IRJET- Experimental Investigation on Seismic Retrofitting of RCC Structures

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 06 Issue: 05 | May 2019 www.irjet.net p-ISSN: 2395-0072
© 2019, IRJET | Impact Factor value: 7.211 | ISO 9001:2008 Certified Journal | Page 2028
EXPERIMENTAL INVESTIGATION ON SEISMIC RETROFITTING OF RCC
STRUCTURES
Jansi Rani K1, Subathra.S2, Sekar. A3
1Post Graduate Student, Structural Engineering, New prince Bhavani College of Engg & Tech, Tamil Nadu, India
2Asst professor, Dept of Civil Engg, New prince Bhavani College of Engg & Tech, Tamil Nadu, India
3Head of Department, Dept of Civil Engg, New prince Bhavani College of Engg & Tech, Tamil Nadu, India
---------------------------------------------------------------------***----------------------------------------------------------------------
Abstract - Beam-column joints are recognized as the critical
and vulnerable zone of a Reinforced Concrete (RC) moment
resisting structure subjected to seismic loads. During an
earthquake, the global response of the structure is mainly
governed by the behavior of the joints. If the joints behave in a
ductile manner, the global behavior generally will be ductile,
whereas if the joints behave in a brittle fashion then the
structure will display a brittle behavior. The joints of old and
non-seismically detailed structures are more vulnerable and
behave poorly under theearthquakescomparedtothejointsof
new and seismically detailed structures. Therefore, the joints
of such old structures require retrofitting in order to deliver
better performance during earthquakes.. This paper reportsa
experimental investigationscarriedoutforseismicretrofitting
of RC beam-column joints using concrete jacketing. The
seismic rehabilitation process aims to improve seismic
performance and correct the deficiencies by increasing
strength, stiffness or deformation capacity and improving
connections. The present study focuses on the behavior of
reinforced concrete beam-columns strengthened using
concrete jacketing subjected to cyclic loading
Key Words: Seismic, Retrofit, Jacketing, strengthening,
ductility.
1. INTRODUCTION
Reinforced concrete (RC) structures designed only
for gravity loads proved their performance under
conventional gravity loads. However, their performance is
questionable under seismic-type loading; the facts are
witnessed by the structural failures observed during
earthquakes worldwide. Observation of the damage caused
by strong earthquakes has highlighted the typical collapse
mechanism of structural elements. Hence, both for existing
structures and newly designed structures, a structural
mechanism has to be evolved in a way so that the seismic
energy introduced into the structure must be dissipated
within the structure. Energy dissipation takes place mainly
through inelastic behavior of the structural system sincethe
structure must be damaged to dissipate energy. If seismic
energy is dissipated at locations that make the structure
unable to satisfy the equilibrium of forces, collapse is
inevitable. Generally for avoiding any collapse in column or
in joint, a commonly termed “strong column–weak beam”
concept is followed over “strong beam–weak column”
concept. Post earthquake examination shows that one ofthe
weakest links in the lateral load resisting system is the
beam–column joints, especially exterior ones because of a
sudden geometric discontinuity and also they are not
confined by beams from all the sides. The beam–column
joints with inadequate or no transverseshearreinforcement
have proved deficient and are likely to experience brittle
shear failure during earthquake motions. Strengthening of
RC beam–column joints has received much attention during
the past two decades. Seismic retrofitting of reinforced
concrete structures is aimed at strengthening structures, in
general, and components, in particular, to achieve more and
consistent strength ductility and energy dissipation.
Numerous researches carried out on different retrofit
techniques including the use of concrete jackets, boltedsteel
plates, and FRP sheets, were considered in the structural
upgrading, especially for columns and beam–column joints
in the moment-resisting frames. The purpose of the
rehabilitation is to prevent columns or joints from a brittle
shear failure, and shift the failure towards a beam flexural
hinging mechanism, which is a more ductile behavior.
2. LITERATURE REVIEW
Giuseppe Oliveto And Massimo Marletta (2005)[1]
considered the retrofitting of buildings vulnerable to
earthquakes and briefly described the main traditional and
innovative methods of seismic retrofitting. Among all the
methods of seismic retrofitting, particular attention was
devoted to the method which was based on stiffness
reduction. This method was carried out in practice by
application of the concept of springs in series, which lead in
fact to base isolation. One of the two springs in series
represented the structure and the other represented the
base isolation system. The enhanced resistance of the
buildings to the design earthquake clearly showed the
effectiveness of the method, while a generally improved
seismic performance also emerged from the application.
Yogendra Singh (2003)[2] large number of existing
buildings in India is severely deficient against earthquake
forces and the number of such buildings is growing very
rapidly. This has been highlighted in the past earthquake.
Retrofitting of any existing building is a complex task and
requires skill, retrofitting of RC buildings is particularly
challenging due to complex behaviour of the RC composite

material. The behaviour of the buildings during earthquake
depends not only on the size of the members and amount of
reinforcement, but to a great extent on the placing and
detailing of the reinforcement. The construction practices in
India result in severe construction defects, which make the
task of retrofitting even more difficult. Step to step
procedure given below-
 Setting of goals and performance level of building and
estimation of seismic hazard.
 Systematic visual inspection and study of available
drawing and documents.
 In situ investigation for strength and degradation of
material and preparation of as built drawing.
 Identify deficiencies and scheme for detailed
investigation.
 Detailed evaluation of strength, ductility, deterioration.
 Design of Retrofitting scheme based on evaluated
deficiencies.
 Evaluation of Retrofitted building.
Pampanin and Chiristopolos [3,4], panel zoneofthejoints
was protected by migrating the plastic hinge some distance
away from the face of the column and by redirecting the
beam shear forces to the column through axial straining of
the haunch. The method causes a decrease of the maximum
drift in the structure.
Shafaei et al. [5,6] suggested a retrofit method for concrete
joint reinforced by deformed bars. In this method, the
connection area was strengthened by steel angles
prestressed by cross ties where stiffeners were welded to
the angles. The proposed method shows significant
enhancement of the seismic capacity of thejoints,interms of
strength, stiffness, energy dissipation and ductility. Also the
technique improved the bond between longitudinal
reinforcement and concrete in the joint.
The behaviour of FRP wrapped concrete cylinders with
different wrapping materials and bonding dimensions has
been studied by Lau and Zhou [7] using the finite element
method (FEM) and other analytical methods. It was found
that the load-carrying capacity of the wrapped concrete
structure is governed by mechanical properties such as
tensile elasticity modulus and Poisson’s ratio of the
wrapping sheet.
Zhao and Feng (2003) [8], investigated experimentallythe
seismic strengthening of RC columns with wrapped CFRP
sheets. The ductility enhancement with the confinement of
CFRP sheets was studied by the strain development and
distribution in the CFRP sheets. Based on the experimental
results, a confinement factor of CFRP and an equivalent
transversal reinforcement index were suggested. In spite of
the extensive work onreinforcedconcretecolumns,very few
researchers have worked on reinforced concrete columns
strengthened using FRP subjected toreversedcyclic loading.
Experimental Program of Beam Column Joint on
Concrete Jacketing
Description of the Specimen
A typical beam–column joint with detailing as per IS
456:2000 (IS 2000) was scaled down to laboratory
conditions. The specimens were subjected to reverse cyclic
loading and their performance wasexaminedforlateral load
capacity. The specimens were classified intotwotypes.Type
1, the Control Specimens (CS), was cast with transverse
reinforcement detailing as per IS 456:2000 and SP 16: 1980
(IS 1980) representing non ductile joint. Type 2,
conventionally Retrofitted Specimen (CR).
Fig-1: Dimension and reinforcement details of control
specimens (CS)
The column was rectangular in shapewithdimensions 100×
140 mm and the beam with dimensions 100 × 140 mm with
an effective cover of 15 mm in all specimens. A 30 mm
concrete jacket over a length of 450 mm on the column and
250 mm on the beam is provided. The concrete jacket was
provided as per the guidelines given in Arya and Agarwal
(2009). Ties with 135° hooks [as per guidelines IS
13920:1993 (IS 1993)] were provided in the concrete
jacketing region as shown in Fig 2.
Preparation of Specimen
The specifications of the materials used to cast the
specimens are as follows: The cement used was Portland
Pozzolona cement (fly ash based) conforming to IS
1489:1991 (Part 1) (IS 1991). Manufactured sand (M-sand)
conforming to zone II as per IS 383:1970 (IS 1970) wasused
as fine aggregate. Crushed granite stone of maximum size
not exceeding 8 mm was used as coarse aggregate. The mix

design was carried out as per IS 10262:2009 (IS 2009). The
mix proportion was 1:1.569:2.769 by weight and the water
cement ratio was kept as 0.40. The 28-day average
compressive strength from 150 mm cube test was 34.15
N/mm2. High yield strength bars were used as longitudinal
reinforcement and ties. The yield stress of reinforcement
was 432 N/mm2. All the specimens were cast in horizontal
position inside a steel mold. For jacketing the retrofitted
specimens, the surface of two control specimens were
cleaned for removal of dirt, had their sharp edges chipped
off, and their surfaces roughened for facilitating bonding
between old and new concrete as shown in Fig. 4. A
reinforcement cage was placed around the joint region. The
entire assembly was positioned inside steel mold for
concreting. Retrofitted (Fig. 4) specimens were cast
simultaneously with the same mix for better comparison of
performance. Specimens were demolded after24handthen
cured in curing tank for 28 days.
Fig-2: Dimension and reinforcement details of
conventionally retrofitted specimens (CR)
Test Setup and Instrumentation
The test setup in the Laboratory is shown in Fig. 5. The
column was mounted vertically with the hinged supports at
both upper and lower ends, which were tightly fastened to
the testing frame by two MS clamps using bolts. Cyclic
loading was applied by two 196.20 kN (20 t) hydraulicjacks,
one kept fixed to top of the loading frame and the other to
the bottom of the loading frame. Reverse cyclic load was
applied at 75 mm from the free end of the beam portion of
the assemblage. A schematic diagram of the test setup is
shown in Fig. 6. The test was load-controlled and the
specimen was subjected to an increasing cyclic load up to
failure. The load increment chosen was 1.962 kN (0.2 t). The
specimen was first loaded up to 1.962 kN and unloaded and
then reloaded on the reverse direction up to 1.962 kN. The
subsequent cycles were also loaded in a similar way. Fig. 7
shows the loading sequence of the test assemblages. To
record loads precisely, load cell with least count 0.981 kN
(0.1 t) was used. The specimens were instrumented with
Linear Variable Differential Transducer (LVDT, SYSCON
Instruments, Bangalore) having least count 0.1 mm to
measure the deflection at the loading point. MS plates were
provided at the point of loading to avoid local crushing of
concrete. A computer-based data acquisition system was
used for capturing data.
Fig- 3: Casting of control specimens (CS)
Fig.-4: Casting of retrofitted specimen
Fig.-5: Test setup in the laboratory

Fig-6: Schematic diagram of test setup
Fig- 7: Sequence of cyclic loading
Results and Discussion
The test results are presented in the form of load-
deformation hysteretic curves, load-deformation envelope
curves, energy dissipation charts, and ductility charts. The
observations during the test are briefly described.
Cracking Patterns and Failure modes
Figs. 8,9 show the crack patterns and failure modes of the
tested specimens. The failure of nonductile control
specimens were characterized by the formation of cracks
near the joint. The first crack occurredatbeam–columnjoint
at third loading cycle when the load reached 5.886 kN in
both positive and negative cycle of loading. The initial
diagonal hairline crack on the joint occurred at the fourth
cycle of loading when the load reached 7.848 kN in both
positive and negative cycles. The specimens failedduetothe
advancement of crack width at the interface between beam
and column and X-shaped cracks in the joint region. The
concrete wedge mechanism was also observed, i.e.,concrete
at the rear side of column became detached in a wedge
shape. The X-shaped cracks are due to the absence of
stirrups in the joint region, and the detachment of concrete
Fig.-8: Failure pattern of control specimen (CR)
Fig.-9: Failure pattern of conventionally retrofitted
specimen
wedge was due to inadequate development length of beam
bars at joint. The retrofitted and monolithically jacketed
specimens performed better in terms of ultimate load
carrying capacity, energy dissipation, and ductility. In
retrofitted specimens, the cracking occurred in the beam at
the interface of jacket, which shows the shifting of plastic
hinge formation beyond the joint region. The cracking
patterns in the strengthened specimens were similar and
also have better performance than that of the control
specimen. The first crack itself occurred in the beam only at
6th cycle, which was at 4th cycle in joint region for the
control specimen. The cracking started at jacket face on the
beam and cracks widened further as the load increased. At
the ultimate load, the failure occurred in the beam and also
minor cracks developed in the jacket. Thus, it is evident that
the concrete jacketing around joint region is capable of
transferring the failure to the beam, thus exhibits an
appreciable seismic behaviour through plastic hinge
formation in the beam.

Ultimate Load Carrying Capacity
Based on the experimental results,theultimateloadcarrying
capacity of retrofitted specimens is found higherthanthatof
control specimens, as shown in Table 1. The control
specimens sustained an ultimate load of about 9.81 kN. The
retrofitted specimens with the conventional ties in the
concrete jacket (CR) was capable of attaining higher values
of ultimate load carrying capacity, i.e., loads 1.40 times of
the control specimens.
Energy Dissipation
As a measure of the dissipated energy of the specimens, the
area under the load displacement curves for all cycles were
computed and called as energy that could be dissipated by
the specimens before the specimen lost its stability. In the
evaluation of earthquake resistance, energy dissipation
capacity of a structure is traditionally associated with the
shape of the load displacement hysteretic loops Figs. 10–11
represent the hysteresis loop for all the specimens. Table 2
shows the average energy dissipation capacity in upward
and downward loading for the testedspecimens.Itisevident
that the energy dissipation of retrofitted specimens
exhibited energy dissipation values of 2.97 times that of the
control specimens
Sp
eci
me
n
Yield Load Ultimate Load
%
incr
ease
Down
ward
direct
ion
Upw
ard
dire
ctio
n
Aver
age
Down
ward
direct
ion
Upw
ard
dire
ctio
n
Av
era
ge
CS 7.85 7.85 7.85 9.81 9.81
9.8
1
-
CR 10.99
10.9
9
10.9
9
13.73
13.7
3
13.
73
40
Table-.1: Ultimate Load Carrying Capacity of Test
Specimens
Fig.-10.:Hysteresis curves for control specimens (CS)
Fig.-11: Hysteresis curves for retrofitted specimen (CR)
specimen
Energy dissipation capacity in
kNmm
Increase in
energy
dissipation
capacity
Downward
direction
Upward
direction
Average
CS 113.60 103.72 108.66 -
CR 222.37 217.13 220.25 2.02
Table -2: Energy Dissipation Capacity for Tested
Specimens
Displacement Ductility
The displacement ductility is the ratio between the
maximum and yield displacement for each specimen,
determined from the load displacement envelope curves.
The displacement ductility values for control specimens are
lower and resulted in poor seismic performance. This is due
to the non optimal reinforcement details and absence of
shear reinforcement in the joint region. The upgraded
specimens show better seismic performance in terms of
displacement ductility, which is due to the increased
concrete section and additional reinforcement around joint
region. Retrofitted specimens CR show a ductile
performance withdisplacementductilityvalues84.32higher
than that of the control specimens.
3. CONCLUSIONS
Based on the experimental results in the present study, the
following conclusions can be drawn:
1. In the non ductile beam–columnjoints,thediagonal cracks
were developed in the joint region leadingtoglobal failureof
the structure.
2. The specimen with conventional retrofitting (CR) shows
40, 103, and 84% increases in ultimate load, energy
dissipation, and displacement ductility, respectively,
compared with the control specimen (CS).

REFERENCES
[1] Giusepe Oliveto, Massimo Marleta, (2005), seismic
retrofitting of reinforced concrete buildings using
traditional and innovative techniques, ISET journal of
earthquake technology, 42(2-3), pp 21-46.
[2] Yogendra Singh, (2003), “ChallengesinretrofittingofRC
buildings”, Workshop on retrofitting of structures IIT
Roorkee, pp 29-44.
[3] Pampanin S, Christopoulos C, Chen TH. Development
and validation of a metallic haunch seismic retrofit
system for existing under-designedRCframebuildings. J
Earthquake Eng & Struct Dyn 2006; 35:1739–66.
[4] Genesio G, Eligehausen R, Pampanin S. Application of
post-installed anchors for seismic retrofit of RC beam-
column joints: design method. In: Proceedings of the
Ninth Pacific conference on earthquake engineering,
building an earthquake-resilient society,Auckland,New
Zealand,2011.
[5] Shafaei J, Hosseini A, Marefat M. Seismic retrofit of
external RC beam–column joints by joint enlargement
using prestressed steel angles. J Eng Struct
2014;81:265–88.
[6] Shafaei J, Zareian M, Hosseini A, Marefat M. Effects of
joint flexibility on lateral response of reinforced
concrete frames. J Eng Struct 2014; 81:412–31.
[7] Lau, K. T.; Zhou, L. M. (2001). The mechanical behaviour
of composite-wrapped concrete cylinders subjectedto
uniaxial compression load, Composite Structures .52:
189–198.
[8] K. Zhang et al. (2003). Experimental study on seismic
strengthening ofRCcolumnswithwrappedCFRPsheets.
Construction and Building Materials,499-506.

IRJET- Experimental Investigation on Seismic Retrofitting of RCC Structures

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