Abstract
It is technologically possible to strengthen steel reinforced concrete structures by bonding externally carbon epoxy sheets. Few results exist on the mechanical behavior of strengthened structures subjected to service loads. Consequently, large safety factors are taken into account, most of all concerning the limitation of steel stresses. In order to provide a more accurate characterization of their serviceability, beams are investigated by utilizing a full-field optical measurement technique. The results lead to an original analysis of cracks growth and opening in unstrengthened and strengthened beams.
Résumé
Il est technologiquement possible de renforcer des ouvrages en béton armé présentant des comportements pethologiques préoccupants en stratifiant les faces extérieures de l'ouvrage avec des matériaux composites carbone-époxy. Le manque de connaissance sur le comportement en service des ouvrages renforcés nécessite la prise en compte d'importants coefficients de sécurité notamment sur la contrainte admissible des aciers. Dans l'objectif d'étudier le comportement de poutres renforcées et sollicitées sous charge de service. l'application d'une technique d'extensométrie optique au cas du béton armé est réalisée. Dans cette étude, l'état de fissuration de poutres renforcées ou non renforcées est particulièrement étudié.
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Abbreviations
- A's:
-
total area of compression rebar section (mm2)
- As:
-
total tension steel section (mm2)
- Af :
-
total area of carbon fiber section at the bottom of the beam (mm2)
- A,B:
-
coefficient
- b:
-
beam width (mm)
- d:
-
effective height of member section (mm)
- I(x,y) :
-
light intensity reflected
- I 0 :
-
local intensity bias
- I:
-
sectional moment of inertia (mm4)
- frgn :
-
2π-periodic continuous function
- f x :
-
spatial frequency of the grid lines
- k 1,k2 :
-
coefficients taking into account steel friction and stress (0.8 and 0.5)
- M:
-
moment (N.mm)
- N :
-
equivalent young modulus ratio (Steel versus concrete, Es/Ee)
- n f :
-
equivalent young modulus ratio (composite versus concrete, Ef/Ec)
- (x,y) :
-
position of pointM in the Cartesian reference frame
- R 0 :
-
local rotation at the origin
- S rm :
-
average crack spacing for the final load (80 mm in our case)
- U x(x,y) :
-
x component of the displacement field over the lateral surface of the beam
- U 0 :
-
horizontal displacement at the origin:U 0=Ux(0,0)
- Wk :
-
crack width (mm)
- Z:
-
distance from the bottom of the beam to the neutral axis (mm)
- α:
-
coefficient
- β,β1,β2 :
-
design coefficient
- ε m :
-
mean strain taking into account tension stiffening and shrinkage effects
- ε m0 :
-
residual strain when structure unloaded
- φ\(\left( {\vec R} \right)\) :
-
phase of the function frgn
- φ:
-
bar size (mm)
- φ:
-
contrast
- σ s :
-
stress in steel rebars, calculated on the basis of the current cracked section (MPa)
- σ sr :
-
the stress in steel rebars, calculated for a cracked section with loading conditions corresponding to the first crack occurrence (MPa)
- σ s,f :
-
steel stress with external bonded FRP
- ρ r :
-
effective reinforcement ratio
- χ:
-
average curvature
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Editorial Note Prof. Patrice Hamelin is a RILEM Senior Member.
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Ferrier, E., Avril, S., Hamelin, P. et al. Mechanical behavior of RC beams reinforced by externally bonded CFRP sheets. Mat. Struct. 36, 522–529 (2003). https://doi.org/10.1007/BF02480829
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DOI: https://doi.org/10.1007/BF02480829