Behavior of FRP Bars-Reinforced Concrete Slabs under Temperature and Sustained Load Effects
2. Experimental Section
2.1. Description and Instrumentation of Slabs
|Slabs||Concrete cover, c (mm)||Bar diameter db (mm)||c/db||Longitudinal modulus of elasticity, EC (GPa)||Compression strength (MPa)||Tensile strength (MPa)|
|SA195.25.16||25||15.9||1.57||26.17 ± 0.4||33.83 ± 1||1.94 ± 0.04|
|SA200.30.16||30||15.9||1.88||24.80 ± 0.8||30.39 ± 2||2.58 ± 0.04|
|SA215.45.16||45||15.9||2.83||26.17 ± 0.4||33.83 ± 1||1.94 ± 0.04|
|SA195.25.19||25||19.1||1.31||26.53 ± 0.3||34.77 ± 0.7||2.77 ± 0.15|
|SA200.30.19||30||19.1||1.58||27.34 ± 0.7||36.93 ± 2||2.92 ± 0.25|
|SA215.45.19||45||19.1||2.36||27.34 ± 0.7||36.93 ± 2||2.92 ± 0.25|
2.2. Test Procedure
|Bars diameter db (mm)||15.9||19.1|
|Longitudinal Modulus of elasticity, Efl (GPa)||47.0 ± 0.3||52.2 ± 1.2|
|Transverse modulus of elasticity, Eft (GPa)||7.75||7.87|
|Poisson’s ratio in the longitudinal direction, νlt||0.28 ± 0.005||0.28 ± 0.008|
|Poisson's ratio in the transverse direction, νtt||0.38||0.38|
|Ultimate tensile strength (MPa)||700 ± 24||691 ± 7|
|Guarantee tensile strength (MPa)||683||656|
|Ultimate tensile strain (%)||1.50 ± 0.06||1.33 ± 0.03|
|TCTE* (αft) [×10−6 ]/°C||27.35 ± 0.35||22.45 ± 0.31|
|LCTE‡ (αfl) [×10−6]/°C||6.81 ± 0.9||6.61 ± 0.1|
2.4. Results and Discussion
2.4.1. Thermo-Mechanical Behavior of FRP Bars
2.4.2. Thermo-Mechanical Behavior of Concrete
3. Analytical Model
- A perfect bond between concrete and FRP bar.
- The behavior of concrete and FRP bars is linear elastic.
- The cross section of the concrete cylinder remains plane after deformation.
- Absence of transverse reinforcing bars to evaluate only the contribution of the concrete cover to support the tensile stresses due to applied loads.
4. Comparison of Analytical and Experimental Results
- The mechanical load effect of 20% of the ultimate load (Fu) of reinforced concrete slabs has no significant effect on the transverse thermal strains of GFRP bars embedded in concrete under temperature variation from −30°C to +60°C.
- At high temperature (>40°C), longitudinal thermal strains at the GFRP bar/concrete interface have been reduced under applied mechanical loads. This reduction reached 30%, for a temperature of +60°C, due to the decrease of radial pressure generated at the interface. However, for temperatures variation from −30°C to +40°C, the mechanical load has no big influence on longitudinal thermal strains at the GFRP bar/concrete interface.
- The thermo-mechanical behavior of GFRP bars embedded in concrete of actual slabs is linear elastic.
- The concrete cover thickness variation has no big effect on transverse thermal strains at GFRP bar/concrete interface, for temperature variation from −30 °C to +60 °C. However, the transverse thermal strains decrease with the increase of FRP bar diameter.
- At high temperature, transverse tensile concrete strains at external surface of concrete cover were reduced under mechanical load. This reduction varied from 5% to 15%, for a temperature of +60 °C, due to the decrease of the radial pressure and consequently the reduction of radial crack propagations through concrete cover. While, for the low temperature (−30 °C), the mechanical load of 20% Fu, has no remarkable effect on transverse tensile concrete strains.
- Ratiosof concrete cover thickness to FRP bar diameter (c/db) varied from 1.3 to 2.8 are sufficient to avoid failure of the concrete cover of GFRP bars—reinforced concrete slabs under combined thermal and mechanical service loads for materials used in this study.
- The transverse strains, at FRP bar/concrete interface of concrete slab under thermal and mechanical loads, predicted from the analytical model are greater than those obtained from experimental tests. This is due to the presence of cracks produced within concrete at the interface which is not considered in the linear analytical model based on the theory of elasticity.
- The transverse strains, at FRP bar/concrete interface, predicted from the proposed model, are in good agreement with experimental results obtained from GFRP bars-reinforced concrete slabs under the combined thermal load (from −30 °C to +60 °C) and mechanical load (20% of the ultimate load of slabs).
Concrete cover thickness
FRP bar diameter
Modulus of elasticity of concrete
Modulus of elasticity of FRP bar in the transverse direction
Compressive concrete strength
|r = b/a|
ratio of concrete cylinder radius “b” to FRP bar radius “a”
Transverse coefficient of thermal expansion of FRP bars
Coefficient of thermal expansion of concrete
Circumferential strains in FRP bar at the interface of FRP bar/concrete
Circumferential strains in concrete at the interface of FRP bar/concrete
Longitudinal strain in the FRP bar due only to the mechanical loading
Longitudinal strain in the tensile concrete due only to the mechanical loading
Poisson’s ratio of concrete
Poisson’s ratio of FRP bar in the transverse direction
Poisson’s ratio of FRP bar (force applied in longitudinal direction and strains measured in transverse direction)
Radius from the center of the concrete cylinder
Radial stress in concrete cover
Circumferential stress in concrete cover
Maximum circumferential stress in concrete cover
Conflicts of Interest
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