Paper2

1

CONCRETE-COMPOSITE BEAM-COLUMN JOINTS-

2

II. PERFORMANCE OF FRPC REHABILITATED SPECIMENS

3

A. Mukherjeea *, G. L. Raib a

4

Director, Thapar University,

5

Patiala 147004, India

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Tel: +91 175 2393001, 2363007 Fax: +91 175 2364498, 2393005

7

b

Research scholar, Department of Civil Engineering, Indian Institute of Technology

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Bombay, Mumbai 400076, India

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Tel: +91 9322597149, +91 22 32610117

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E-mail: a [email protected], b [email protected]

11

ABSTRACT

12The present paper discusses the performance of reinforced concrete (RC) beam-column 13joints under cyclic excitation. Beam-column joints with two types of reinforcement 14detailing, ductile and brittle, have been cast. The joints are subjected to cyclic loading of 15monotonically increasing amplitude until failure. Post failure, the joints have been 16rehabilitated using fiber reinforced polymer composites (FRPC). The rehabbed joints 17have been subjected to the same load regime. The performance of rehabbed joints has 18been compared with that of the fresh joints. The investigation highlights the efficiency of 19the proposed rehabilitation scheme in enhancement of strength and ductility of the joints. 20In this part of the paper, the performance of the rehabbed joints has been discussed. 21Keywords : Reinforced concrete, Beam-column Joints, Fiber Reinforced Polymer 22Concrete (FRPC), Rehabilitation, Ductility, energy dissipation.

1

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1 2

INTRODUCTION

3Rehabilitation and retrofits of reinforced concrete framed structures is of immense 4concern of present construction community. The typical lacunas in the existing structures 5are improper detailing of reinforcements at the joints that lead to their brittle failure. The 6use of reinforced concrete jackets [1] and steel plate jackets [2] to strengthen the joints 7has been reported earlier. However, execution of such rehabilitation is disruptive to the 8operation of the facility, labor intensive and very time consuming. The fiber reinforced 9polymer composites (FRPC) have promise in alleviating these difficulties. The efficiency 10of FRPC as a device for enhancement of bending and shear capacities of flexure elements 11[3] and enhancement of confinement of concrete in compression elements [4] has been 12well established. 13Some apprehensions have been expressed on the efficiency of FRPC in mitigating such 14distresses because of the difficulty in maintenance of continuity of the fibers at the joints. 15In extreme load conditions, such as earthquakes, the ductility of the joint to dissipate the 16energy is paramount. The brittleness of FRPC is also considered a negative. However, 17there is near unanimity among academic community regarding the efficacy of FRPC in 18rectifying these deficiencies. The lack of ductility of a joint with inadequately lapped 19steel reinforcements has been mitigated by a hybrid of carbon fiber reinforced polymer 20(CFRP) sheets and steel angles and bolts [5]. Improvement of the flexure capacity of the 21joints has been reported [6-7] by glass, Kevlar and carbon composites. The shear 22deficient frames have been strengthened by adhesively bonding CFRP strips and sheets 23on the external surfaces of flexure members [8] and a design methodology for such joints

1

2

1[9] has been proposed. Effect of CFRP wraps on enhancement of shear capacity of RC T2joints [10] has been reported. Numerical models to predict the load-deflection behavior of 3RC joints have also been proposed [11]. The combined shear deficiency and bond slip 4has been treated by a hybrid of steel anchors and CFRP sheets [12-13]. 5In précis, success has been reported by various researchers on rectifying the deficiencies 6in RC beam-column joints before they are damaged with a multitude of techniques. 7However, in many cases the structures need to be rehabilitated after they have been 8damaged. Mukherjee and Joshi [7] reported pilot tests on damaged concrete joints that 9have been restored with FRPC after the original joint had failed. A complete recovery of 10strength and ductility of the joint was observed through restoration of damaged concrete 11and application of FRPC on the affected surface. 12In this paper, we report a series of tests on beam-column specimens of representative 13size. A number of concrete beam-column joints have been cast and they have been 14subjected to a cyclic load regime of increasing amplitude until their resistance has been 15completely consumed. The joints are repaired by restoring the concrete sections. The 16tensile reinforcements and the confinement of the concrete have been augmented using 17CFRP strips and sheets. The rehabilitation technique is based on the following principles: 18

-

19 20 21

1

The rehabbed specimens must achieve at least the same peak strength and peak deformation as in the fresh joint.

-

The rehabilitation should be fast, clean and least intrusive requiring no replacement of damaged parts.

3

1

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The technique must be amenable to site adaptation.

2

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The repair must be durable. Therefore, use of metal has been avoided to

3 4

circumvent durability problems of a hybrid system. -

5 6 7

The mechanics of the rehabilitated joint should be understood to enable development of analytical models and design methodologies.

-

The method should be able to rectify permanent deformations, if any, that the initial damage might have caused.

8The rehabilitated joints and the fresh joints have been subjected to the same load cycles 9until failure. The performance of the rehabilitated joints vis-à-vis the fresh joints has been 10reported. 11

MATERIAL SYSTEM

12The CFRP was used in two forms- carbon plates (CP) and carbon sheets (CS). The plates 13have been used as longitudinal reinforcements at the time of rehabilitation of the joints. 14They are precured unidirectional fiber composites of 50mm width. They have one surface 15roughened for adhesive bonding with concrete. At the time of application the resin is 16applied on the rough surface only and the resin does not ooze through the fibers. 17Therefore, their fiber volume fraction and dimensions remain unchanged. Hence, their 18mechanical properties have been defined as that of the composite. 19The sheets, on the other hand, are used as transverse reinforcement at the time of 20rehabilitation by wrapping them around the beams and column sections. They need to be 21flexible and therefore, are uncured. The resin oozes through them at the time of 22application. As a result, it is not possible to maintain an accurate volume fraction or 1

4

1dimensional accuracy. Therefore, in the case of the sheets the neat fiber properties have 2been reported in Table 1 and the mechanical strength of the resin is ignored. 3

REHABILITATION OF SPECIMENS

4The specimens described in Paper I have been used here for rehabilitation. It may be 5noted that the beam-column joint specimens were subjected to a cyclic displacement 6regime and they had no residual strength after the test. These specimens have been 7rehabilitated using CFRP. The main shortcomings and damages in those samples were 8the following: 9

•

Two sets of specimens, ductile and brittle, were designed. While the ductile

10

specimens had closely spaced links in the beam, column and the joint core the

11

brittle specimens had large spacings between links. The specimens failed in brittle

12

fashion in shear and bulging. The lack of confinement and shear capacity of the

13

joints was compensated by CS wraps on both beams and columns.

14

•

Concrete had spalled extensively in beams, columns and joint core of all the

15

specimens. The sections were rebuilt using fresh concrete. An epoxy mortar and

16

low viscosity grout was used in the less severely affected areas.

17

•

The longitudinal reinforcements in beams had yielded and in some cases ruptured.

18

There was loss of bond between the concrete and the reinforcements. No

19

additional steel reinforcement was provided to compensate for the yielded and

20

broken reinforcement. The tensile capacity of the section was revived using FRPC

21

only. CP was used on both faces of the beam to compensate for the lost

22

reinforcement.

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5

1Prior to the application of FRPC the damaged specimens were rebuilt using the following 2steps: 3

•

Loose concrete was removed and the surfaces were cleaned of dirt.

4

•

In the areas where almost entire section was lost the section was rebuilt with

5

concrete. A formwork was placed in the affected region and a free flowing

6

concrete was poured for filling the voids.

7

•

The fresh concrete was cured as usual.

8

•

The area where there were large cracks but the concrete did not spall totally an

9

epoxy mortar (one part epoxy with 5 parts quartz sand) was used to rebuild the

10 11

lost concrete. •

12 13

Cracks of less than 1mm width was filled with an epoxy resin of viscosity 100cps by pressure grouting.

•

14

Concrete surface where the FRPC has been overlaid was smoothed by removing sharp protrusions. A thixotropic epoxy filler was used in filling small dents.

15

•

The corners are rounded off to a radius of 15 mm.

16

•

The surfaces were cleaned using cloth and then acetone was applied.

17 FRPC has been applied in Various Steps: 18Step1: CP Attachment on Beam 19CPs have been used on the top and bottom surfaces of the beams as tensile 20reinforcements. To anchor the CP at the joint an incision of 5mm thickness and 60mm 21width has been made in the column at the beam-column interface. A special cutting 22equipment was fabricated to make the groove (Fig. 1a). The equipment could cut through 23the entire depth of the column. However, keeping in mind that there could be practical

1

6

1difficulties in making a through incision the effect of a partial incision was also studied. 2The groove is filled up with the adhesive and the CP is inserted into the groove. The 3epoxy was allowed to cure to obtain an end anchor. 4In this investigation, some of the CPs have been prestressed for remediation of permanent 5settlements and the misalignment of the joints as a result of damage infliction. For 6application of prestress a special device has been fabricated (Fig. 1b). In this device there 7are two components. One is attached to the structure and the other grips the free end of 8the CP. Using a screw jack between the two parts the CP is pulled to the desired tension. 9The groove at the other end of the CP must be designed to withstand this pull. After the 10desired correction in the alignment is achieved, the CP was adhesively bonded to the 11surface of the beam and allowed to cure. After the epoxy has completely cured the 12presterssing device was released and the force transfer between the CP and the concrete 13beam was through the epoxy (Fig. 1c). Both top and bottom faces of the beam had CPs 14attached to them (Fig. 2a). 15Step 2: CS Attachment 16CS was used for the rest of the rehabilitation. CS was adhesively bonded to the two faces 17of the column and the beam that did not have a beam attached (Fig.2b). The direction of 18the fiber was along the axis of the elements. 19Step 3: Wrapping Beam and Column with CS 20The beam and the column were wrapped with CS (Fig. 2c). Fig. 1d shows the photograph 21of a specimen after the complete rehabilitation. 22The experimental setup and procedure described in paper I have been followed in the 23testing of the rehabbed specimens as well.

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1 2

EXPERIMENTAL RESULTS

3The damage process in the case of rehabbed specimens was less visual due to the CS 4wrap on the potential damage zone. The wrapped specimens did not show any damage 5until an advanced stage of deformation. A crack across the depth of the beam at the face 6of the column had appeared and increased in width along with the increase in the 7deformation. A small quantity of fine cement powder escaped from the crack at each 8epoch of deformation. After the termination of the loading the CS wraps were removed 9and the condition of the concrete was examined for damages. This will be discussed later. 10The load-deflection hysteresis plots for both the arms of all the specimens have been 11presented in Fig. 3. These graphs may be compared with the plots in paper I to evaluate 12the performance of the rehabbed joints. Although it is clear from the hysteresis graphs 13that both the peak load and the peak deformation have increased in the rehabbed 14specimens it is difficult to compare the graphs. To maintain clarity we shall compare the 15envelope graphs that are derived from the hysteresis plots. 16 Original vs Rehabbed 17The envelope graphs of the fresh and rehabbed specimens have been presented in Fig. 4. 18It is clear that both the ductile and brittle specimens had gained in strength and ductility 19through the rehab. The rapid loss of stiffness in the brittle specimens could be avoided 20totally. The rehabbed brittle specimen had much higher peak load and deformation than 21the fresh ductile specimen. This demonstrates that deficient joints can be effectively 22rehabbed by the proposed technique. The energy dissipation graphs for the fresh and 23rehabbed specimens, both brittle and ductile, have been presented in Fig. 5.

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1The performance of the rehabbed specimens vis-à-vis the fresh specimens is presented in 2Table 3. There is improvement in both yield and peak loads and final displacements in 3rehabbed specimens. The energy dissipation of the rehabbed specimens is far higher than 4that in the fresh specimens. The rehabbed brittle specimens had higher energy dissipation 5than even the fresh ductile specimens. Hence, it can be concluded that the proposed 6rehabilitation technique can remedy all the deficiencies in the brittle specimens. 7 8 Anchorage Length 9Two types of anchorages, total and partial, have been studied. Fig. 6 presents the 10envelope curves of both ductile and brittle specimens. Both types of anchorages have 11surpassed the performance of the fresh specimens. Although the preyield behavior of the 12specimens have been very similar the postyield trend of the totally anchored specimens 13has been far superior than that of the partially anchored specimens. In a few cases a 14significant bond slip was found in the partially anchored specimens (Fig 6b, positive 15side). Understandably, there was a rapid loss of stiffness in the case of bond slip. None 16of the totally inserted specimens had any loss of bond. As a result of the superior 17postyield behavior the energy dissipation of the totally inserted specimens was much 18higher than the rest of the specimens (Table 3). 19Level of Prestress 20It has been mentioned earlier that the permanent deformations in the damaged joints have 21been rectified by prestressing the CPs. Only brittle specimens have been rehabbed with 22prestressing. The effect of prestressing on the cyclic loading performance of the joints has 23been investigated here. The envelope curves of the prestressed specimens and ordinary

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1specimens have been presented in Fig. 7. Prestressing has extended the linear portion of 2the envelope. This shows that the initiation of damage has been delayed by prestressing. 3However, the postyield behavior of the prestressed joints was more uncertain. In the 4present case the reinforcing bars in one of the beams of both the prestressed specimens 5had fractured. There was a loud sound before the failure of the specimens. The bar 6breakage resulted in a sudden change in the force applied by the dynamic actuators. In the 7case of partially inserted specimen this triggered the safety mechanism and the actuator 8stalled (Fig. 7b). Although the instrument recorded the hysteresis even after the breakage 9of the bar in case of the totally inserted specimen a rapid loss of stiffness was observed. 10Although a direct link between the prestressing and bar breakage could not be 11established, it can be concluded that the prestressing had an adverse effect on the 12postyield behavior of the specimens and ductility was sacrificed. The energy dissipation 13calculations had to be carried out on the truncated data (Fig. 8). The energy dissipation of 14the specimen rehabbed with prestressing exceeded that of the fresh specimens. However, 15there was a marked reduction in the energy dissipation in the prestressed specimens in 16comparison to the non-prestressed specimens. This point requires further investigation 17before a safe level of prestressing could be established. 18Performance of Arm 2 19It has been mentioned earlier that specimens had two arms. The arms have been subjected 20to cyclic loading sequentially. So far the results of the first arm have been presented. The 21second arm was tested after testing the first arm to have an assessment of the 22performance of the severely damaged joints. Figure 9 presents the envelope of the fresh 23and the rehabbed specimens. Four rehabbed specimens were tested- two with total

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1incision and the other two with partial incision. One each of the specimens of each group 2was prestresssed. 3The specimens with total incision surpassed the fresh specimens in both the peak load 4and ultimate displacement. Understandably, the energy dissipation in the rehabbed 5specimens was far greater than that in the fresh specimens (Table 3). The prestressed 6specimen demonstrated higher peak load but lower ultimate displacement than the plain 7specimen. This is consistent with the observations in Arm 1. 8The partially anchored specimens exhibited much lower stiffness than all other specimens 9right from the beginning of loading. It may be noted that in both these specimens the 10main reinforcements had fractured during the testing of Arm 1. Therefore, they 11experienced bond slip resulting in lower stiffness. At higher loads, instead of softening, 12these specimens exhibited a tendency of hardening. This also indicates bond slip and the 13hardening occurs due to friction that occurs at larger displacement levels. Albeit lower 14stiffness the specimens with partial incision had much higher energy dissipation than the 15fresh specimen (Table 3). 16Failure Modes 17Unlike the fresh specimens the progression of damage in the rehabbed specimens was not 18visible, except occasional discoloration of the adhesive, due to the CS wrapping on the 19specimens. The wrapping was cut open after the tests to observe the failure mode (Fig. 2010). The shear cracks that occurred in the fresh specimens were absent in the rehabbed 21ones. The spalling and subsequent formation of hinge did not occur in the rehabbed 22specimens. Hence, it can be concluded that the wrapping was able to avoid both modes of 23brittle failures- shear and loss of confinement; the two most common occurrences in the

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1structures that suffer an earthquake (Fig. 1, Paper I). The damage in the rehabbed 2specimens was due to wide cracks at the column faces. Clearly, this is a bending failure 3and therefore, the rehabbed joints exhibited ductility and higher energy dissipation. 4 5

CONCLUSIONS AND RECOMMENDATIONS •

The rehabilitation technique proposed in the present paper has been very effective

6

and it has restored the strength and ductility of severely damaged beam-column

7

joints.

8

•

9 10

higher peak load and deflection in comparison to the joints with ductile detailing. •

11 12

The joints that were originally brittle could be rehabbed and those joints had

The yielded longitudinal steel reinforcements in the flexure members have been compensated for with carbon plates.

•

The lack of confinement and shear capacity of the joints lead to brittle failure. The

13

carbon fiber sheets wrapped around the members dramatically improves the

14

ductility and energy absorption of the joint.

15

•

Anchoring of CPs in the joint is paramount for achieving their superior

16

performance. Although there is very little difference in the preyield behavior

17

between the partially anchored and the fully anchored joints the fully anchored

18

joints exhibited far superior postyield behavior.

19

•

20 21

The permanent deformations in a damaged joint may be rectified by application of prestress on the CPs.

•

The joints with prestressed CPs had higher peak loads but lower final

22

displacements. The energy dissipation of the joint with prestressed CPs was

23

lower.

1

12

1

•

Arm2 of the rehabbed joints performed better than the fresh joints. Presumably,

2

the damage during the loading of Arm1 affected the partially anchored joints

3

more than the fully anchored joints. The partially anchored joints had lower initial

4

stiffness than the fully anchored joints.

5

ACKNOWLEDGMENT

6

The present work is financially supported by the Board of Research in Nuclear

7

Sciences. Dr. G. Rami Reddy has helped with the instrumentation for the

8

experiments. The experiments are carried out at the Structural Integrity Testing and

9

Analysis Centre of Indian Institute of Technology Bombay, Mumbai, India. The

10

authors would also like to thank M/s Fyfe India for supplying the composite material

11

system.

12 13 14 15

REFERENCES 1. Alcocer S, Jirsa JO. Strength of reinforced concrete frame connections rehabilitated by jacketing. ACI Structural J 1993;90(3):249–261.

16

2. Ghobarah, A.; Aziz, T. S.; and Biddah, A., ‘‘Rehabilitation of Reinforced

17

Concrete Frame Connections using Corrugated Steel Jacketing. ACI Structural J

18

1997;43:283–294.

19

3. Triantafillou TC, Antonopoulos CP. Design of Concrete Flexural Members

20

Strengthened in Shear with FRP. J Composite for Construction 2000;4(4):198–

21

205.

1

13

1

4. Mukherjee A, Boothby TE, Bakis CE, Joshi MV, Mitra SR. Mechanical Behavior

2

of

Fiber-Reinforced

Polymer-Wrapped

Concrete

3

Effects. J Composite for Construction 2004;8(2):97-103.

Columns—Complicating

4

5. Geng ZJ, Chajes MJ, Chou TW, Pan DYC. The Retrofitting of Reinforced

5

Concrete Column-to-Beam Connections. Composites Science Technology

6

1998;58:1297–1305.

7 8 9 10 11

6. Parvin A, Granata P. Investigation on the Effects of Fiber Composites Concrete Joints. Composites: Part B 2000;31:499-509.

7. Mukherjee A, Joshi M. FRPC Reinforced Concrete Beam-Column Joints under Cyclic Excitation. Composite Structures 2005:70:185-199. 8. Antonopoulos CP, Triantafillou TC. Experimental Investigation of FRP-

12

Strengthened RC Beam-Column Joints. J Composite for

13

2003;7(1):39–49.

14 15 16 17 18 19 20 21 22 23

1

at

Construction

9. Thanasis C, Triantafillou TC. Design of Concrete Flexural :Members Strengthened in Shear with FRP. J Composites for Construction 2000;4:198-205. 10. Antonopoulos CP, Triantafillou TC. Analysis of FRP strengthened RC beamcolumn joints. J Composites Construction 2002;6(1):41–51. 11. Gergely J, Pantelides CP, Reaveley LD. Shear Strengthening of RC T-Joints using CFRP Composites. J Composite for Construction 2000;4(2):56–64. 12. Ghobarah A, El-Attar M, Aly NM. Evaluation of retrofit strategies for reinforced concrete columns. Engineering Structure 2000;22:490-501. 13. Ghobarah A, El-Amoury T. Seismic Rehabilitation of Beam-Column Joints using GFRP Sheets. Engineering Structure 2002;24:1397.

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14. Ghobarah A, El-Amoury T. Seismic Rehabilitation of Deficient Exterior Concrete Frame Joints. J Composites for Construction 2005:9(5):408-416.

3 4 5

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TABLES AND FIGURES

3List of Tables: 4Table 1: Properties of Reinforcing Materials 5Table 2: Test Matrix 6Table 3: Performance of rehabbed specimens 7List of Figures: 8Fig. 1— Stages of rehabilitation 9Fig. 2— Rehabilitation sequence 10Fig. 3— Hysteresis graphs for rehabilitated specimens 11Fig. 4— Envelope Curve for Fresh vs Rehabbed specimens (Arm-1) 12Fig. 5— Energy dissipation curve fresh and rehabbed specimens (Arm-1) 13Fig. 6— Envelope curves for various anchorage lengths (Arm-1) 14Fig. 7— Envelope curve for various levels of prestress (Arm-1) 15Fig. 8— Cumulative energy dissipation (Arm-1) 16Fig. 9— Envelope curves for Arm-2 17Fig. 10— Damage in rehabbed specimens

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1 2

Table 1: Properties of Reinforcing Materials

3 Material

Thickness/ dia (mm)

Tensile Strength

Tensile Modulus

Ultimate Strain

(GPa)

(GPa)

Carbon sheet 644 0.23 gm/m2 (CS)

3.79

230

0.017

Carbon Plate (Composite) (CP)

1.4

2.79

155.1

0.018

Resin

--

0.0214

--

0.05

5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

Table 2: Test Matrix Nomenclature

D-10 D-P-0 1

Anchorage length (Laminate inserted ) Fresh Specimen Partially

Level of prestress (%) of laminate capacity -0 17

D-T-0 B-10 B-P-0 B-T-0 B-P-7 B-T-7 1

Through Fresh Specimen Partially Through Partially Through

0 0 0 7.5 7.5

2 3 4

Table 3: Performance of rehabbed specimens Specimens

Arms

Arm 1 D-10 Arm 2

Arm 1 D-P-0 Arm 2

Arm 1

Yield point Load Deflection (kN) (mm)

Load (kN)

+

32.01

5.339

35.05

17.49

-

-28.68

-5.32

-34.02

-16.74

Direction of motion

+

23.80

9.1

32.74

25

-

-24.32

-9.6

-33

-24

+

45

15.91

47.22

30.15

-

-36.89

-15.59

-49.22

-28.37

+

25.88

44.93

29.15

52.24

-

28.28

39.87

30.16

47.81

+

51.85

15.75

60.58

32.588

-44.5

-17.89

-52.6

-33.08

22.51

31.95

27.90

45.93

-27.87

31.90

-32.57

-42.23

+

27.05

5.97

30.94

10.89

-

-22.97

-6.35

-31.94

-16.02

+

20.71

6.82

25.12

12.61

-

-19.17

-7.05

-24.45

-12.82

+

51.78

14.75

53.45

16.56

-

-37.35

-9.625

-58.01

-34.23

D-T-0 Arm 2

Arm 1 B-10 Arm 2

B-P-0

Arm 1

Arm 2

Arm 1 B-T-0 Arm 2

1

Peak Deflection (mm)

-

+

24.29

34.78

30.42

48.68

-

-26.18

-35.52

-27.84

-49.90

+

43.78

15.33

51.49

26.22

-

-36.34

-14.62

-47

-22.04

+

34.28

14.13

37.89

21.45

-

-37.54

-15.93

-42.82

-22.73

Energy Dissipation (kN-M) 23.89

9.22 33.74 (41.2)* 39.29 (326) 64.69 (171) 33.29 (262) 8.45

6.19 25.41 (201) 24.01 (256) 38.83 (383) 19.78 (220)

18

Arm 1 B-P-7 Arm 2

Arm 1 B-T-7 Arm 2

+

62.34

16.69

65.46

21.93

-

-55.34

-16.34

-59

-19.89

+

24.79

29.73

28.32

40.01

-

-25.63

-25.85

-29.81

-32.27

+

65.46

19.53

71.54

23.59

-

-64.23

-20.13

-68.34

-23.65

+

48.24

14.12

53.37

21.51

-

-38.48

-14.10

-45.53

-20.94

18.21 (115) 11.56 (87) 26.37 (212) 15.06 (143)

1* Figures in parenthesis are % change from control 2 3 4

5 6 7

(a) Making incision

(b) Prestressing unit

8

9 10

(c) CP bonding

(d) CS wrap

11

1

19

1

Fig. 1: Stages of rehabilitation

2 3 4 5 6 7 8

CP partial insertion

CP through insertion

9

Type-T Through inserted CP

10 11

Type-P Partially inserted CP (a) Step-1

Layer 1 column 1500 mm

Layer 2 column Layer 1 beam

Layer 2 beam

1250 mm

12

1

(b) Step-2

(c) Step-3

20

1

CS on front and back faces

2

CS wrap on all the sides

Figure: 2 Rehabilitation sequence

3 4 5 6 Arm-1

Arm-2

60 30

40

20

20

10

Load(KN)

Load(KN)

7 8 9 10 11 12 13 14 15 16 17 18

0 -20

-20

-40

-30

-60 -60

-40

-40

-20

0

20

40

60

-60

-40

-20

0

20

40

60

40

60

Displacement(mm)

Displacement(mm)

(a)

19

D-P-0

80

30

60

20

40

Load(KN)

10

Load(KN)

20 21 22 23 24 25 26 27 28 29 30 31 32

0 -10

20 0

0 -10

-20 -20

-40

-30

-60 -60

-40

-20

0

20

40

60

-40

80

-60

-40

-20

0

20

Displacement(mm)

Displacement(mm)

(b) D-T-0 Arm-1

33

Arm-2

60

40

40

35

20

20

Load(KN)

Load(KN)

34

0 -20

0

-20

-40

36

(c)

-60 -60

-40

-20

0

20

Displacement(mm)

1

40

60

B-P-0

-40

-60

-40

-20

0

20

40

60

Displacement(mm)

21

1 60 40

2

30 20

20 Load(KN)

4

Load(KN)

3

40

0

10 0 -10

-20

-20

5 6

-40

-30 -60

-60 -60

-40

-20

0

20

40

Displacement(mm)

Arm-1

20

40

60

Arm-2

80

30

60

11

14

0

(d) B-T-0

8 9 10

13

-20

Displacement(mm)

7

20 Load (KN)

40 Load (KN)

12

-40

60

20 0

10 0

-20

-10

-40

-20

-60

-30

-80 -30

-20

-10

0

10

20

-40

30

-20

0 20 Displacement (mm)

-10

0

40

Displacement(mm)

15 (a)

16

B-P-7

17 18

80

60

60

20

20

0 Load (KN)

20 21 22 23 24 25 26

40

40 Load(KN)

19

-20 -40

0

-20

-60

-40

-80 -40 -30 -20 -10

0

10

20

30

40

Displacement(mm)

-60

-40

-30

-20

10

20

30

40

Displacement (mm)

27

(c) B-T-7

28

Figure 3: Hysteresis graphs for rehabilitated specimens

29

1

22

1 70 60

D-T-0

50 40

B-T-0

Load KN

30 20

D-10

10

B-10

0 -10 -20 -30 -40 -50 -60 -60

-40

-20

0

20

40

60

Displacement (mm)

2 3

Figure 4: Envelope Curve for Fresh vs Rehabbed specimens (Arm-1) 70

D-T-0

Energy KN-Meter

60

50

40

B-T-0

30

D-10

20

10

B-10

0 0

10

20

30

40

50

60

Displacement (mm)

4 5

Figure 5: Energy dissipation curve fresh and rehabbed specimens (Arm-1)

6 7 8 9

1

23

1 2 3 4

60

60

D-T-0

40

40

6

D-P-0 D-10

20 0

-40

-40

8

-60

-60

-60

-40

9

-20

0

20

40

60

-50

-40

-30

10

-20

-10

0

10

20

30

40

50

Displacement (mm)

Displacement (mm)

(a) D-Type

11

B-P-0

B-10

0

-20

-20

7

B-T-0

20

Load KN

Load KN

5

(b) B-Type

Figure 6: Envelope curves for various anchorage lengths (Arm-1)

12 80

B-T-7

80

60

B-P-7

60

40

B-T-0 B-10

0

40

Load KN

Load KN

20

-20

20

B-P-0

B-10

0 -20

-40 -40

-60 -60

-80 -50

-40

-30

-20

-10

0

10

20

Displacement (mm)

30

40

50

-50

-40

-30

-20

-10

0

10

20

30

40

50

Displacement (mm)

13 14 15

1

(a) Totally inserted Figure 7:

(b) Partially inserted

Envelope curve for various levels of prestress (Arm-1)

24

Energy KN-Meters

40

B-T-0 B-T-7

30

B-P-0 20

B-P-7

10

0

B-10 0

10

1 2

20

30

40

50

Displacement (mm)

Figure 8: Cumulative energy dissipation (Arm-1)

3 4 60

B-T-7

50 40

Load kN

30

B-P-7 B-P-0

20

B-T-0

10

B-10

0 -10 -20 -30 -40 -50 -50

-40

-30

-20

-10

0

10

20

30

40

50

Displacement (mm)

5 6

Figure 9:

Envelope curves for Arm-2

7 8 9 10

1

25

cracks

1 2

Figure 10: Damage in rehabbed specimens

3 4

1

26