05 Research Dapped-Ends Nagy-Gyorgy T
Transcript of 05 Research Dapped-Ends Nagy-Gyorgy T
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THEORETICAL AND EXPERIMENTAL STUDY
SUPPORT ZONE STRENGTHENED
NAGY-GY RGY TamsLecturer, PhD
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RESEARCHRESEARCH SIGNIFICANCESIGNIFICANCE
appe -en eams are w e y use n precas concre e u ngs
and bridges, thus one span elements being supported on
columns, pylons or longitudinal beams.
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RESEARCHRESEARCH SIGNIFICANCESIGNIFICANCE
For this type of beams, there were identified five potential failure modes:
(1) flexure (cantilever bending) and axial tension in the extended end
2 direct shear at the unction between the da ed and unda ed zone of the member
(3) diagonal tension on the re-entrant corner(4) diagonal tension in the extended end and
(5) diagonal tension in undapped zone
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RESEARCHRESEARCH SIGNIFICANCESIGNIFICANCE
The research program has been performed in the following steps:
predimensioning and detailing the element,
numerical anal sis with finite element and strut-and-tie methods,
experimental testing on four dapped beam ends strengthened with
FRP composite
interpreting the results and preparing the conclusions
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DIMENSIONINGDIMENSIONING AND DETAILING OF THE ELEMENTAND DETAILING OF THE ELEMENT
Preliminary dimensioning and detailing of the studied dapped beam
end were made according tothe Romanian codes and verified
with those from EC2, ACI318 and PCI Design Handbook, in
order to attain the bearing capacity of 80 t (800 kN).
Beams height - 150 cm,
Dapped zone 80/80 cm
.
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DIMENSIONINGDIMENSIONING AND DETAILING OF THE ELEMENTAND DETAILING OF THE ELEMENT
2
2
1-1 2-21 22
2
12
2
12
90
80
12
2
66
12
701
2
1
66
2 1
1 80
251 50
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NUMERICAL ANALYSISNUMERICAL ANALYSIS
In the theoretical model, there were used the characteristic
strengths of the concrete and the steel reinforcement.
We used three main methods for the analysis:
- Elastic analysis using the AxisVM program
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- Strut-and-Tie models
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ElasticElastic AnalysisAnalysis
was per orme us ng n e e emen program x s . ere were
obtained the level and the distribution of stresses in concrete. The load
level corresponding to the yielding limit in the horizontal reinforcement
.
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NonlinearNonlinear AnalysisAnalysis
was per orme us ng so ware, resu ng e crac pa ern
at different load levels, the failure load and the collapse mechanism of the
element. Yielding in the horizontal reinforcement started at the load level
.
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StrutStrut--andand--TieTie ModelsModels
Due to the fact that in our case the steel reinforcement was known,
the analysis was performed to determine the maximum force in
the element when the horizontal bars from the dapped-end are
starting to yield. In this assumption, there were used several
models which can approximate accurately the studied zone. The
maximum force at which the most tensioned reinforcement started
to yield was 94 t.
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NUMERICAL ANALYSISNUMERICAL ANALYSIS
ELASTIC (AXIS VM) NON-LINEAR (BIOGRAF) STRUT-AND-TIE
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EXPERIMENTALEXPERIMENTAL PROGRAMPROGRAM
Two dapped beams with the same dimensions and internal reinforcement
were manufactured; the mid-span was over-reinforced. Before casting,
two strain gages were added nearly the re-entrant corner, one to the
or zon a re n orcemen an e o er o e ver ca s rrup .
80
VIEW
NTVIE
70
0
175 100
SID
RC
FR
7
FLOOR
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STRENGTHENINGSTRENGTHENING OF THE ELEMENTSOF THE ELEMENTS
CALE
-ENDS
C1 PRIOR TO FAILURE (REFERENCE)
C2
4FUL
L
DAPP
E
C3
UP TO 800 KN (SERVICEABILITY)C4
STRENGTHENING 3 SYSTEMS OF CFRP COMPOSITES
AIM TO INCREASE THE SERVICE LOAD BY 20%.
,
FABRIC APPLIED ON BOTH SIDES IN 45/0/90 DIRECTIONS
RC2 /RC4 10 CM WIDE CFRP PLATES APPLIED IN 45/ 90RESPECTIVELY IN 0/ 90 DIRECTION, ON BOTH SIDES
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FRPFRP COMPOSITE SYSTEMSCOMPOSITE SYSTEMS
System Components
Tensile
Strength
[N/mm2]
Tensile
Modulus
[N/mm2]
Strain at
Failure
[]
System 1
(RC1)
a rap a r c
SikaDur 330 Resin 30 3800 -
ys em
(RC2/
RC4)
SikaDur 30 Resin 30 12800 -
System 3
(RC3)
SikaWrap 400C HiMod NW Fabric 2600 640000 4
SikaDur 300 Resin 45 3500 15
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TEST RESULTSTEST RESULTS 11STST PHASEPHASE
The elements showed a similar behaviour with respect to the
maximum force and deflection. The design value of the
serviceability limit state was of 80 t.
For this value of the experimental load:
(a)the stress level recorded in the reinforcement was
comparable for all the elements;
,
very close to the initial starting point;
(c)it was noted a good similarity between the crack pattern for
a e spec mens, e genera aspec e ng en ca ;
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TEST RESULTSTEST RESULTS 22NDND PHASEPHASE C1/RC1C1/RC1
Specimen C1 was tested close to failure and served as control element.
- The first crack started at an angle of 60, from the re-entrant corner and up to 74 t
did not appear other. The final crack pattern was uniformly distributed around the re-
entrant corner, as expected. The first crack had the major width (approx. 3.5 mm).
- The maximum displacement was 30 mm, the remanent was 14 mm. Strain gages
attached to reinforcement did not function. The peak load was 160 t.
- After that, the specimen was retrofitted and retested.
The specimen RC1 had a linear behaviour up to 160 t, when there were observed the first
fibre ruptures.
- The maximum reached load was 178 t and after that it followed a long yielding level
(approx. 14 mm) until collapse. The failure was ductile, produced by successive
rea ng o e car on res a ong a pr nc pa crac an no ue o re e on ng ordelamination.
- In the same time concrete crushed in the compressed zone at the maximum load.
.
fibres reached the maximum values.
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TEST RESULTSTEST RESULTS 22NDND PHASEPHASE C1/RC1C1/RC1
100
120
140
160
[t]
20
40
60
80LOA
C1
RC10
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36
DISPLACEMENT [mm]
180
2
13
100
120
140
160
D
[t]
G3 - RC1
G4 - RC1
G5 - RC1
G6 - RC1
V20
40
60
80
L
O
G4/G6
G3/G5
0 2 4 6 8 10 12 14 16 18 20 22
STRAIN []
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TEST RESULTSTEST RESULTS 22NDND PHASEPHASE C1/RC1C1/RC1
100
120
140
160
[t]
20
40
60
80LOA
C1
RC10
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36
DISPLACEMENT [mm]
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TEST RESULTSTEST RESULTS 22NDND PHASEPHASE C2/RC2C2/RC2
.- The first crack started at a 42 angle from the re-entrant corner and up to 65 t it did
not appear others. At this load level there developed four major cracks, but their
openings were not significant.
- The maximum displacement was 6 mm, the remanent was 2 mm. Strain gages
attached to the steel reinforcement (S1) indicated 1.87 , which meant that it was atthe yielding level. After that the specimen was retrofitted and retested.
The specimen RC2 had a linear behaviour up to 130 t, when, beside some cracks, it
developed a crack around the inclined plates, which, for a small increase in load (143
t), determined the peeling-off.- The element resisted up to 176 t, when also the vertical plates failed through
peeling-off. The failure was brittle at the maximum displacement of 20 mm, the
remament being 5 mm.
- The maximum measured strain in steel reinforcement was 2.59 at 148 t and 1.87
at 116 t, which indicated an increase of service load by 45 %, compared with thesame strain level of the reference specimen (C2).
- The maximum strain in composite reached 7 , which correspond to 41 % of the
com osites ultimate value.
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TEST RESULTSTEST RESULTS 22NDND PHASEPHASE C2/RC2C2/RC2
100
120
140
160
180
D
[t]
V20
40
60
80LO
RC2
C2
2 3 4
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36
DISPLACEMENT [mm]
180
1
80
100
120
140
OAD
[t]
S1 - C2
S1 - RC2
G3 - RC2
G4 - RC2
G5 - RC2
V 020
40
60
0 1 2 3 4 5 6 7 8
G
4/G5
G3
S1
STRAIN []
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TEST RESULTSTEST RESULTS 22NDND PHASEPHASE C2/RC2C2/RC2
200
100
120
140
160
180
D
[t]
20
40
60
80LO
RC2
C2
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36
DISPLACEMENT [mm]
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TEST RESULTSTEST RESULTS 22NDND PHASEPHASE C3/RC3C3/RC3
Specimen C3 was tested up to 80 t.
- The first crack started at a 45 angle from re-entrant corner and up to 65 t it did not
appear others. After that four new major cracks developed, but without significant
.
- The maximum displacement was 5 mm, the remanent was 0.5 mm. Strain gagesattached to the steel reinforcement (S1) indicate 1.95 , which meant that it was at
the yielding level. After that, the specimen was retrofitted and retested.
The specimen RC3 had a linear behaviour up to 90 t, but starting from 64 t it was
observed the composite step by step failure through an inclined crack, which could be
observed also in the load-displacement curve. The curve aspect is very close to the
one of C1 specimen, without significant differences over 100 t.
- The strain gages attached to composite were out of work after 50 t. However,
comparing the maximum strain in steel reinforcements in C3 at 80 t with the same
level in RC3 it could be observed an increase in service load of 25 50 %.
- The maximum load and remanent displacement were identical with the one from C1.The failure was brittle, produced by successive breaking of the carbon fibres along the
principal crack.
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TEST RESULTSTEST RESULTS 22NDND PHASEPHASE C3/RC3C3/RC3
100
120
140
160
D
[t]
20
40
60
80LOA
C3
RC30
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36
DISPLACEMENT [mm]
180-
2
13
100
120
140
160
AD
[t]
S2 - C4
S1 - RC4
S2 - RC4
G3 - RC4
G4 - RC4
G5 - RC4
V 020
40
60
L
G4
G3
G5
S1
0 1 2 3 4 5
STRAIN []
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TEST RESULTSTEST RESULTS 22NDND PHASEPHASE C3/RC3C3/RC3
100
120
140
160
D
[t]
20
40
60
80LOA
C3
RC30
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36
DISPLACEMENT [mm]
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TEST RESULTSTEST RESULTS 22NDND PHASEPHASE C4/RC4C4/RC4
Specimen C4 was tested up to 80 t the first crack started at a 46 angle from re-entrant
corner and up to 60 t it did not appear others.
- After that four new major cracks developed, but without significant openings. The
maximum dis lacement was 5 mm, the remanent was smaller than 0.5 mm.
- Strain gages attached to steel reinforcement (S1) indicated 1.44 , consequently
was at yielding level. After that the specimen was retrofitted and retested.
e spec men a a near e av our up o , w en appeare e rs new
crack. At 119 t a crack developed around the horizontal plates.
- The element failed at 169 t through debonding of vertical plates with an immediate
peeling-off of the horizontal plates. The failure was brittle at the maximumdisplacement of 19 mm, the remament being over 6 mm.
- The maximum measured strain in steel reinforcement was 3.78 at 153 t and 1.44
at 100 t, which indicate an increase of service load by 25 %, compared with the
same strain level of the reference specimen (C2).
- The maximum strain in composite reached 6.72 , which corresponded to 40 % ofthe composites ultimate value.
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TEST RESULTSTEST RESULTS 22NDND PHASEPHASE C4/RC4C4/RC4
100
120
140
160
D
[t]
20
40
60
80LOA
C4
RC4
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36
DISPLACEMENT [mm]
180
2 100
120
140
160
AD
[t]
S1 - C3
S1 - RC3
G3 - RC3
G4 - RC3
G5 - RC3
0
20
40
60
L
G4/G5
G3
S2S1
0 1 2 3 4 5 6 7 8
STRAIN []
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TEST RESULTSTEST RESULTS 22NDND PHASEPHASE C4/RC4C4/RC4
100
120
140
160
D
[t]
20
40
60
80LOA
C4
RC4
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36
DISPLACEMENT [mm]
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TEST RESULTSTEST RESULTS FAILURE MODESFAILURE MODES
V V V
2
13 1 2
3 4
2
13
1
2
43
V V V
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CONCLUSIONSCONCLUSIONS
WITH RESPECT TO THE BASELINE SPECIMEN (C1), THE
MAXIMUM DISPLACEMENT HAD A VERY CLOSE VALUE FOR FABRIC
RETROFITTED ELEMENTS, BUT A DECREASED VALUE, BY MORE
THAN 30%, IN THE CASE OF PLATE RETROFITTED ELEMENTS
18002
13
1200
1500
]
V
12 3 4
900
LOAD[
kN
RC2
RC3
RC4
C1
V
2
13
43
300
1
2
0
0 5 10 15 20 25 30 35
DISPLACEMENT [mm]
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