according to Hawileh et al. (2009).

3.12 PROPERTIES OF FRP COMPOSITES (LONG-TERM EFFECTS)
With FRP composites, long-term effects primarily include creep rupture and fatigue.
Creep rupture is a sudden failure at a sustained tensile loading for an extended period
of time. The time-to-failure period is reduced when the sustained tensile stress to
short-term ultimate strength ratio is increased and when the environmental exposure
is increased (ACI 440.2R-08).
Two studies on FRP bars concluded that maintaining the sustained stress ratio
below 0.3 for GFRP, 0.5 for AFRP, and 0.9 for CFRP results in time-to-failure