flexural behavior of strengthened and repaired r.c. beams ... · strengthening and repairing of...

INTERNATIONAL JOURNAL OF CIVIL AND STRUCTURAL ENGINEERING

Volume 3, No 3, 2013

© Copyright by the authors - Licensee IPA- Under Creative Commons license 3.0

Research article ISSN 0976 – 4399

Received on January 2013 Published on March 2013 564

Flexural behavior of strengthened and repaired R.C. beams by using steel

fiber concrete jacket under repeated load Yehia A. Hassanean

1, Kamal Abas Assaf

2, Shehata E. Abdel Raheem

3, Ahmed. N.M. Arafa

4

1- Professor, Civil Engineering Department, Faculty of Engineering, Assiut University, Egypt

2- Associate Prof., Civil Engineering Dept., Faculty of Engineering, Assiut University, Egypt

3- Associate Prof., Taibah University, Madinah, KSA. On leave, Assiut University, Egypt

4- Assistant Lecturer, Faculty of Engineering, Sohag University, Egypt

[email protected]

doi:10.6088/ijcser.201203013052

ABSTRACT

Strengthening and repairing of reinforced concrete beams by using thin fibers concrete jacket

have many advantages such as increasing of ultimate load, enhancement of serviceability

limit state, resistance to fire and avoiding of corrosion problems that appear in steel plate

jacket. The present work conducted to study the strengthening and repairing of reinforced

concrete beams subjected to short time repeated load by using mixed steel fibers concrete

jacket (MSFCJ). For this purpose fourteen reinforced concrete beams have a cross section

120×300 mm, total length 2300 mm were fabricated and tested under three point load. The

used concrete mix contains two mixed shape steel fibers, corrugated and end-hooked steel

fibers. Two of these beams were fabricated without strengthening, the first was tested under

static load up to failure and the second was tested under short time repeated loads up to

failure. The rest twelve beams, six of them were strengthened by U-shape MSFCJ with

various thickness and steel fibers content while the other six beams were loaded up to 0.5 the

ultimate static load and then repaired using MSFCJ. The twelve beams were tested under

short time repeated load. The tests results showed the effectiveness of the proposed technique

in both ultimate and serviceability limit state.

Keywords: Strengthening and repairing, Fiber concrete jacket, High-strength concrete,

mixed steel fiber, Repeated loading.

1. Introduction

The interest of strengthening and repairing of reinforced concrete structures has increased in

the last few years because of poor performance under service loading in the form of excessive

deflections and cracking, construction faults, design faults, excessive deterioration and the

changing in use of structure. In such circumstances, there are various methods for

strengthening and repairing of R.C beams such as externally bonded steel plates, R.C

jacketing and externally bonded fiber reinforced polymer (FRP). All these techniques can be

successfully used but have some limits. In particular, the use of R.C jacket is possible by

adding layers of concrete with thickness larger than 60 – 70 mm due to the presence of rebars

that require a minimum concrete cover (Fatih Altun; 2004). The use of externally glued steel

plates as well as FRP may have problems for fire resistance. Furthermore, the use of these

techniques may not satisfy minimum requirements for serviceability limit states.

During the last 10 years, the use of concrete reinforced with fibers has increased due to its

enhanced flexural, tensile, compressive and fatigue properties. Recently, a new technique has

been developed for strengthening and repairing beams under static loading (Byung Hwan;

Flexural behavior of strengthened and repaired R.C. beams by using steel fiber concrete jacket under

repeated load

Yehia A. Hassanean et al

International Journal of Civil and Structural Engineering 565

Volume 3 Issue 3 2013

1992, Giovanni Martinola et al.; 2007). This solution is based on the application of a thin

jacket in high performance fiber reinforced concrete (HPFRC) with a high compressive

strength and a hardening behavior in tension. This method has more advantages such as

increasing of ultimate load, enhancement of serviceability limit state, resistance to fire and

avoiding of corrosion problems that appear in steel plate jacket. This technique in

strengthening and repairing was undertaken to be the main object of this work by using high

strength concrete with steel fiber. Also all previous investigations conducted on SFC, single

shape of fibers has been used (Johnston and Zemp; 1991, Byung Hwan; 1992, Nasser Abdel

Salam; 2005) and there is no information available on performance of SFC containing fibers

of mixed shape. Therefore the present work was used mixed shape of steel fibers (end hooked,

corrugated) with the understanding that the end hooked fibers are effective in increasing the

ductility whereas, corrugated fibers are effective in increasing the bond between the

components of concrete.

2. Experimental program

2.1 Details of the tested beams

Fourteen reinforced concrete beams with a cross section 120 × 300 mm and total length of

2300 mm were fabricated and tested under three point flexural test. The design of the flexural

and shear steel reinforcement ensured a flexural failure of the beams. The dimension and

details of reinforcement of the tested beams before the application of the proposed

strengthening or repairing techniques are shown in figure 1. Also properties of the tested

beams are given in table 1.Two beams (B0s and B0r) without jacket; B0s was subjected to a

static loading up to failure. Meanwhile B0r was subjected to a short time repeated loading up

to failure. The rest twelve beams, six of them were strengthened by using U-shape of MSFCJ

then divided into two groups (A, B) according to the studied parameters. The other six beams

were loaded up to 0.5 of the ultimate static load of beam B0s (50 KN). Eventually, the beams

were repaired using U-shape of MSFC jacket and divided into two groups (C, D). All

strengthened and repaired beams were subjected to short time repeated loading up to failure.

The details of the tested beams after the application of the proposed technique are shown in

figure 2.

Figure 1: Details of the tested beams


repeated load




Figure 2: Strengthening and repairing scheme and shear connectors details for all

strengthened and repaired beams except BSB2, BRD2 without shear connectors

Table 1: Property of the tested beams

Group

No Parameter

Beam

No

Vf

%

Jacket Thickness Shear

Connector

s

Loading

Type tjb mm tjs (mm

----------

-

-----------------

--

B0s 0.0 0.0 0.0 ------- Static

B0r 0.0 0.0 0.0 ------- Repeated

A

Str

eng

then

ed B

eam

s

Effect of steel

fiber content

BSA1 1 40 30 with Repeated

BSA2 1.5 40 30 with Repeated

BSA3 2 40 30 with Repeated

B

Effect of the

jacket's

thickness

BSB1 1.5 30 30 with Repeated

BSB2 1.5 40 30 without Repeated

BSB3 1.5 50 30 with Repeated

C

Rep

aire

d

Bea

ms Effect of steel

fiber content

BRC1 1 40 30 with Repeated

BRC2 1.5 40 30 with Repeated

BRC3 2 40 30 with Repeated

D

Effect of the

jacket's

thickness

BRD1 1.5 30 30 with Repeated

BRD2 1.5 40 30 without Repeated

BRD3 1.5 50 30 with Repeated

2.2 Materials

The beams were cast with a concrete having a 28 day compressive strength of 27.5 N/mm2

and the constituent materials for 1 m3 are given in Table.2. A normal concrete resistance was

chosen in order to simulate the real case of existing beam and to better highlight the

strengthening and repairing effectiveness. Ordinary Portland cement and local natural sand

were used. The coarse aggregate was gravel with a maximum nominal size of 20 mm. All


repeated load




used materials are match with ECP 203and ACI 215 limits (ACI Committee; 1974, Egyptian

Code of Practice: ECP 203; 2007).

The jacket was caste with a high strength concrete of cubic strength ranged from 82.5 to 93

N/mm2 after 28 days and the constitute materials for 1m3 are given in Table.2. Ordinary

Portland cement and local natural sand were used. The coarse aggregate was crushed basalt

with a maximum nominal size of 10 mm. To enhance the strength of concrete, silica fume

was used. The workability of the mix was improved by using a high–range water reduction

admixture under a commercial name of Sekament R 2004. The concrete mixes incorporated

two different shapes of steel fibers, corrugated and end-hooked steel fibers of size 0.6×2.0×30

mm in ratio 1:1 by weight and have a minimum tensile strength of 400 N/mm2.

The tension reinforcement used was made of 16 mm deformed bars of 430 N/mm2 yield

strength. Deformed bars of 10 mm diameter and 420 N/mm2 yield strength were used as

compression reinforcement. The stirrups used were made of 8 mm smooth bars of 310

N/mm2 yield strength. The used shear connectors were high tensile steel rivets of 520

N/mm2 yield strength have L shape of 50, 20 mm sides and 4 mm diameter and have end

screw with a length 25 mm.

Table 2: Materials for 1 m3 of the used concrete

Type of

Concrete

Cemen

t kg/m3

Silica

Fume

Kg/m3

Sand

kg/m3

Grave

l

kg/m3

Crushed

Basalt

kg/m3

Additive

Litre/m3

Water

Litre/m3

Normal

Strength

Concrete

375 _______ 659 1076 _____ ______ 201

High Strength

Concrete 500 120 450 _____ 1200 17 132

2.3 Strengthening and repairing technique

The external strengthening and repairing system MSFCJ was performed as follows:

1. Preparations of concrete surface by grinding disk then loose particles and dust have

been removed by vacuum cleaner.

2. The bores to accommodate the shear connectors were drilled by using electrical drill.

3. Cleaning the bores by vacuum cleaner in order to have a good bond between the

epoxy and the concrete surface then epoxy resin was placed in the bores. After that,

the shear connectors were inserted into the bores at the indicated position. The

embedded length of shear connectors in concrete was 28 mm and the free length

outside the concrete surface was 22 mm.

4. Just before cast the jacket, the epoxy adhesive was mixed and applied to the concrete

surface to nominal thickness of about 0.5 mm.

5. Cast the MSFC jacket as mentioned before.

The installation process is given in figure 3.


repeated load




2.4 Test procedures and instrumentations

The static and repeated loading of the tested beam were made using testing machine EMS 60

tons. All beams were tested as simple beams with a clear span of 2160 mm using a three

point loading system as shown in Figure 1. In static tests; the load was applied in increments

of 5 KN. In repeated tests, the fatigue loading was applied as stationary pulsating

concentrated load at the mid-span of the beam. The applied minimum load was constant at 14

KN (weight of steel tar of testing machine). The maximum load level was taken 0.95 of the

ultimate load of the reference beam tested statically (B0s). The frequency was chosen to be

500 cycles per minute and the chosen stroke was 0.5 mm, the loading scheme is shown in

Figure 4. For all tested beams, mid-span deflection, strain at the center of the main

reinforcement, strain in the compression zone of concrete surface at mid span section, first

crack load, and failure load were measured. Also, crack patterns and failure mode were

observed carefully.

Figure 3: Strengthening and repairing technique:

(a) exposed aggregate after grinding disk of concrete; (b) shear connectors after inserting into

their bores; (c) priming surface process; (d) cast the jacket; (e) beam after cast the jacket

Figure 4: Sketch of sequence of loading versus deflection (repeated tests)


repeated load




3. Test results and discussion

The data in table 3 includes the cracking loads, the number of cycles to failure, maximum

deflections and strains. It also contains the failure mechanisms for the tested beams.

3.1 Pattern of crack and failure mechanism

For beam B0s which was subjected to static loading, the first crack was observed under point

of load application at section of maximum bending moment. With further increase in the

applied load, further flexural cracks are appeared and extended vertically upwards with the

development of new cracks between the earlier cracks. At the last stages of loading, the

cracks in the mid span zone continue to propagate vertically and few cracks developed in

between, while more cracks form in the shear span, then trended to progress towards the load

point diagonally (flexural-shear cracks) finally the beam failed by widening in the flexural

cracks accompanied by crushing of the concrete at the top compression side under the point

of load application. For "B0r" which tested under repeated load, the cracks are propagated in

the same manner of beam B0s up to the end of the static loading. When the beam is subjected

to the repeated loading the number and width of the cracks are increased dramatically. The

mode of failure as the same as "B0s", but the cracking pattern due to repeated loading was

more extensive.

Table 3: Results of tested beams

Bea

m N

o

Vf

%

tjb

mm

Concrete Strengths

for the jacket

( kg/cm2) Loading

type

Pcr

(KN)

N

×100

Deformations

Mo

de

of

fail

ure

fcu fct fr δcr

(mm)

δu

(mm)

εsu

×10-6

εcu

×10-6

B0s 0 0 ------ ----- ----- Static 20 195 2330 41 2.1 ــــــــــ F.C

B0r 0 0 ----- ----- ----- Repeated 20 25 2.36 45 2450 226 F.C

BSA1 1 40 825 56 75 Repeated 25 50 1.53 59.3 1850 197 F.C

BSA2 1.5 40 900 76 109 Repeated 28 90 1.04 53 1690 322 F.C

BSA3 2 40 930 80 115 Repeated 32 110 0.65 63.1 1250 174 F.C

BSB1 1.5 30 900 76 109 Repeated 25 55 0.97 49.23 1690 315 F.C

BSB2 1.5 40 900 76 109 Repeated 29 75 0.85 53.8 1205 280 F.C

BSB3 1.5 50 900 76 109 Repeated 35 130 0.7 42 1800 288 F.C

BRC1 1 40 825 56 75 Repeated 23 40 1.47 57.1 2009 291 F.C

BRC2 1.5 40 900 76 109 Repeated 27 75 1.76 48.4 1900 295 F.C

BRC3 2 40 930 80 115 Repeated 30 90 1.25 51.14 1495 320 F.C

BRD1 1.5 30 900 76 109 Repeated 25 45 1.83 46 2200 360 F.C

BRD2 1.5 40 900 76 109 Repeated 27 60 1.44 62 2442 250 F.B

BRD3 1.5 50 900 76 109 Repeated 33 100 1.39 65 2129 360 F.C


repeated load




For the strengthened and repaired beams, it was observed that the strengthening and repairing

with MSFCJ decreased the number of cracks and all cracks concentrated in the middle third

of the tested beams in comparison the reference beam B0r. With increasing the steel fiber

content, more cracks with smaller width was observed. This was because the steel fibers

across cracks contributed in increasing the ductility of the tested beams and reducing the

stress in the tensile steel reinforcement. All mode of failure for the strengthened or repaired

beams was flexural accompanied by crushing of the concrete at the top compression side

under the point of load application except the repaired beam BRD2 suffered from the

debonding of the jacket at the last stage of loading. Meanwhile the identical strengthened

beam BSB2 failed without deponding. This may be reasonable for the absence of shear

connectors as well as the initial cracks existing in the cracked beam BRD2. Figure 5 shows

the cracking pattern and failure mechanisms for some tested beams.

Figure 5: Crack pattern and mode of failure for some tested beams


repeated load




3.2 Fatigue life of the tested beams

The maximum number of cycles for the tested beams is presented in table 3. Generally, the

number of cycles for strengthened and repaired beams is larger than the reference beam; the

rate and value of increasing depend on the fiber content, jacket thickness and the interface

strength.

Figures 6 and 7 show a comparison between the reference beam and the strengthened or

repaired beams with a 40 mm jacket thickness and variable steel fiber content 1%, 1.5% and

2%. The increasing was 100%, 260% and 340% respectively for the strengthened beams with

respect to the reference beam. Meanwhile the increasing was 60%, 200% and 260%

respectively for the repaired beams. Also, it is clear from these figures that adding 1.5% fiber

content to the concrete used in jacket has a significant effect in increasing the maximum

number of cycles for the strengthened and repaired beams.

Figures 8 and 9 compare the maximum number of cycles for the reference beam and each of

strengthened or repaired beams with a 1.5% fiber content and variable jacket thickness 30, 40

and 50 mm jacket thickness. It can be noticed from these figures that the increase of jacket

thickness has a dramatic effect in increasing the number of cycles for the tested beams. The

enhancements were 120%, 260% and 420% respectively for the strengthened beams. At the

same time the enhancements were 80%, 200% and 300% respectively for the repaired beams.

20

40

60

80

100

120

Steel Fiber Content %

Ma

xim

um

Nu

mb

er o

f C

ycl

es x

10

0

0.0 1.0% 2.0 3.00.0 1.5% 2%

20

40

60

80

100

Steel Fiber Content %

Ma

xim

um

Nu

mb

er o

f C

ycl

es x

10

0

0.0 1.0% 1.5% 2%

Figure 6: Effect of fiber content on

maximum number of cycles for strengthened

beams.

Figure 7: Effect of steel fiber content on

maximum number of cycles for repaired

beams.

20

40

60

80

100

120

140

Jacket Thickness (mm)

Ma

xim

um

Nu

mb

er o

f C

ycl

es x

10

0

0.0 30 40 50

20

40

60

80

100

120

Jacket Thickness (mm)

Ma

xim

um

Nu

mb

er o

f C

ycl

es x

10

0

0.0 30 40 50

Figure 8: Effect of jacket thickness on

maximum number of cycles for strengthened

beams.


maximum number of cycles for repaired

beams.

Beam without Shear

Connectors Beam without Shear

Connectors


repeated load




Investigating figures 10 and 11, it can be observed that the absence of shear connectors lead

to decreasing the maximum number of cycles and preventing the strengthened or repaired

beams to reach its predicted maximum number of cycles. This may be reasonable for the

separation of the jacket from the main beam especially at the last stages of loading.

10

20

30

40

50

60

70

80

90

100

Maxim

um

Num

ber o

f Cycle

s x 1

0

Reference

Beams

Beam with Shear

Connectors

Beam without

Shear Connectors 20

30

40

50

60

70

80

Maxim

um

Num

ber

of C

ycl

es x

10

2

Reference

Beams

Beam with Shear

Connectors

Beam without

Shear Connectors

Figure 10: Interface effect on maximum

number of cycles for strengthened beams.

Figure 11: Interface effects on maximum

number of cycles for repaired beams.

3.3 Deformation response

3.3.1 Deflection

The changes of the mid-span deflections with the increase of the number of cycles for all

beams tested under short time repeated loading are given in figures 12 to 15. It can be

observed that in all beams there was an initial increase of the mid-span deflection, followed

by a stable region where the deflection remained relatively constant through many number of

cycles followed by a dramatic increase of deflection just before failure. Also, it can be

observed that with increasing the fatigue life of the tested beams, the deflections increases

significantly. A greater number of cracks resulting from cycling may cause this.

For the strengthened or repaired beams with a constant jacket thickness and variable steel

fiber content 1%, 1.5% and 2%, it is clear that at the same number of cycles, the mid-span

deflection decreases as the fiber content increases. For strengthened beams, the increasing of

steel fiber from 1% to 1.5% decreased the deflection by 58% at 5000 cycle while at the same

number of cycles the decreasing was 70% when the steel fiber increased from 1% to 2% as

shown in figure 16. For repaired beams, the Increasing of steel fiber content from 1% to 1.5%

decreased the mid-span deflection by 41% at 4000 cycle. Meanwhile at the same number of

cycles, the increasing of steel fiber content from 1% to 2% decreased the mid-span deflection

by 63% as shown in figure 17. It is clear that the slope of line from 1% to 1.5% is larger than

the slope of line from 1.5% to 2%.

For the beams that were strengthened or repaired by MSFC jacket with a constant steel fiber

content and variable jacket thickness, it is obvious that at the same number of cycles,

increasing the jacket thickness causes a significant decreasing in the mid-span deflection. For

example, the increasing of jacket thickness for strengthened beams from 30 mm to 40 mm

decreased the deflection by 44% at 5500 cycle while at the same number of cycles the

increasing of jacket thickness from 30 mm to 50 mm decreased the deflection by 62% as

shown in figure 18. For repaired beams, the increasing jacket thickness from 30 mm to 40

mm decreased the mid-span deflection by 28% at 4500 cycle. Meanwhile at the same number

of cycles, the increasing of jacket thickness from 30 mm to 50 mm decreased the mid-span


repeated load




deflection by 39% as shown in figure 19. Figures 20 and 21 show the effect of shear

connectors between the main beam and the jacket. The absences of the shear connectors

decreased the effectiveness for each strengthened beams and repaired beams.

0

10

20

30

40

50

60

70

0 10 20 30 40 50 60 70 80 90 100 110 120 130

Number of Cycles x102

Def

lect

ion

(m

m)

B0r - Reference BeamBSA1 - 1 % FiberBSA2 - 1.5 % BSA3 - 2 %

0

10

20

30

40

50

60

0 10 20 30 40 50 60 70 80 90 100 110 120 130

Number of Cyclesx102

De

fle

cti

on

(m

m)

B0r - Reference Beam

BSB1 - 3 cm Jacket Thickness BSB2 - 4 cm

BSB3 - 5 cm


variation of mid span deflection with

number of cycles for strengthened beams


variation of mid span deflection with number

of cycles for strengthened beams

0

10

20

30

40

50

60

0 10 20 30 40 50 60 70 80 90

Number of Cycles x 102

De

fle

cti

on

(m

m)


BRC1 - 1 % Fiber

BRC2 - 1.5 % BRC3 - 2 %

0

10

20

30

40

50

60

70

0 10 20 30 40 50 60 70 80 90 100


Def

lect

ion

(m

m)


BRD1 - 3 cm Jacket Thickness

BRD2 - 4 cm

BRD3 - 5 cm


variation of mid span deflection with

number of cycles for repaired beams


variation of mid span deflection with number

of cycles for repaired beams.

10

20

30

40

50

60

1 1.5 2Steel Fiber Content

Defl

ecti

on

(m

m)

20

30

40

50

60


Defl

ecti

on

(m

m)


mid-span deflection of strengthened beams

after 5000 cycles


mid-span deflection of repaired beams after

4000 cycles


repeated load




10

20

30

40

50

30 40 50Jacket Thickness (mm)

Def

lecti

on

(m

m)

20

30

40

50

30 40 50

Jacket Thickness(mm)

Defl

ecti

on

(m

m)

Figure 18: Jacket thickness effect on mid-

span deflection of strengthened beams after

5500 cycles

Figure 19: Effect of jacket thickness on mid-

span deflection of repaired beams after 4500

cycles

10

15

20

25

30

35

40

45

50

Defl

ecti

on (m

m)

Reference

Beams

Beam with Shear

Connectors

Beam without

Shear Connectors

20

25

30

35

40

45

50

Deflection (m

m)

Reference

Beams

Beam with Shear

Connectors

Beam without

Shear Connectors

Figure 20: Effect of interface strength on

mid-span deflection of strengthened beams

after 2500 cycles

Figure 21: Effect of jacket thickness on mid-

span deflection of repaired beams after 2500

cycles

3.3.1 Strain response

The recorded strains on the main steel reinforcement and concrete (top surface) for the

strengthened and repaired beams are given in Figures 22 to 29. In both beams, the strain in

main steel increased suddenly before failure, indicating yielding of the reinforcement. At that

point, strain in the concrete increased but remained lower than strains corresponding to

expected ultimate behavior (0.003 micro-strain). It can be also seen that there is a more

gradual increase in the steel and concrete strain as the beam approaches its fatigue life. This

may be due to increasing the deflection resulting from increased cycling

Figures 30 to 33 show a comparison between the strains in main steel and concrete for those

beams which were strengthened or repaired by 40 mm jacket thickness and variable steel

fiber content. It is clear that at the same number of cycles, the strains decrease as the steel

fiber content increases. It can also be observed that the increasing of steel fiber content from

1% to 1.5% has a significant decreasing in the strains in both main steel and concrete.

Figures 34 to 37 show the effect of jacket thickness in strains for strengthened and repaired

beams. It can be observed that at the same number of cycles, the strains decrease as the jacket

thickness increases. From the same figures, it is clear that the absences of the shear

connectors increased the strains for the strengthened and repaired beams.

Beam without Shear

Connectors

Beam without Shear

Connectors


repeated load




0

500

1000

1500

2000

2500

0 10 20 30 40 50 60 70 80 90 100 110


Ma

in S

teel

Str

ain

(M

icro

str

ain

)


BSA1 - 1 % Fiber

BSA2 - 1.5 %

BSA3 - 2 %

0

500

1000

1500

2000

2500

0 10 20 30 40 50 60 70 80 90 100 110 120 130


Ma

in S

teel

Str

ain

(M

icro

Str

ain

) B0r - Reference Beam

BSB1 - 3 cm Jacket Thickness BSB2 - 4 cm

BSB3 - 5 cm


variation of strain in main steel with number





0

500

1000

1500

2000

2500

0 10 20 30 40 50 60 70 80 90


Ma

in S

teel

Str

ain

(M

icro

Str

ain

)


BRC1 - 1 % Fiber

BRC2 - 1.5 %

BRC3 - 2 %

0

500

1000

1500

2000

2500

0 10 20 30 40 50 60 70 80 90 100


Ma

in S

teel

Str

ain

(M

icro

Str

ain

)



BRD2 - 4 cm

BRD3 - 5 cm



of cycles for repaired beams




0

100

200

300

400

0 10 20 30 40 50 60 70 80 90 100 110

Cycles x 102

Co

nc

rete

str

ain

(M

icro

Str

ain

)


BSA1 - 1 % Fiber

BSA2 - 1.5 %

BSA3 - 2 %

0

100

200

300

400

0 10 20 30 40 50 60 70 80 90 100 110 120 130

Cycles x 102

Co

nc

rete

str

ain

(M

icro

Str

ain

)


BSB1 - 3 cm Jacket Thickness

BSB2 - 4 cm

BSB3 - 5 cm


variation of strain in concrete with number



variation of strain in concrete with number of

cycles for strengthened beams


repeated load




0

100

200

300

400

0 10 20 30 40 50 60 70 80 90


Co

nc

rete

str

ain

(M

icro

Str

ain

)

B0r - Reference BeamBRC1 - 1 % FiberBRC2 - 1.5 % BRC3 - 2 %

0

100

200

300

400

0 10 20 30 40 50 60 70 80 90 100

Number Cycles x 102

Co

nc

rete

str

ain

(M

icro

Str

ain

)



BRD2 - 4 cm

BRD3 - 5 cm


variation of strain in concrete with number



variation of strain in concrete with number of

cycles for repaired beams

500

1000

1500

2000


Ma

in S

teel

Str

ain

(M

icro

stra

in)

500

1000

1500

2000


Ma

in S

tee

l S

tra

in (

Mic

ro

stra

in)


main steel strain for strengthened beams

after 5000 cycles


main steel strain for repaired beams after

4000 cycles

50

100

150

200


Co

ncrete

Str

ain

(M

icro

stra

in)

100

150

200

250

300


Co

ncr

ete

Str

ain

(M

icro

stra

in)


concrete strain for strengthened beams after

5000 cycles


concrete strain for repaired beams after 4000

cycles


repeated load




0

500

1000

1500

2000

30 40 50Jacket Thickness(mm)

Ma

in S

teel

Str

ain

(M

icro

stra

in)

500

1000

1500

2000

2500


Main

Ste

el S

train

(M

icro

stra

in)


main steel strain for strengthened beams

after 5500 cycles

Figure 35: Effect of jacket thickness on main

steel strain for repaired beams after 4500

cycles

50

100

150

200

250

300

350


Co

ncrete

Str

ain

x 1

0-6

100

150

200

250

300

350

400


Con

cret

e S

train

(M

icro

stari

n)


concrete strain for strengthened beams after

5500 cycles


concrete strain for repaired beams after 4500

cycles

4. Conclusions

Based on the test results and discussions above, the following conclusions can be drawn.

1. The strengthening and repairing with MSFC jacket decreased the number of cracks

and they were concentrated in the middle third avoiding the forming of shear cracks.

2. Presences of shear connectors in the jacket play a role in enhancing the bonding

between the main beam and the jacket and prevent the debonding failure. While the

absence of shear connectors lead to prevent the strengthened and repaired beams to

reach its predicted maximum number of cycles.

3. The application of MSFC jacket on a R.C beam provides a significant increase in the

strengthened and repaired beams stiffness.

4. The application of MSFC jacket on a R.C. beam provides an increase of the maximum

number of cycles from 2 to 5 times for strengthened beams and from 1.6 to 4 times for

repaired beams depending on the fiber content, jacket thickness and the interface

strength.

5. Adding 1.5% fiber content to the concrete used in the jacket has a significant effect in

increasing the number of cycles and decreasing both the deflections and strains. This

content may be the economic steel fiber content that can be added.

Beam without Shear

Connectors Beam without Shear

Connectors

Beam without Shear

Connectors

Beam without Shear

Connectors


repeated load




6. The proposed technique provides a significant structural enhancement at the

serviceability limit state; due to the remarkably increase of the beam stiffness and

decrease the measured deformations.

5. References

1. ACI Committee 215, (1974), Consideration for Design of Concrete Structures

Subjected to Fatigue Loading, ACI Journal, 71(3), pp 97-121.

2. Byung Hwan, (1992), Flexural Analysis of Reinforced Concrete Beams Containing

Steel Fibers, Journal of Structural Engineering, 118(10), pp 2821-2836.

3. Egyptian Code of Practice: ECP 203-2007, (2007), Design and Construction for

Reinforced Concrete Structures, Ministry of Building Construction, Research Center for

Housing, Building and Physical Planning, Cairo, Egypt.

4. Fatih Altun, (2994), An Experimental Study of the Jacketed Reinforced Concrete

Beams under Bending, Construction and Building Materials, 18, pp 611-618.

5. Giovanni Martinola, Alberto Meda, Giovanni A. Plizzari and Zila Rinaldi, (2007),

Strengthening and Repairing of RC Beams with Fiber Reinforced Concrete, Cement،

Concrete Composites, 32, pp 731-739.

6. Johnston, C.D., Zemp, R.W., (1991), Flexural Fatigue Performance of Steel Fiber

Reinforced Concrete Influence of Fiber Content, Aspect Ratio and Type, ACI Materials

Journal, 88(4), pp 374-383.

7. Nasser Abdel Salam, (2005), Repair and Strengthening of Reinforced Concrete Beams

Using Fiber Reinforced Concrete, M.Sc. Thesis, Zagazig university, Egypt.

flexural behavior of strengthened and repaired r.c. beams ... · strengthening and repairing of...

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