ACIC - 2002Advanced Polymer Composites for Structural
Applications in Construction15-17 April 2002
Southampton, U.K.
CRACKING ANALYSIS OF FRP REINFORCED CONCRETE
TENSION MEMBERS
CRACKING ANALYSIS OF FRP CRACKING ANALYSIS OF FRP REINFORCED CONCRETE REINFORCED CONCRETE
TENSION MEMBERSTENSION MEMBERS
M.A. AIELLO,M.A. AIELLO, M. LEONE, L.OMBRES
Department of Innovation EngineeringUniversity of Lecce
Lecce, Italy
ACIC - 2002 Advanced Polymer Composites for Structural Applications in Construction
15-17 April 2002 - Southampton, U.K.
Cracking analysis of FRP reinforced concrete tension membersM.A. Aiello, M. Leone & L. Ombres
Department of Innovation Engineering, University of Lecce, Lecce, Italy
FRP REINFORCED CONCRETE STRUCTURESFRP REINFORCED CONCRETE STRUCTURES
High Strength
Low weight
Good Durability
High Deformability
Lack of Ductility
High Crack Width
SERVICEABILITY BEHAVIOUR:THE CONTROLLING DESIGN CONDITION
ACCURATE EVALUATION OF CRACKING AND DEFORMABILITY
TENSION STIFFENING CONTRIBUTION
ACIC - 2002 Advanced Polymer Composites for Structural Applications in Construction
15-17 April 2002 - Southampton, U.K.
Cracking analysis of FRP reinforced concrete tension membersM.A. Aiello, M. Leone & L. Ombres
Department of Innovation Engineering, University of Lecce, Lecce, Italy
SCOPESSCOPES
Evaluation of the tension stiffening of FRP reinforced concrete members
varying main geometrical and mechanical parameters
by comparison between theoretical and experimental results
Definition of theoretical models and effectiveness check
Calibration of relationships useful from a design point of view
ACIC - 2002 Advanced Polymer Composites for Structural Applications in Construction
15-17 April 2002 - Southampton, U.K.
Cracking analysis of FRP reinforced concrete tension membersM.A. Aiello, M. Leone & L. Ombres
Department of Innovation Engineering, University of Lecce, Lecce, Italy
EXPERIMENTAL ANALYSISEXPERIMENTAL ANALYSIS
FRP reinforced concrete members subjected to axial tension
Variable parameter: CONFINAMENT ACTIONCONFINAMENT ACTION
Thickness of the concreteembedding the FRPreinforcement
THEORETICAL ANALYSISTHEORETICAL ANALYSIS
Perfect bond between the concrete and the reinforcement
Presence of slip between the concrete and the
reinforcement
ACIC - 2002 Advanced Polymer Composites for Structural Applications in Construction
15-17 April 2002 - Southampton, U.K.
Cracking analysis of FRP reinforced concrete tension membersM.A. Aiello, M. Leone & L. Ombres
Department of Innovation Engineering, University of Lecce, Lecce, Italy
EXPERIMENTAL SETEXPERIMENTAL SET--UPUP
FRP rebar
LVDT LVDT
Test set-up
Concrete block
Two LVDT have been used:
• to measure the elongation of the rebars
ACIC - 2002 Advanced Polymer Composites for Structural Applications in Construction
15-17 April 2002 - Southampton, U.K.
Cracking analysis of FRP reinforced concrete tension membersM.A. Aiello, M. Leone & L. Ombres
Department of Innovation Engineering, University of Lecce, Lecce, Italy
MATERIALS
Mechanical properties of concrete:• compression strength fc= 46,82 MPa• tensile strength fct = 4,35 MPa
Mechanical properties of CFRP rebars:• ultimate strength fu= 2401 MPa• elastic modulus E = 109790 MPa
0
100
200
300
400
500
600
700
800
900
1000
0 0,001 0,002 0,003 0,004 0,005 0,006ε
σ (MPa)
Utilized rebars: externally sanded and spiral wounded with fibers
EXPERIMENTAL PROGRAM
60450T60A, T60B2
80450T80A, T80B2
50450T50A, T50B2
40450T40A, T40B2
Nominal Diameter
(mm)
Height (mm)SpecimensNumber of
specimens
ACIC - 2002 Advanced Polymer Composites for Structural Applications in Construction
15-17 April 2002 - Southampton, U.K.
Cracking analysis of FRP reinforced concrete tension membersM.A. Aiello, M. Leone & L. Ombres
Department of Innovation Engineering, University of Lecce, Lecce, Italy
EXPERIMENTAL RESULTSEXPERIMENTAL RESULTS
0
10
20
30
40
50
60
70
0 0,005 0,01 0,015Strain
App
lied
tens
ion
load
(kN
)
T50BNaked bar
0
10
20
30
40
50
60
70
80
0 0,005 0,01 0,015Strain
App
lied
tens
ion
load
(kN
)
T60B Rebar
Force vs deformation for tensile members and rebars – T50B
Force vs deformation for tensile members and rebars – T60B
ACIC - 2002 Advanced Polymer Composites for Structural Applications in Construction
15-17 April 2002 - Southampton, U.K.
Cracking analysis of FRP reinforced concrete tension membersM.A. Aiello, M. Leone & L. Ombres
Department of Innovation Engineering, University of Lecce, Lecce, Italy
EXPERIMENTAL RESULTSEXPERIMENTAL RESULTS
15,012,510,07,55,02,50,00
10
20
30
40
50
60
70
80
Strain
App
lied
tens
ion
load
T60B
T80B
T50B
T40B Naked bar
(kN
)
(x 1000)
The rebars embedded in the concrete cylinder present a higher stiffness at all stress levels
The scatters between curves reduce above a certainamount of confinement
ACIC - 2002 Advanced Polymer Composites for Structural Applications in Construction
15-17 April 2002 - Southampton, U.K.
Cracking analysis of FRP reinforced concrete tension membersM.A. Aiello, M. Leone & L. Ombres
Department of Innovation Engineering, University of Lecce, Lecce, Italy
EXPERIMENTAL RESULTSEXPERIMENTAL RESULTS
Numbers of cracks vs tensile specimens diameter
0
0,5
1
1,5
2
2,5
3
30 50 70 90Tensile specimens diameter (mm)
Cra
cks
open
ing
(mm
)
0
1
2
3
4
5
6
7
8
9
30 50 70 90Tensile specimens diameter (mm)
Num
bers
of c
rack
s
Cracks opening vs tensile specimens diameter
ACIC - 2002 Advanced Polymer Composites for Structural Applications in Construction
15-17 April 2002 - Southampton, U.K.
Cracking analysis of FRP reinforced concrete tension membersM.A. Aiello, M. Leone & L. Ombres
Department of Innovation Engineering, University of Lecce, Lecce, Italy
THEORETICAL ANALYSISTHEORETICAL ANALYSIS
Model adopted in the Eurocode2 for steel reinforced concrete members
Analytical model on the hypothesis of perfect bond
Analytical model removing the hypothesis of perfect bond
THE ANALYTICAL MODEL THE ANALYTICAL MODEL –– PERFECT BONDPERFECT BONDBernoulli hypothesis up to failure The section remains plane after
deformation
The distribution along the reinforcement of the bond stress is uniform
The costitutive laws of the FRP and the tensile concrete are linear with the Young’s modulus
The tensile force corresponding to the first cracking of the specimens is
( )µnAfF cctcr += 1Where: Fct=tensile strength of the concrete; Ac=concrete specimens area; µ=Ar/Ac= percentage of tensile reinforcement; Ar=FRP reinforcement area; n=Er/Ect=ratio between the elastic moduli of the FRP and the tensile concrete respectively
The equilibrium condictions in the cracking stage, F>Fcr are
Equilibrium condiction for cross section Axial equilibrium for FRP rebars
( ) dzpzzd r τσ =)(rrcc AAF σσ +=
ACIC - 2002 Advanced Polymer Composites for Structural Applications in Construction
15-17 April 2002 - Southampton, U.K.
Cracking analysis of FRP reinforced concrete tension membersM.A. Aiello, M. Leone & L. Ombres
Department of Innovation Engineering, University of Lecce, Lecce, Italy
THEORETICAL RELATIONSHIPTHEORETICAL RELATIONSHIP
ANALYTICAL MODELANALYTICAL MODEL
area specimens concrete
concrete; theofstrength tensile ,
rebar theofperimeter stress bondmax
areaent reinforcem FRPforce applied
entreinforcem FRP of modulo elasticstrainent reinforcem of mean value
min
=
==
======
c
ctad
cct
ad
r
r
m
A
fp
Afl
p
AFE
τ
τ
ε
−=
min
21lpA
FE
ad
rr
m
τε Where:
DESIGN MODELDESIGN MODEL
loads) mshort terfor 1( duration load on the dependent coefficent
coefficentquality bond
section cracked in therebar in thetension
rebar in thetension ent reinforcem ofstrain average
2
2
1
===
==
==
βββ
σ
σε
r
crsr
s
sm
AF
−=
2
211s
sr
r
ssm E σ
σββ
σε
ACIC - 2002 Advanced Polymer Composites for Structural Applications in Construction
15-17 April 2002 - Southampton, U.K.
Cracking analysis of FRP reinforced concrete tension membersM.A. Aiello, M. Leone & L. Ombres
Department of Innovation Engineering, University of Lecce, Lecce, Italy
COMPARISON BETWEEN THEORETICAL COMPARISON BETWEEN THEORETICAL MODELS AND EXPERIMENTAL RESULTSMODELS AND EXPERIMENTAL RESULTS
98765432100
10
20
30
40
50
Strain
App
lied
tens
ion
load
Naked
EC2
Theor.
Exp
(x 1000)
(kN
)
Theoretical-experimental comparison for the T40B specimens
The analytical model and the Code model predict satisfactory the experimental results
ACIC - 2002 Advanced Polymer Composites for Structural Applications in Construction
15-17 April 2002 - Southampton, U.K.
Cracking analysis of FRP reinforced concrete tension membersM.A. Aiello, M. Leone & L. Ombres
Department of Innovation Engineering, University of Lecce, Lecce, Italy
COMPARISON BETWEEN THEORETICAL COMPARISON BETWEEN THEORETICAL MODELS AND EXPERIMENTAL RESULTSMODELS AND EXPERIMENTAL RESULTS
1210864200
10
20
30
40
50
60
70
( x 1000)
App
lied
tens
ion
load
Exp
Theoretical
Naked
(kN
)
Strain
EC2
Theoretical-experimental comparison for the T60A specimens
Analytical and Code predictions overstimate deformability for high values of applied force while they are in good agreement with experimental results at lower levels of applied force
ACIC - 2002 Advanced Polymer Composites for Structural Applications in Construction
15-17 April 2002 - Southampton, U.K.
Cracking analysis of FRP reinforced concrete tension membersM.A. Aiello, M. Leone & L. Ombres
Department of Innovation Engineering, University of Lecce, Lecce, Italy
COMPARISON BETWEEN THEORETICAL COMPARISON BETWEEN THEORETICAL MODELS AND EXPERIMENTAL RESULTSMODELS AND EXPERIMENTAL RESULTS
15.012.510.07.55.02.50.00
20
40
60
Strain
App
lied
tens
ion
load
Experimental
Theoretical
EC2
Naked
(kN
)
(x 1000)
80
Theoretical-experimental comparison for the T80B specimens
Analytical predictions are in very good agreement with experiments while the Code predictions understimate deformability values for high level of applied force
ACIC - 2002 Advanced Polymer Composites for Structural Applications in Construction
15-17 April 2002 - Southampton, U.K.
Cracking analysis of FRP reinforced concrete tension membersM.A. Aiello, M. Leone & L. Ombres
Department of Innovation Engineering, University of Lecce, Lecce, Italy
CONCLUSIONSCONCLUSIONS
The tension stiffening contribution is very influential and effective in reducing the strain of FRP reinforcing rebars;
The ratio concrete cover-to-rebar diameter influences the tension stiffening. The value c/d=3 seems to be the optimal value;
Models founded on the Bernouilli hypothesis are able to predict the behaviour of tension FRP reinforced concrete elements;
The Eurocode model, calibrated for the analysis of steel reinforced concrete members can be used for the analysis of FRP reinforced concrete members by introducing an adequate value of bond coefficent
ACIC - 2002 Advanced Polymer Composites for Structural Applications in Construction
15-17 April 2002 - Southampton, U.K.
Cracking analysis of FRP reinforced concrete tension membersM.A. Aiello, M. Leone & L. Ombres
Department of Innovation Engineering, University of Lecce, Lecce, Italy
FUTURE DEVELOPMENTSFUTURE DEVELOPMENTS
Further experimental investigation considering the influence of the other parameters, such as the strength of the concrete, the type of FRP rebars, the outer surface treatment of FRP rebars
Definition of a theoretical model that takes into account the slip between reinforcement and concrete
