Numerical Study on Retrofitting Of Beam Column Joint Strengthened With CFRP

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 03 Issue: 01 | Jan-2016 www.irjet.net p-ISSN: 2395-0072
© 2016, IRJET | Impact Factor value: 4.45 | ISO 9001:2008 Certified Journal | Page 914
NUMERICAL STUDY ON RETROFITTING OF BEAM COLUMN JOINT
STRENGTHENED WITH CFRP
N.NAVEEENA1, M.RANJITHAM2
1PG Student, Civil Engineering, Dr.Mahalingam College Of Engineering & Technology, Pollachi,Tamilnadu,India.
2Assistant professor, Civil Engineering, Dr.Mahalingam College Of Engineering & Technology,
Pollachi,Tamilnadu,India.
Abstarct - In reinforced concrete structures, beam column joint are considered as most damageable structural
element subjected to lateral loads. In the paper a finite element model for exterior beam column joints is presented
to stimulate the seismic behaviour of RC existing structure with design criteria. The Retrofitting of existing structure
is one of the major challenges in the modern civil engineering structures. This paper presents the jacketing method
for strengthening or retrofitting of exterior beam column joint, to enhance their strength and stiffness. An analytical
model is proposed to predict the shear capacity strengthened with carbon fibre reinforced polymer (CFRP).The axial
load were applied at the column top of the surface and held constant during the test. The free end of the beam
subjected to cyclic loading Two specimen one is unstrengthened and another is strengthened specimen with CFRP
were modelled and analysed. An effective re-habitation strategy is in order to increase the ductility of the beam
column joint and transfer the failure mode to beam or delay the shear failure mode. The specimens are then loaded
with step by step load increment procedure to stimulate the cyclic loading in testing. The stress and deformation
results were evaluated and compared their results with strengthened and unstrengthened specimen. The numerical
result shows that the beam column joint strengthened with CFRP can increase their structural stiffness, strength and
energy dissipation capacity.
Keywords:Retroffiting,Exterior beam column joint, Carbon fibre reinforced polymer, Cyclic loading,ANSYS.
1. INTRODUCTION
1.1 GENERAL
In reinforced concrete frames, T connections
(exterior beam column joint) have recognised as a
weaker components when subjected to cyclic lateral
loads. Several damages of connection in general and of a
T connection in a particular section may cause
deterioration of whole performance of frame. Many RC
frames are originally designed to carry only gravity
loads. They lack the ductility and strength to present a
global failure mechanism caused by cyclic loading
conditions. These structures typically have a non-ductile
reinforcement at the beam column joint areas in terms of
inadequate transverse reinforcement and strong column
weak beam design. Strengthening of existing reinforced
concrete structures is now a major part of construction
activity all over the world. The RCC structures
constructed across the world are often found to exhibit
distress and suffer damage, even before service life is
over due to several causes and earthquakes, corrosion,
overloading, change of code provisions, improper design,
faulty construction explosions and fire. For all framed
structures the most important is beam column joint, and
the structural design of joint is neglected during the
design stage, attention is only resisted to provision of
sufficient anchorage for the beam. Unsafe design and
detailing within the joint is dangerous for the entire
structure, even though the structural members
themselves may confirm to the design requirements. It is
well known that joint region in reinforced concrete
framed structures are recognized as very critical as it
transfer the forces and bending moments between the
beams and columns. In most cases during extreme
loading, the beam column joints, if not designed properly
are the most vulnerable component. With the advent of
revised design and detailing codes and detailing codes
and increase in the earthquake vulnerability level of
many regions, the existing structures needs retrofitting
and strengthening.
1.2 TYPES OF BEAM COLUMN JOINTS
Beam column joints are generally classified with
respect to geometrical Configuration and identified as
interior, exterior and corner joints. The fundamental
differences in mechanism the shear requirements, two
types of joints such as interior joint and exterior joint are
considered. With respect to the plane of loading, an

interior beam-column joint consists of two beam on
either side 5 of the column and an exterior beam-column
joint has a beam terminating on one face of the column.
Interior Exterior Corner
Roof interior Roof exterior Roof corner
Figure 1.1 Diferent type of joints
1.3 CARBON FIBRE REINFORCED POLYMER
Carbon fiber-reinforced polymer, carbon fiber-
reinforced plastic or carbon fiber-reinforced
thermoplastic (CFRP, CRP, CFRTP) or often simply
carbon fiber, or even carbon), is an extremely strong and
light fiber reinforced polymer which contain carbon
fiber.
The reinforcement will give the CFRP its
strength and rigidity; measured by stress and elastic
modulus respectively. Unlike isotropic materials like
steel and aluminium, CFRP has directional strength
properties. The properties of CFRP depends on the
layouts of the carbon fiber and the proposition of the
carbon fibers relative to the polymer
Despite its high initial strength to weight ratio,
a degree limitation of CFRP is its lack of a definable
endurance limit. This means theoretically that stress
cycle failure cannot be ruled out. While steel and many
other structural metals and alloys do have estimate
fatigue endurance limits, the complex failure modes of
composites mean that the fatigue failure properties of
CFRP for critical cyclic load applications, engineers may
need to design in considerable strength safety margins to
provide suitable component reliability over its life
service.
ADVANTAGE FOR CFRP
• High tensile strength
• High strength to weight ratio
• Low weight to volume ratio
• Excellent fatigue behavior
• Quick application
CFRP composite was able to strengthen the shear
capacity as well as the ductility of beam column joint.
Table (1) Material properties of CFRP
FRP
composit
e
Elastic
modulu
s
(Mpa)
Major
poison’
s ratio
Tensile
strengt
h
(Mpa)
Shear
modulu
s
(Mpa)
Thic
kne
ss of
lami
nate
mm
CFRP 3.5e3 1
2. EPOXY RESIN
• Epoxy resins are relatively low molecular weight
pre-polymers capable of being processed under
a variety of conditions.
• They exhibit low shrinkage during cure.
• The cured resins have high chemical, corrosion
resistance, good mechanical and thermal
properties, outstanding adhesion to a variety of
substrates, and good electrical properties.
• CFRP improves the compressive strength and
reduces the crack propagation
3. SHEAR FAILURE OF EXTERIOR BEAM-COLUMN
JOINT
A typical detail of exterior beam-column
joint and acting horizontal forces. As acting load
becomes lager, the compressive stress generates at
inside of bent portion of beam bars with the
deterioration of bond performance in straight portion.
Joint shear is considered to be transferred by both of
compressive force in concrete strut formed between
bent portion and beam compressive zone and tensile
force generating in joint transverse reinforcement after
concrete cracking. Joint shear strength is decided by
compressive fracture of concrete strut or yielding of joint
reinforcement. AIJ (Architectural Institute of Japan)
design guideline (AIJ 1999) defines the equation for joint
shear strength as Eqn. 1.1 on the condition of minimum
joint reinforcement volume of 0.3%, where joint
reinforcement is not considered. This design equation
intent to give the shear strength at story displacement of
beam yielding and it tends to show the safety estimation.

Figure 1.2 Force acting at exterior beam-column
joint
Viu Fj bj DJ
Where,
k- Coefficient for joint configuration k= 0.7 for exterior
joint
Ø- Coefficient of existence of transverse
beams,
Ø-1.0(both side0.85 (others)
Fj - fundamental joint shear strength,
Fj-0.8 B
0.7(N/mm2)
bj = joint effective width
Dj = column depth (interior joint) or
development length Ldh of hooked bar
(exterior joint)
4. OBJECTIVE
The main objective of this thesis is to study
about the strength and serviceability of the CFRP
retrofitted beam column joint. Also
• To develop an effective rehabilitation in order
to strengthen the beam column joints to avoid or
delay their shear failure.
• To increase the shear capacity of beam column
joint using carbon fiber reinforced plastic
materials.
• To improve the seismic performance of
damaged building in terms of lateral strength
and serviceability.
• To determine the load deflection behavior of
damaged beam column joint strengthened with
CFRP when it is subjected to cyclic loading
• To compare the behavior of unstrengthened and
strengthened specimen.
5. STRUCTURE DIMENSION
Size of the column 150 x 200 mm
Size of the beam 150 x 200 mm
Height of column 800 mm
Length of the beam 600 mm
6. REINFORCEMENT DETAILS
COLUMN: 4 no’s of 12 mm diameter longitudinal
reinforcement. 8mm diameter bars @ 150mm C/C
distance.
BEAM : 4 no’s of 12 mm diameter bars 8mm diameter
bars @ 100 mm C/C distance
7.1INTRODUCTION
The finite element method is a numerical
analysis technique for obtaining approximate solutions
to a wide variety of engineering problems. ANSYS is a
general purpose finite element (FE) model in ANSYS.
Here a linear analysis is considered throughout is
considered through the study by assuming that there is a
perfect bonding between reinforcement and steel.
7.2 FINITE ELEMENT MODELLING
7.2.1 Concrete modelling
Behaviour of the concrete
Concrete exhibits a large number of micro cracks,
especially, at the interface between closer aggregate and
mortar, even before subjected to any load. The presence
of these micro cracks has a great effect on the
mechanical behaviour of concrete, since their
propagation during loading contributes to non-linear
behaviour at low stress levels and causes volume
expansive near failure. Many of these micro cracks are
caused by segregation, shrinkage or thermal expansive
of the mortar. Some micro cracks may develop during
loading because of the difference in stiffness between
aggregate and mortar. Some micro cracks may develop
during because of the difference in stiffness between
aggregate and mortar. Since the aggregate-mortar
interface has a significantly lower tensile strength than
mortar, it constitutes the weakest in the composite
system. This is the primary reason for the tensile
strength of concrete. The response of a structure under
load depends to a large extent on the stress strain
relation of the constituent materials and the magnitude
of stress. Since concrete is mostly in compression, the
stress-strain relation in compression is of primary
interest.
7.2.2 Element properties
SOLID65 is used for 3-D modelling of solids with
or without reinforcing bars (rebar). The solid is capable
of cracking in tension and crushing in compression. In
concrete applications, for example, the solid capability of
the element may be used to model the concrete while the
rebar capability is available for modelling reinforcing
behaviour. Other cases for which the element is also
applicable would be reinforced composites (such as fibre
glass), and geological material 9such as rock). The

element is defined by eight nodes having three degree of
freedom at each node: translations in the nodal x, y, z
directions.
7.2.3 Steel reinforcement
To model concrete reinforcing, discrete
modelling is used by assuming that bond between steel
and concrete is 100 percent. Beam column has six degree
of freedom at each node. These include translations in
the x, y, z directions and rotations about the x, y, z
directions. This element is well-suited for linear, large
rotation, and large strain nonlinear applications.
7.2.4 Laminates
To model laminated composites SHELL 91 is used.
It may be used for layered applications of a structural
shell model or for modelling thick sandwich structures.
Up to 100 different layers are permitted for applications
with the sandwich option turned off. When building a
model using an element with fewer than three layers
SHELL91 is more efficient than SHELL 99.
7.3 MATERIAL PROPERTIES
Linear analysis considered for modelling RC
beam column, table summarizes the material linear
properties and elements used in the modelling
Table ( 2 ) Different Material Property
Materi
als
Densi
ty
(kg/
m3)
Elasti
c
modu
lus
(Mpa
)
Poiso
n’s
ratio
Fc2
8
(Mp
a)
Fy
(Mp
a)
Elem
ent
used
Concret
e
2200 2236
0
0.15 20 - SOLID
65
Reinfor
cing
steel
7850 2e5 0.3 -
415
Beam
188
8. EXTERIOR BEAM COLUMN JOINT WITHOUT CFRP
WRAPPING
The structural geomentry of exterior beam column
joint has been modelled for the mentioned dimension
and analysed using ANSYS. The exterior beam column
joint has been analysed without CFRP wrapping. The
bottom of the column is constrained in all degree of
freedom. The cyclic load of up to 30KN is applied on the
beam
Figure 8.1 The exterior beam column joint model
Figure 8.2 Mesh model for exterior beam column joint
without wrapping
Figure 8.3 Deflection for concrete exterior beam column
joint without cfrp wrapping

Figure 8.4 Equivalents stresses for concrete the beam
column joint without cfrp wrapping
9. EXTERIOR BEAM COLUMN JOINT WITH CFRP
WRAPPING
The structural geomentry of exterior beam column
joint has been modelled for the mentioned dimension
and analysed using ANSYS. The exterior beam column
joint has been analysed without CFRP wrapping. The
bottom of the column is constrained in all degree of
freedom. The cyclic load of up to 60KN is applied on the
beam. The thickness of wrapping of CFRP is 1.5mm.
Poison ratio is 0.22.young modulus 230000Mpa. And it
is wrapped on300mm length on all sides.
Figure 9.1 The exterior beam column joint model with
cfrp
Figure 9.2 Mesh model for exterior beam column joint
with cfrp wrapping
Figure 9.3 Deflection for exterior beam column joint with
cfrp wrapping
Figure 9.4 Equivalent stress for concrete the beam
column joint with cfrp wrapping

Chart 1 Load vs deflection curve result and discussion
In this chapter the numerical results of both with
CFRP wrapping and without CFRP wrapping are
interpreted. Their behaviour throughout the analysis is
studied from the recorded data obtained from the
deflection behaviour and load carrying capacity using
ANSYS. The strengthened and unstrengthened beam
column joints are tested for their ultimate strength.
1. The load carrying capacity of the retrofitted
specimen is 30% more than the unstrengthened
specimen.
2. The load deformation characteristic also
improves to the large extent in case of
retrofitted specimen over unstrengthened
specimen.
3. The ductility of the retrofitted specimen will be
more when compared with the normal specimen
4. CFRP retrofitting specimen of the beam column
joint shifted the failure of the joint from column
portion to the beam portion of joint which will
prevent progressive collapse.
10.CONCLUSION
The following observations and conclusions can be
drawn based on the analytical results of the study.
1. Comparing the numerical investigation we can
confirm that the deflection in the strengthened
specimen is comparatively lesser than that of
the unstrengthened specimen.
2. It is observed that the stress in the specimen is
better in the retrofitted with CFRP specimen
when compared with the normal specimen
without CFRP wrapping.
3. From the overall study, it can be concluded that
the strengthening with CFRP structure will
increase the serviceability of the structure.
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