The authors are grateful to Fundação para a Ciência e Tecnologia for partial financing of thework under Project PTDC/ECM/100538/2008. The authors would like to thank for the helpof Prof. Vladimir Cervenka and Ing. Dobromil Pryl, with ATENA.publishersversionpublishe

Biscaia, Hugo

Chastre, Carlos

Silva, Manuel Américo Gonçalves da

English

New University of Lisbon's Repository

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Degradation of GFRP‐plates bonded to concrete: An experimental approach
based on Mohr‐Coulomb failure criterion
Data · June 2011
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Degradation of GFRP‐plates bonded to concrete: An 
experimental approach based on Mohr‐Coulomb
failure criterion
Hugo Biscaia, Manuel Gonçalves da Silva & Carlos Chastre
Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Portugal
Objectives of the study
1. Characterize the glass FRP/concrete interface by double shear tests;
2. Analyse the degradation imposed to the GFRP/concrete interface by humidity salted 
environments;
3. The lack of information about the modelling of the interface between FRPs and 
concrete is a very actual theme and this work is a contribution to mitigate this gap. 
However, at this point of the study only reference specimens were modulated, i.e., 
without ageing.
4. Make proposals in order to adjust some rules or national codes.
An experimental programme was conducted in order to:
Accelerated ageing tests
0 1 2 3 4 5 6 7
0,0
0,5
1,0
1,5
Dry
No. of days
 Wet/Dry cycles
Wet
Wet and dry cycles  with 5% of salt
0 50 100 150 200 250 300 350 400 450
0
10
20
30
40
50
 
 Temperature
 Relative Humidity
Time (days)
T
e
m
p
e
r
a
t
u
r
e
 
(
º
C
)
0
20
40
60
80
100
Relative H
um
idity (%
)
Accelerated ageing tests
Salt fog cycles (5% of salt)
0 4 8 12 16 20 24
0
1
Dry
No. of hours
 Salt fog cycles
Fog
Fog
Dry
No. of hours
Surface treatmentDry sand blasting with 4 bar of 
pressure.
Proposed shear tests
Characterization of materials
0,0 0,2 0,4 0,6 0,8 1,0
0
5
10
15
20
25
 fc,cub (MPa)

c
 (%)
28 Days
Concrete  
strength
0 1 2 3
0
100
200
300
400
500
600
 f
f
 (MPa)

f
 (%)
Tensile strength 
of the GFRP flat 
coupons
fcm,cub
(MPa)
fcm
(MPa)
fctm (*)
(MPa)
c1 (*) 
(%)
fctm,sp (*) 
(MPa)
Ecm(*)
(GPa)
18.6 16.9 1.65 0.17 1.83 23.18
Concrete  properties:
Flat
coupons
εf m
(%)
ffm
(MPa)
Ef m (MPa)
Reference 2.20 513.9 23.49
GFRP  properties:
(*) According to EC2.
Experimental tests
Specimen
Fmax (kN) δmax (mm)
Média Média
MC‐REF80‐01 17.86
16.06
2.60
2.20MC‐REF80‐02 16.28 2.10
MC‐REF80‐02a 14.03 1.91
MC‐REF20‐01 4.38(*)
4.96
4.37
2.95
MC‐REF20‐02 5.55(**) 6.00
MC‐REF80‐03 25.73 25.73 2.25 3.14
MC‐REF80‐04 34.56
40.34
3.65
5.18
MC‐REF80‐04a 46.12 3.14
(*) Fmax = 17.51kN multiplying by 4 (GFRP with 1/4 of the wide of
other specimens).
(**) Fmax = 22.19kN multiplying by 4 (GFRP with 1/4 of the wide
of other specimens).
0 1 2 3 4 5 6 7 8
0
20
40
60
80
100

L
 = 1.0MPa

L
 = 0.MPa
T
o
t
a
l
 
F
o
r
c
e
 
(
k
N
)
Displacement (mm)

L
 = 0MPa
Reference specimens (at 0h of exposure)
.5MPa
Preliminary considerations
Calculating maximum bond stress…
From equilibrium and compatibility 
conditions of a finite element of FRP with 
length dx, it is obtained:
Assumptions:
i) εf = ds/dx, and εf is the FRP strain;
ii) linear and elastic behaviour is assumed for GFRP;
iii) bond is associated only with shear stresses, i.e., the normal stresses, σn, shown in 
figure above are considered of no influence.
  02
2
 ff tE
s
dx
sd 
where s is the slip between FRP and 
concrete, τ(s) is the local bond stress, x is 
the coordinate axis along the bonded 
length, Ef and tf, respectively, the Young 
modulus and the thickness of the FRP.
Preliminary considerations
Calculating maximum bond stress…
 
max
sel smax
B
o
n
d
 
s
t
r
e
s
s
,
 

Slip, s
 a) Linear law
 b) Bi-linear law
max
max
s
ku

el
u ss
k  max
maxʹ

ff AE
F
dx
ds

0
dx
ds
Assuming, for instance, the ascending branch 
of the bilinear bond‐slip law and introducing 
the boundary conditions of the problem:
where Af is the transversal area of the GFRP 
and Leff is the effective bond length, the 
solution is given by:
at x = 0
at x = Leff
    eff efffff L
Lx‐
tbE
Fxs 
 

 sinh
cosh
    eff efff L
Lx
b
Fx 
 

sinh
cosh   

  

2
coth
2
0
avg
max x
eff
b
L
Land
Preliminary considerations
Calculating maximum bond stress…
0 1 2 3 4 5
0
1
2
3
4
5
6
7
8
 Eq. 18
 
=
  m
a
x
/
 av
g
 = lb/leff
eff
b
L
L
  

  

2
coth
2
0
avg
max x
ctm
ff
eff fc
tE
L 

2
Equation proposed by fib Bulletin 14 where c2 = 2.0 in the case of CFRP. 
In the case of GFRP, previous work, led to c2 = 0.8.
Preliminary considerations
Comparing the maximum bond stress expected with some experimental works…
0 2 4 6 8 10
0
2
4
6
8
10
+4
0%
+2
0%
‐40%
‐20
%
GFRP
 
 m a
x
(
a
)
 
(
M
P
a
)

max
 previsto (MPa)
 Biscaia [23]  Aiello e Leone [96]  Mukhopadhyaya et al. [98]
 Lucas [144]  Projecto PTDC/ECM/100538/2011 [182]
expec ed (MPa)
Experimental results
Reference
specimens
Lateral 
compression 
stress,     (MPa) 
τmed (MPa) τmax (MPa)
MC‐REF80‐01 0.0 0.691 1.296 1.52 1.97
MC‐REF80‐02 0.0 0.682 1.288 1.40 1.81
MC‐REF80‐02a 0.0 0.682 1.288 1.21 1.56
MC‐REF20‐01 0.0 0.706 1.309 1.46 1.91
MC‐REF20‐02 0.0 0.706 1.309 1.85 2.42
MC‐REF80‐03 0.5 0.687 1.292 2.20 2.85
MC‐REF80‐04 1.0 0.699 1.303 2.91 3.79
MC‐REF80‐04a 1.0 0.689 1.294 3.94 5.09
eff
b
L
L
avg
 max
L
1.78MPa
2.85MPa
4.44MPa
MPa0.0
max5.2 
MPa0.0
max6.1 
0 2000 4000 6000 8000 10000
0
10
20
30
40
50

L
=1,0MPa

L
=0,5MPa
 
F
o
r
ç
a
s
 
n
a
 
r
u
p
t
u
r
a
 
p
o
r
 
i
n
t
e
r
f
a
c
e
 
(
k
N
)
Nº de horas de envelhecimento

L
=0,0MPa
Ciclos de nevoeiro salino
0 2000 4000 6000 8000 10000
0
10
20
30
40
50
Ciclos de marés

L
=1,0MPa

L
=0,5MPa

L
=0,0MPa
 
F
o
r
ç
a
s
 
n
a
 
r
u
p
t
u
r
a
 
p
o
r
 
i
n
t
e
r
f
a
c
e
 
(
k
N
)
Nº de horas de envelhecimento
Salt fog cycles (5% of NaCl) Wet/Dry cycles (5% of NaCl)
Ageing hours Ageing hours
For L = 1.0MPa a 35.0% of degradation was
registered after 10,000h of exposure.
However, improvement of the rupture load
in the specimens with L = 0.5MPa was
registered after 10,000h of exposure.
For L = 1.0MPa a 12.5% of degradation was
registered after 10,000h of exposure.
In the others situations there was no 
significant variations after 10,000h of
exposure.
R
u
p
t
u
r
e
l
o
a
d
p
e
r
i
n
t
e
r
f
a
c
e
 
(
k
N
)
R
u
p
t
u
r
e
l
o
a
d
p
e
r
i
n
t
e
r
f
a
c
e
 
(
k
N
)
Experimental results
Experimental results
Salt fog cycles – 10,000h Wet/Dry cycles – 10,000h
Adhesive rupture! Adhesive rupture!
Reference – 0h
Cohesive rupture in the concrete!
The rupture surfaces of the specimens 
showed that the rupture mode changed 
from cohesive type by the concrete layer 
adjacent to the interface into adhesive type 
by the interface between both elements.
Rupture law
In order to study the GFRP/concrete interface and to establish a failure criterion 
based on the Mohr-Coulomb criterion, a research program is under development at 
Universidade Nova de Lisboa (UNL), based on double shear tests to obtain 
cohesion, c, and friction angle, . The figure below shows a typical envelope failure 
law (dotted line) defined according to equation:
 tan221  c
where 2 is the confinement or lateral stress and 21 is the shear stress.
Rupture lawSpecimens
Hours of
ageing Cohesion, c (MPa)
MC‐REF80‐01 0 1,97
Losses/
Gains
MC‐REF80‐02 0 1,81
MC‐REF80‐02a 0 1,56
Average value 0 1,78 ‐
MC‐NS‐01 3000 1,36 ‐23,60%
MC‐NS‐01a 3000 1,93 8,43%
MC‐NS‐02 3000 1,64 ‐7,87%
MC‐NS‐04 5000 1,41 ‐20,79%
MC‐NS‐04a 5000 2,01 12,88%
MC‐NS‐05 5000 1,99 11,80%
MC‐NS‐08 10000 1,91 7,30%
MC‐NS‐09 10000 1,47 ‐17,42%
MC‐MAR‐01 3000 1,65 ‐7,30%
MC‐MAR‐02 3000 1,43 ‐19,66%
MC‐MAR‐02a 3000 1,97 10,67%
MC‐MAR‐04 5000 1,99 11,80%
MC‐MAR‐05 5000 1,82 2,25%
MC‐MAR‐08 10000 1,07 ‐39,89%
MC‐MAR‐08a 10000 2,16 21,35%
MC‐MAR‐09 10000 1,85 3,93%
In terms of mean value, at 10,000h, the 
salt fog cycles revealed a degradation of 
5.1%.
However, for wet/dry cycles, ignoring the 
value obtained from the MC-MAR-08 
(1,07MPa), at 10,000h of exposure, 
cohesion increase almost 13%.
Note also that the variation of cohesion 
corresponds to the variation of the 
maximum bond stress in the specimens 
without lateral compression stress.
Rupture law
0 2000 4000 6000 8000 10000
0,00
0,25
0,50
0,75
1,00
1,25
1,50
 
Â
n
g
u
l
o
 
d
e
 
a
t
r
i
t
o
 
i
n
t
e
r
n
o
 
(
r
a
d
)
Nº de horas de envelhecimento
Ciclos de nevoeiro salino
0 2000 4000 6000 8000 10000
0,00
0,25
0,50
0,75
1,00
1,25
1,50
Ciclos de marés
 
Â
n
g
u
l
o
 
d
e
 
a
t
r
i
t
o
 
i
n
t
e
r
n
o
 
(
r
a
d
)
Nº de horas de envelhecimento
Ageing hoursAgeing hours
Salt fog cycles (5%  f N Cl) Wet/Dry cycles (5% of N Cl)
I
n
t
e
r
n
a
l
f
r
i
c
t
i
o
n
a
n
g
l
e
(
r
a
d
)
I
n
t
e
r
n
a
l
f
r
i
c
t
i
o
n
a
n
g
l
e
(
r
a
d
) 1.050
1.108
0.968
1.064 1.064
0.9830.961
1.061
Internal friction angle did not varied 
significantly. The greater variation  was 
calculated at 5,000h hour of exposure. 
However, at that time only one specimen 
was considered.
With 10,000h of exposure, the internal 
friction angle of the GFRP/concrete interface 
reduced only 1.3%.
After 5,000h of exposure, internal friction 
angle decreased approximately 10%.
Modeling with FE
So far, only the reference specimens were modulated with FE...
The concrete element discretization was done with 
quadrilateral elements with 15mm and, to precisely 
investigate the interfacial behaviour of the GFRP/concrete 
interface, the solid brick elements used to represent GFRP 
had 2.5mm near to the contact with concrete. A coarse 
mesh of 5.0mm was adopted for the GFRP element more 
distant from the contact. Compatibly mesh in the GFRP 
element was always guaranteed.
In order to avoid a model with a high number of FE, a 
quarter of the specimens were also considered based on 
the symmetric conditions of the tests. In total, 2411 3D 
elements were used corresponding to a total of 4956 
nodes. In the figure it is visible the standard model with the 
respectively mesh used in this work.
Modeling with FE
0 1 2 3 4 5 6 7 8
0
20
40
60
80
100
 
L
 = 0,0MPa
 
L
 = 0,5MPa
 
L
 = 1,0MPa
F
o
r
ç
a
 
T
o
t
a
l
 
(
k
N
)
Deslocamento (mm)
b
f
 = 80mm
0 1 2 3 4 5 6 7 8
0
20
40
60
80
100

L
 = 1.0MPa

L
 = 0.MPa
T
o
t
a
l
 
F
o
r
c
e
 
(
k
N
)
Displacement (mm)

L
 = 0MPa
1
T
o
t
a
l
 
F
o
r
c
e
 
(
k
N
)
Displacement (mm)
Specimen
σL
(MPa)
Fmax (kN) Error
(%)
δmax (mm) Error
(%)Exp. (*) ATENA 3D Exp. (*) ATENA 3D
MC‐REF80 0,0 16,06 17,57 9,40 2,20 2,05 ‐6,82
MC‐REF80 0,5 25,73 25,66 ‐0,27 3,14 3,10 ‐1,27
MC‐REF80 1,0 40,34 37,88 ‐6,10 5,18 4,40 ‐15,06
(*) Average values obtained from the experimental tests.
Modeling with FERigid interface
Gap interface
Principal maximum strains
Assuming a rigid GFRP/concrete interface is a somewhat 
crude manner of modelling an EBR concrete structure. 
Phenomena like slip, displacements between FRP and 
concrete, or normal and bond stress distribution along 
the interface are neglected.  Moreover, the rupture mode 
and even the rupture instant are only controlled by the 
experimental values of the ultimate strengths of all 
materials involved in the test. Nevertheless, the load 
versus displacements behaviour is quite stiffer when 
compared with the experimental or with the gap 
interface FE. The stress distribution along the GFRP is 
completely different when compared to the gap interface 
FE and, as explained above, the rupture mode occurs for 
the ultimate strain of the GFRP, i.e., for 2.20%. Hence, the 
rigid interface model cannot predict the rupture mode.
Modeling with FE
0,0 0,2 0,4 0,6 0,8 1,0
0
1
2
3
4
5
b
f
 = 80mm e 
L
 = 0,0MPa
EXT. 08
 
T
e
n
s
ã
o
 
d
e
 
a
d
e
r
ê
n
c
i
a
 
(
M
P
a
)
Deslizamento (mm)
 EXT. 01
 EXT. 02
 EXT. 03
 EXT. 04
 EXT. 05
 EXT. 06
 EXT. 07
 EXT. 08
 Ueda e
            Dai [38]
EXT. 01
0,0 0,2 0,4 0,6 0,8 1,0
0
1
2
3
4
5
b
f
 = 80mm e 
L
 = 0,5MPa
EXT. 08
 
T
e
n
s
ã
o
 
d
e
 
a
d
e
r
ê
n
c
i
a
 
(
M
P
a
)
Deslizamento (mm)
 EXT. 01
 EXT. 02
 EXT. 03
 EXT. 04
 EXT. 05
 EXT. 06
 EXT. 07
 EXT. 08
 Ueda e
            Dai [38]
EXT. 01
0,0 0,2 0,4 0,6 0,8 1,0
0
1
2
3
4
5
b
f
 = 80mm e 
L
 = 1,0MPa
EXT. 08
T
e
n
s
ã
o
 
d
e
 
a
d
e
r
ê
n
c
i
a
 
(
M
P
a
)
Deslizamento (mm)
EXT. 01
          EXT. 01   EXT. 02   EXT. 03
          EXT. 04   EXT. 05   EXT. 06
 EXT. 07   EXT. 08    Ueda e Dai [38]
Results obtained by Ueda and Dai 
methodology.
B
o
n
d
s
t
r
e
s
s
 
(
M
P
a
)
B
o
n
d
s
t
r
e
s
s
 
(
M
P
a
)
B
o
n
d
s
t
r
e
s
s
 
(
M
P
a
)
Slip (mm)
Slip (mm)
Slip (mm)
Modeling with FE
The principal strains in GFRP and concrete weren't reached at any step of the FEA and 
thus, the collapse of the shear tests weren't by rupture of these elements. This evidence 
leads to another, and unique, possible failure mode which is the debonding of the GFRP 
and concrete. Hence, the FEA also predicted with fairly agreement the rupture mode. The 
debonding phenomenon is quite visible in the model as shown in figure and it is in total 
accordance with the failure obtained in the experiments.
FE detail of the GFRP/concrete interface at maximum load 
(MC1‐FEA model ‐ vertical displacements amplified 10 
times).
bf = 80mm e σL = 0,0MPa bf = 80mm e σL = 0,5MPa bf = 80mm e σL = 1,0MPa
Modeling with FE
0 1 2 3 4 5 6 7
0
25
50
75
100
125
150
b
f
 = 80mm e 
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FE results at maximum load instant.
Modeling with FE
Applicable fields:
Externally Bonded Reinforcement (EBR) of Beams:
EBR of Slabs:
Teng’s work
Conclusions
1. The shear tests permitted to define parameters like cohesion and friction angle of the 
GFRP/concrete interface;
2. The proposed tests and obtained results may permit the estimation and quantification 
of different failure laws for different concrete classes and for different environmental 
ageing tests;
3. The rupture modes of the reference specimens were all essentially cohesive and in
concrete;
4. The number of the ageing hours lead to a change of the failure mode from cohesive
type to adhesive type. However, the specimens with a lateral compression stress 
involved some peeling that led to an increase of that stress for higher loads, i.e., at
instants closed to the specimen failure;
5. The results are the support for the definition of a failure envelope law that can be 
applied to FE of an interface based on the Mohr‐Coulomb failure criterion. Some 
preliminary results already showed a good accuracy and more efforts are now being 
done in order to improve the understanding of the influence of the surface treatment 
and the environmental ageing in those failure laws;
6. The interface FE may be applied in different concrete structures externally reinforced 
with GFRP.
Main conclusions are:
THANK YOU
The authors are grateful to Fundação para a Ciência e Tecnologia for partial financing of the
work under Project PTDC/ECM/100538/2008. The authors would like to thank for the help
of Prof. Vladimir Cervenka and Ing. Dobromil Pryl, with ATENA.
View
 publication stats
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 publication stats


Degradation of gfrp-plates bonded to concrete: An experimental approach based on mohr-coulomb failure criterion

Repositório da Universidade Nova de Lisboa

See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/268075078Degradation of GFRP‐plates bonded to concrete: An experimental approachbased on Mohr‐Coulomb failure criterionData · June 2011CITATIONS0READS453 authors:Some of the authors of this publication are also working on these related projects:Materials Failure Analysis with Case Studies from Oil and Gas Industries View projectPerformance and durability of CFRP Strengthened Steel Structures under Moisture and Thermal Effects View projectHugo BiscaiaNew University of Lisbon98 PUBLICATIONS   575 CITATIONS   SEE PROFILEManuel A G SilvaNew University of Lisbon136 PUBLICATIONS   1,072 CITATIONS   SEE PROFILECarlos ChastreNew University of Lisbon130 PUBLICATIONS   759 CITATIONS   SEE PROFILEAll content following this page was uploaded by Hugo Biscaia on 10 November 2014.The user has requested enhancement of the downloaded file.Degradation of GFRP‐plates bonded to concrete: An experimental approach based on Mohr‐Coulombfailure criterionHugo Biscaia, Manuel Gonçalves da Silva & Carlos ChastreFaculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, PortugalObjectives of the study1. Characterize the glass FRP/concrete interface by double shear tests;2. Analyse the degradation imposed to the GFRP/concrete interface by humidity salted environments;3. The lack of information about the modelling of the interface between FRPs and concrete is a very actual theme and this work is a contribution to mitigate this gap. However, at this point of the study only reference specimens were modulated, i.e., without ageing.4. Make proposals in order to adjust some rules or national codes.An experimental programme was conducted in order to:Accelerated ageing tests0 1 2 3 4 5 6 70,00,51,01,5DryNo. of days Wet/Dry cyclesWetWet and dry cycles  with 5% of salt0 50 100 150 200 250 300 350 400 45001020304050  Temperature Relative HumidityTime (days)Temperature (ºC)020406080100Relative Humidity (%)Accelerated ageing testsSalt fog cycles (5% of salt)0 4 8 12 16 20 2401DryNo. of hours Salt fog cyclesFogFogDryNo. of hoursSurface treatmentDry sand blasting with 4 bar of pressure.Proposed shear testsCharacterization of materials0,0 0,2 0,4 0,6 0,8 1,00510152025 fc,cub (MPa)c (%)28 DaysConcrete  strength0 1 2 30100200300400500600 ff (MPa)f (%)Tensile strength of the GFRP flat couponsfcm,cub(MPa)fcm(MPa)fctm (*)(MPa)c1 (*) (%)fctm,sp (*) (MPa)Ecm(*)(GPa)18.6 16.9 1.65 0.17 1.83 23.18Concrete  properties:Flatcouponsεf m(%)ffm(MPa)Ef m (MPa)Reference 2.20 513.9 23.49GFRP  properties:(*) According to EC2.Experimental testsSpecimenFmax (kN) δmax (mm)Média MédiaMC‐REF80‐01 17.8616.062.602.20MC‐REF80‐02 16.28 2.10MC‐REF80‐02a 14.03 1.91MC‐REF20‐01 4.38(*)4.964.372.95MC‐REF20‐02 5.55(**) 6.00MC‐REF80‐03 25.73 25.73 2.25 3.14MC‐REF80‐04 34.5640.343.655.18MC‐REF80‐04a 46.12 3.14(*) Fmax = 17.51kN multiplying by 4 (GFRP with 1/4 of the wide ofother specimens).(**) Fmax = 22.19kN multiplying by 4 (GFRP with 1/4 of the wideof other specimens).0 1 2 3 4 5 6 7 8020406080100L = 1.0MPaL = 0.MPaTotal Force (kN)Displacement (mm)L = 0MPaReference specimens (at 0h of exposure).5MPaPreliminary considerationsCalculating maximum bond stress…From equilibrium and compatibility conditions of a finite element of FRP with length dx, it is obtained:Assumptions:i) εf = ds/dx, and εf is the FRP strain;ii) linear and elastic behaviour is assumed for GFRP;iii) bond is associated only with shear stresses, i.e., the normal stresses, σn, shown in figure above are considered of no influence.  022ff tEsdxsd where s is the slip between FRP and concrete, τ(s) is the local bond stress, x is the coordinate axis along the bonded length, Ef and tf, respectively, the Young modulus and the thickness of the FRP.Preliminary considerationsCalculating maximum bond stress… maxsel smaxBond stress, Slip, s a) Linear law b) Bi-linear lawmaxmaxskuelu sskmaxmaxʹ ff AEFdxds0dxdsAssuming, for instance, the ascending branch of the bilinear bond‐slip law and introducing the boundary conditions of the problem:where Af is the transversal area of the GFRP and Leff is the effective bond length, the solution is given by:at x = 0at x = Leff   effefffff LLx‐tbEFxs sinhcosh   effefff LLxbFxsinhcosh   2coth20avgmax xeffbLLandPreliminary considerationsCalculating maximum bond stress…0 1 2 3 4 5012345678 Eq. 18 =  max/avg = lb/leffeffbLL  2coth20avgmax xctmffeff fctEL2Equation proposed by fib Bulletin 14 where c2 = 2.0 in the case of CFRP. In the case of GFRP, previous work, led to c2 = 0.8.Preliminary considerationsComparing the maximum bond stress expected with some experimental works…0 2 4 6 8 100246810+40%+20%‐40%‐20%GFRP  max(a)  (MPa)max previsto (MPa) Biscaia [23]  Aiello e Leone [96]  Mukhopadhyaya et al. [98] Lucas [144]  Projecto PTDC/ECM/100538/2011 [182]expec ed (MPa)Experimental resultsReferencespecimensLateral compression stress,     (MPa) τmed (MPa) τmax (MPa)MC‐REF80‐01 0.0 0.691 1.296 1.52 1.97MC‐REF80‐02 0.0 0.682 1.288 1.40 1.81MC‐REF80‐02a 0.0 0.682 1.288 1.21 1.56MC‐REF20‐01 0.0 0.706 1.309 1.46 1.91MC‐REF20‐02 0.0 0.706 1.309 1.85 2.42MC‐REF80‐03 0.5 0.687 1.292 2.20 2.85MC‐REF80‐04 1.0 0.699 1.303 2.91 3.79MC‐REF80‐04a 1.0 0.689 1.294 3.94 5.09effbLLavg maxL1.78MPa2.85MPa4.44MPaMPa0.0max5.2 MPa0.0max6.1 0 2000 4000 6000 8000 1000001020304050L=1,0MPaL=0,5MPa Forças na ruptura por interface (kN)Nº de horas de envelhecimentoL=0,0MPaCiclos de nevoeiro salino0 2000 4000 6000 8000 1000001020304050Ciclos de marésL=1,0MPaL=0,5MPaL=0,0MPa Forças na ruptura por interface (kN)Nº de horas de envelhecimentoSalt fog cycles (5% of NaCl) Wet/Dry cycles (5% of NaCl)Ageing hours Ageing hoursFor L = 1.0MPa a 35.0% of degradation wasregistered after 10,000h of exposure.However, improvement of the rupture loadin the specimens with L = 0.5MPa wasregistered after 10,000h of exposure.For L = 1.0MPa a 12.5% of degradation wasregistered after 10,000h of exposure.In the others situations there was no significant variations after 10,000h ofexposure.Ruptureloadperinterface (kN)Ruptureloadperinterface (kN)Experimental resultsExperimental resultsSalt fog cycles – 10,000h Wet/Dry cycles – 10,000hAdhesive rupture! Adhesive rupture!Reference – 0hCohesive rupture in the concrete!The rupture surfaces of the specimens showed that the rupture mode changed from cohesive type by the concrete layer adjacent to the interface into adhesive type by the interface between both elements.Rupture lawIn order to study the GFRP/concrete interface and to establish a failure criterion based on the Mohr-Coulomb criterion, a research program is under development at Universidade Nova de Lisboa (UNL), based on double shear tests to obtain cohesion, c, and friction angle, . The figure below shows a typical envelope failure law (dotted line) defined according to equation: tan221  cwhere 2 is the confinement or lateral stress and 21 is the shear stress.Rupture lawSpecimensHours ofageing Cohesion, c (MPa)MC‐REF80‐01 0 1,97Losses/GainsMC‐REF80‐02 0 1,81MC‐REF80‐02a 0 1,56Average value 0 1,78 ‐MC‐NS‐01 3000 1,36 ‐23,60%MC‐NS‐01a 3000 1,93 8,43%MC‐NS‐02 3000 1,64 ‐7,87%MC‐NS‐04 5000 1,41 ‐20,79%MC‐NS‐04a 5000 2,01 12,88%MC‐NS‐05 5000 1,99 11,80%MC‐NS‐08 10000 1,91 7,30%MC‐NS‐09 10000 1,47 ‐17,42%MC‐MAR‐01 3000 1,65 ‐7,30%MC‐MAR‐02 3000 1,43 ‐19,66%MC‐MAR‐02a 3000 1,97 10,67%MC‐MAR‐04 5000 1,99 11,80%MC‐MAR‐05 5000 1,82 2,25%MC‐MAR‐08 10000 1,07 ‐39,89%MC‐MAR‐08a 10000 2,16 21,35%MC‐MAR‐09 10000 1,85 3,93%In terms of mean value, at 10,000h, the salt fog cycles revealed a degradation of 5.1%.However, for wet/dry cycles, ignoring the value obtained from the MC-MAR-08 (1,07MPa), at 10,000h of exposure, cohesion increase almost 13%.Note also that the variation of cohesion corresponds to the variation of the maximum bond stress in the specimens without lateral compression stress.Rupture law0 2000 4000 6000 8000 100000,000,250,500,751,001,251,50 Ângulo de atrito interno (rad)Nº de horas de envelhecimentoCiclos de nevoeiro salino0 2000 4000 6000 8000 100000,000,250,500,751,001,251,50Ciclos de marés Ângulo de atrito interno (rad)Nº de horas de envelhecimentoAgeing hoursAgeing hoursSalt fog cycles (5%  f N Cl) Wet/Dry cycles (5% of N Cl)Internalfrictionangle(rad)Internalfrictionangle(rad) 1.0501.1080.9681.064 1.0640.9830.9611.061Internal friction angle did not varied significantly. The greater variation  was calculated at 5,000h hour of exposure. However, at that time only one specimen was considered.With 10,000h of exposure, the internal friction angle of the GFRP/concrete interface reduced only 1.3%.After 5,000h of exposure, internal friction angle decreased approximately 10%.Modeling with FESo far, only the reference specimens were modulated with FE...The concrete element discretization was done with quadrilateral elements with 15mm and, to precisely investigate the interfacial behaviour of the GFRP/concrete interface, the solid brick elements used to represent GFRP had 2.5mm near to the contact with concrete. A coarse mesh of 5.0mm was adopted for the GFRP element more distant from the contact. Compatibly mesh in the GFRP element was always guaranteed.In order to avoid a model with a high number of FE, a quarter of the specimens were also considered based on the symmetric conditions of the tests. In total, 2411 3D elements were used corresponding to a total of 4956 nodes. In the figure it is visible the standard model with the respectively mesh used in this work.Modeling with FE0 1 2 3 4 5 6 7 8020406080100 L = 0,0MPa L = 0,5MPa L = 1,0MPaForça Total (kN)Deslocamento (mm)bf = 80mm0 1 2 3 4 5 6 7 8020406080100L = 1.0MPaL = 0.MPaTotal Force (kN)Displacement (mm)L = 0MPa1Total Force (kN)Displacement (mm)SpecimenσL(MPa)Fmax (kN) Error(%)δmax (mm) Error(%)Exp. (*) ATENA 3D Exp. (*) ATENA 3DMC‐REF80 0,0 16,06 17,57 9,40 2,20 2,05 ‐6,82MC‐REF80 0,5 25,73 25,66 ‐0,27 3,14 3,10 ‐1,27MC‐REF80 1,0 40,34 37,88 ‐6,10 5,18 4,40 ‐15,06(*) Average values obtained from the experimental tests.Modeling with FERigid interfaceGap interfacePrincipal maximum strainsAssuming a rigid GFRP/concrete interface is a somewhat crude manner of modelling an EBR concrete structure. Phenomena like slip, displacements between FRP and concrete, or normal and bond stress distribution along the interface are neglected.  Moreover, the rupture mode and even the rupture instant are only controlled by the experimental values of the ultimate strengths of all materials involved in the test. Nevertheless, the load versus displacements behaviour is quite stiffer when compared with the experimental or with the gap interface FE. The stress distribution along the GFRP is completely different when compared to the gap interface FE and, as explained above, the rupture mode occurs for the ultimate strain of the GFRP, i.e., for 2.20%. Hence, the rigid interface model cannot predict the rupture mode.Modeling with FE0,0 0,2 0,4 0,6 0,8 1,0012345bf = 80mm e L = 0,0MPaEXT. 08 Tensão de aderência (MPa)Deslizamento (mm) EXT. 01 EXT. 02 EXT. 03 EXT. 04 EXT. 05 EXT. 06 EXT. 07 EXT. 08 Ueda e            Dai [38]EXT. 010,0 0,2 0,4 0,6 0,8 1,0012345bf = 80mm e L = 0,5MPaEXT. 08 Tensão de aderência (MPa)Deslizamento (mm) EXT. 01 EXT. 02 EXT. 03 EXT. 04 EXT. 05 EXT. 06 EXT. 07 EXT. 08 Ueda e            Dai [38]EXT. 010,0 0,2 0,4 0,6 0,8 1,0012345bf = 80mm e L = 1,0MPaEXT. 08Tensão de aderência (MPa)Deslizamento (mm)EXT. 01          EXT. 01   EXT. 02   EXT. 03          EXT. 04   EXT. 05   EXT. 06 EXT. 07   EXT. 08    Ueda e Dai [38]Results obtained by Ueda and Dai methodology.Bondstress (MPa)Bondstress (MPa)Bondstress (MPa)Slip (mm)Slip (mm)Slip (mm)Modeling with FEThe principal strains in GFRP and concrete weren't reached at any step of the FEA and thus, the collapse of the shear tests weren't by rupture of these elements. This evidence leads to another, and unique, possible failure mode which is the debonding of the GFRP and concrete. Hence, the FEA also predicted with fairly agreement the rupture mode. The debonding phenomenon is quite visible in the model as shown in figure and it is in total accordance with the failure obtained in the experiments.FE detail of the GFRP/concrete interface at maximum load (MC1‐FEA model ‐ vertical displacements amplified 10 times).bf = 80mm e σL = 0,0MPa bf = 80mm e σL = 0,5MPa bf = 80mm e σL = 1,0MPaModeling with FE0 1 2 3 4 5 6 70255075100125150bf = 80mm e L = 0,0MPaTensões de aderência (MPa)151510 25% Fmax   50% Fmax 75% Fmax   FmaxEXT. 09EXT. 01Comprimento de colagem (mm)Bond stresses (MPa)Bondlength(mm)0 1 2 3 4 5 6 70255075100125150bf = 80mm e L = 0,5MPa151Tensões de aderência (MPa)510 25% Fmax   50% Fmax 75% Fmax   FmaxEXT. 09EXT. 01Comprimento de colagem (mm)Bond stresses (MPa)Bondlength(mm)0 1 2 3 4 5 6 70255075100125150151bf = 80mm e L = 1,0MPaComprimento de colagem (mm)Tensões de aderência (MPa)510 25% Fmax   50% Fmax 75% Fmax   FmaxEXT. 09EXT. 01Bondlength(mm)Bond stresses (MPa)FE results at maximum load instant.Modeling with FEApplicable fields:Externally Bonded Reinforcement (EBR) of Beams:EBR of Slabs:Teng’s workConclusions1. The shear tests permitted to define parameters like cohesion and friction angle of the GFRP/concrete interface;2. The proposed tests and obtained results may permit the estimation and quantification of different failure laws for different concrete classes and for different environmental ageing tests;3. The rupture modes of the reference specimens were all essentially cohesive and inconcrete;4. The number of the ageing hours lead to a change of the failure mode from cohesivetype to adhesive type. However, the specimens with a lateral compression stress involved some peeling that led to an increase of that stress for higher loads, i.e., atinstants closed to the specimen failure;5. The results are the support for the definition of a failure envelope law that can be applied to FE of an interface based on the Mohr‐Coulomb failure criterion. Some preliminary results already showed a good accuracy and more efforts are now being done in order to improve the understanding of the influence of the surface treatment and the environmental ageing in those failure laws;6. The interface FE may be applied in different concrete structures externally reinforced with GFRP.Main conclusions are:THANK YOUThe authors are grateful to Fundação para a Ciência e Tecnologia for partial financing of thework under Project PTDC/ECM/100538/2008. The authors would like to thank for the helpof Prof. Vladimir Cervenka and Ing. Dobromil Pryl, with ATENA.View publication statsView publication stats

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Degradation of gfrp-plates bonded to concrete: An experimental approach based on mohr-coulomb failure criterion

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