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Numerical Analysis of Thermal Behavior of Concrete Cover Around FRP-Bars in Cold Region

Abstract

The coefficient of thermal expansion of fiber reinforced polymer (FRP) in transverse direction is 3–8 times greater than that of hardened concrete. This thermal incompatibility between FRP bar and concrete in transverse direction may cause circumferential cracks within concrete at FRP bar/concrete interface under low temperatures and eventually the debonding of FRP bar from concrete. This paper presents numerical analysis using ADINA finite element software to investigate the thermal behavior of concrete cylinders reinforced with glass FRP bar (GFRP) in cold regions. The non-linear numerical results show that the first circumferential cracks occur within concrete at FRP bar/concrete interface at thermal loads ΔT cr varied between −35 and −25°C for GFRP bar-reinforced concrete cylinders having a ratio of concrete cover thickness to FRP bar diameter (c/d b) varied from 0.8 to 3.6 and a concrete tensile strength of 4.1 MPa. The numerical radial tensile stresses in concrete at the interface compared with those predicted from the analytical model are similar until the appearance of the circumferential cracks in concrete whose analytical results are greater. The ratio c/d b has no significant effect on the transverse thermal strains at FRP bar/concrete interface and also at external surface of concrete cover for a ratio of c/d b ≥ 1.5. Also, the transverse thermal strains, at external surface of concrete cover, predicted from non-linear numerical model are in good agreement with those obtained from the linear analytical model and experimental tests.

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Abbreviations

a :

Radius of FRP bar

b :

Radius of concrete cylinder

c :

Concrete cover thickness

d b :

Bar diameter

CTE:

Coefficient of thermal expansion

E c :

Modulus of elasticity of concrete

E l :

Longitudinal modulus of elasticity of FRP bar

E t :

Transverse modulus of elasticity of FRP bar

\({f^{\prime}_{{\rm c}28}}\) :

Compressive strength of concrete

f ct28:

Tensile strength of concrete

f fu :

Ultimate tensile strength of FRP bar

P :

Radial pressure exerted by surrounding concrete on FRP bar

r :

Ratio of radius of cylinder to that of FRP bar rb/a

α c :

Coefficient of thermal expansion of concrete

α l :

Longitudinal coefficient of thermal expansion of FRP bar

α t :

Transverse coefficient of thermal expansion of FRP bar

ΔT :

Temperature variation (thermal load)

ΔT cr :

Thermal load producing the first circumferential cracks in concrete at FRP bar/concrete interface

\({\varepsilon_{{\rm ct}}}\) :

Circumferential strains in concrete

\({\varepsilon_{{\rm ft}}}\) :

Circumferential strains in FRP bar

ν c :

Poisson’s ratio of concrete

ν tt :

Transverse Poisson’s ratio of FRP bar

ν lt :

Longitudinal Poisson’s ratio of FRP bar

σ ρ :

Radial tensile stress

σ t :

Circumferential compressive stress

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Correspondence to Ali Zaidi.

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Zaidi, A., Masmoudi, R. Numerical Analysis of Thermal Behavior of Concrete Cover Around FRP-Bars in Cold Region. Arab J Sci Eng 37, 489–504 (2012). https://doi.org/10.1007/s13369-012-0173-x

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Keywords

  • Bars
  • Concrete cover
  • Fiber reinforced polymers
  • Low temperatures
  • Thermal stresses
  • Thermal strains