05 Research Dapped-Ends Nagy-Gyorgy T

8/11/2019 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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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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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

-

- 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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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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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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.- 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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200


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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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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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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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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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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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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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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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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THANK YOUTHANK YOU

FOR YOUR KINDFOR YOUR KIND

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05 Research Dapped-Ends Nagy-Gyorgy T

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