Flexural members - Reinforced Concrete with FRP Bars: Mechanics and Design - page 142

4.11 TEMPERATURE AND SHRINKAGE
REINFORCEMENT

No experimental data are available in the technical literature to establish
the minimum FRP reinforcement ratio for shrinkage and temperature, ρ f,ts .
Accordingly, the following equation adopted from ACI 318-11 is proposed
by ACI 440.1R-06:

0.0018 60,000

E
E

ρ=

s
f

(4.119)

fts ,

f

fu

0.0018 414

E
E

s

[or ρ= in SI units]

fts ,

f

fu f

where E s is the modulus of elasticity of steel. An upper bound equal to
0.0036 and a lower bound equal to 0.0014 are also set for ρ f,ts . The spacing
of the shrinkage and temperature reinforcement should not exceed three
times the slab thickness, or 12 in., whichever is smaller.

4.12 SAFETY FIRE CHECKS FOR BENDING
MOMENT CAPACITY

A recent publication by Nigro et al. [41] proposes a new methodology to
perform fire safety checks for bending moment capacity of unprotected
FRP RC flexural members exposed to fire on the side of the FRP bars
under tension. The objective of this approach is to compute the bend-
ing moment capacity of the member taking into account the reduced
FRP bar properties due to the exposure to high temperatures and the
available anchorage developable in the zones not directly exposed to
the fire.
Nigro et al. propose the following equations to estimate the “average”
deterioration factors for tensile strength and modulus of elasticity of CFRP
and GFRP bars at a specific temperature T expressed in degree Celsius as
shown in equations (4.120) and (4.121) [1°C = 5(1°F−32)/9].

()

fT
f

0.05 f

ρ= () T = forGFRPbars

f

− 11 3.55

0.05 +⋅ 8.010 ⋅ T

fu

(4.120)

()

fT
f

0.06

f

ρ= () T = forCFRPbars

f

− 10 3.33

0.06 +⋅ 2.010 ⋅ T

fu