This document summarizes an experimental study on the behavior of interior beam-column joints in reinforced concrete frames wrapped with fiber-reinforced polymer (FRP). Sixteen beam-column joint specimens were tested under cyclic loading, with variations in reinforcement detailing per Indian codes IS 456-2000 and IS 13920-1993, and use of FRP wrapping and fiber-reinforced concrete. The results showed that joints designed according to IS 13920-1993 had smaller cracks and higher load capacity than those per IS 456-2000. FRP wrapping and fiber-reinforced concrete improved joint ductility, increasing maximum deflection by up to 25% compared to unwrapped specimens. Specimens with two layers of FRP wrapping and 0.

1. ASIAN JOURNAL OF CIVIL ENGINEERING (BHRC) VOL. 17, NO. 8(2016)
PAGES 1151-1166
BEHAVIOUR OF INTERIOR BEAM-COLUMN JOINT WITH FRP
WRAPPING
P. Gajalakshmi
, K. Sriram and U. Elakeya
Department of Civil Engineering, B.S. Abdur Rahman University, Chennai, India
Received: 20 February 2016; Accepted: 22 May 2016
ABSTRACT
Beam column joint is an important component of a reinforced concrete moment resisting
frame and it should be designed and detailed properly, especially when the frame is
subjected to earthquake loading. Failure of beam - column joints during earthquake is
governed by bond and shear failure mechanism, which are brittle in nature. Therefore, it is
necessary to study the behavior of reinforced concrete joints under earthquake loading. Here
an attempt is made to observe the difference in the behavior of beam – column joint
designed using IS 13920 – 1993 and IS 456 – 2000 which is studied under simulated seismic
loading and also the behavior of the joint is studied when it is wrapped with FRP. Fiber
reinforced concrete is used to improve the ductility of the member.
Keywords: Beam-column joint; ductility; fibre reinforced polymer; fibre reinforced
concrete; FRP wrapping
1. INTRODUCTION
Beam-column joints are one of the most critical elements of reinforced concrete moment
resisting frames subjected to lateral seismic loading. Lateral loads may result in significant
shear forces in beam-column joints which may lead to extensive joint deterioration if the
structure is not proportioned well to resist the lateral loads. The most crucial part of the
design of reinforced concrete frames is to be able to use the maximum capacity of their
structural members. To provide that, each beam column joint must maintain its integrity
during a severe earthquake and allow its connecting beam members to reach their ultimate
capacities. To maintain the integrity of the beam-column joints - The axial load carrying
capacity must be sustained by limiting the joint rotations, transverse reinforcement must be
provided in the joint region and longitudinal steel in beam should be minimized in order to
prevent joint stiffness degradation due to the cracks developing in the joint core and due to
the loss of bond between the concrete and reinforcement.

E-mail address of the corresponding author: gajalakshmi@bsauniv.ac.in (P. Gajalakshmi)

2. P. Gajalakshmi, K. Sriram and U. Elakeya1152
There are several aspects that should be considered during the design of a structure,
including the economical aspect. To make the structure economically feasible, inelastic
deformations should be allowed during a severe earthquake as required by the current
building codes. At the same time, it is important to ensure that the plastic hinges or
significant plastic deformations occur in less critical regions of the building frame.
Formation of plastic hinges inside the beam-column joint regions or in columns may result
in partial or complete collapse of the building. The preferable regions for the plastic hinges
are the column faces where the beams frame into the columns. Therefore, the damage to the
reinforced concrete beam-column joints should be limited and the beams should be able to
develop plastic hinges at their ends during a severe earthquake.
Several works has been carried out in the past to observe the behavior of beam column
joint under seismic loading. Mukherjee and Joshi [1] investigated on the behavior of fiber
reinforced polymer composites reinforced concrete beam-column joints under cyclic
excitation. Pampanin et al. [2] suggested possible modifications for the inaccuracy of
traditional shear degradation models for exterior joints in predicting concrete wedge brittle
failure mechanisms. Pantelides and Reaveley [3] described regarding the use of externally
applied carbon fiber-reinforced plastic (CFRP) jackets for seismic rehabilitation of
reinforced concrete interior beam-column joints, which were designed for gravity loads.
Concrete crack widths for the as-built specimens and the extent of CFRP de-lamination for
the rehabilitated specimens at various drift ratios are reported in their study. Pimanmas and
Supaviriyakit [4] made a detailed study on cyclic behaviour of non-seismically designed
interior reinforced concrete beam-column connections. Kusuhara et al. [5], conducted
experiment on reinforced concrete interior beam-column joint subassemblage with
eccentric beams. Eccentric beam-column joints was used in three specimens of one third
scale reinforced concrete interior beam-column subassemblages were constructed and
loaded to failure by statically cyclic load simulating earthquake, to obtain fundamental
data including three dimensional deformation of beam-column joint.
Leong and Li [6] conducted an experimental study on the behaviour of High strength
concrete (HSC) reinforced beam-column joints with column axial compressive load. The
confinement as a result of column axial compressive load was found to improve the
bond performance of beam-column joint where the confinement was obtained with axial
compressive load that acted to exert clamping action across splitting cracks.
Confinement that was transverse to the direction of the embedded bar significantly
improved the bond performance of joint. Seismic Behaviour of Reinforced Concrete
Interior Beam-Wide Column Joints Repaired using fibre reinforced polymer has been
studied by Li and Kai [7]. It was demonstrated that the repair of damaged RC beam-wide
column joints by using FRP can restore the performance of damaged RC joints with
relative ease, suggesting that the repair of beam-column joints is a cost-effective
alternative to complete demolition and replacement. The experimental results showed that
specimens with small to medium column tributary area were vulnerable to brittle joint shear
failure, while specimen with large column tributary area could achieve moderately ductile
yielding, even though the ductile reinforcement detailing was not provided.

3. BEHAVIOUR OF INTERIOR BEAM-COLUMN JOINT WITH FRP WRAPPING 1153
Li and Kai [7] conducted study on the seismic behavior of reinforced concrete interior beam-
wide column joints repaired using FRP laminates and concluded that FPR laminated repaired
beam column joints behave well under seismic conditions. Francesca et al. [8] conducted study
on the use of FRP fabric for strengthening of reinforced concrete beam-column joints. Ganesan
et al. [9] conducted study on the steel fibre reinforced high performance concrete beam-column
joints subjected to cyclic loading.
2. EXPERIMENTAL INVESTIGATION
2.1 Details of experimental program
STAAD PRO model of multistoried building located in Chennai has been developed and
analyzed, which is falling under the seismic zone II. The structure is five storey two bay
frames including 1.5 m foundation depth. The maximum moment occurred at the ground
floor roof level, and that particular interior beam- column joint is taken for the experimental
study. The specimens were designed for seismic load according to code IS 1893(Part-I):
2002 [10]. The details of the specimens taken for experimental study given in Table 1.
2.2 Details of specimen
The test specimen was reduced to 1/5th
scale to suit the loading arrangement and test
facilities. The prototype model size has been reduced to 150 x 200 mm for both beam and
column specimens. The length of the beam is taken as 600 mm and height of the column is
taken as 800 mm.
Table 1: Design data
Proto type
(STAAD)
Beam size 750 x 1000 mm
Column size 750 x 1000 mm
Tension reinforcement in beam 1100 mm2
Compression reinforcement in beam 780 mm2
Column main reinforcement 2200 mm2
Model
Beam size 150 x 200 mm
Column size 150 x 200 mm
Tension reinforcement in beam 220 mm2
Compression reinforcement in beam 150 mm2
Column main reinforcement 440 mm2
Table 2: Nomenclature of the speciemen
S.NO DETAILING TYPE LEGEND
1 IS 456-2000
Control specimen S1Control specimen + FRP 1 layer S2
Control specimen + FRP 2 layer S3
Fiber reinforced concrete 0.5% volume fraction S4Fiber reinforced concrete 0.5% volume fraction +1
layer
S5
Fiber reinforced concrete 0.5% volume fraction +2
layer
S6

4. P. Gajalakshmi, K. Sriram and U. Elakeya1154
2 IS 13920-1993
Control specimen S7
Control specimen + FRP 1 layer S8
Control specimen +FRP 2 layer S9
Fiber reinforced concrete 0.5% volume fraction S10
Fiber reinforced concrete 0.5% volume fraction +1
layer
S11
Fiber reinforced concrete 0.5% volume fraction +2
layer
S12
2.3 Material properties
The concrete mix was designed for a cube compressive strength of 60 Mpa at 28 days. The
design mix of 1:1.58:2.26 with water cement ratio of 0.41, using 20 mm size (max) coarse
aggregate along with this super plasticizer conplast SP 430 and silica fume is added in the
ratios 0.008 and 0.11 respectively, the mix design was based on ACI committee 211.1.1991
recommendations. From the concrete mix, concrete cubes and cylinders were prepared and
tested to obtain the actual material properties.
Fe 415 steel bars of diameters 12mm and 8 mm were used as reinforcement for beam –
column joints. The yield strength of 12mmφ and 8mmφ steel is 436N/mm2
and 287N/mm2
respectively.
For the fiber reinforced concrete, hooked end steel fibers of length and diameter 60 and
0.75 mm respectively with aspect ratio 80, tensile strength – 1225 Mpa and elastic modulus -
210000 Mpa were used. GFRP unidirectional cloth (ASTM D 638) of thickness 3mm and
5mm is used as wrapping material in beam – column joint, whose properties are given in the
Table 3.
Table 3 : Properties of GFRP
Property
Uni -Directional Cloth (ASTM D 638)
3mm Thickness 5mmThickness
Elasticity Modulus (MPa) 13965.63 17365.38
Ultimate Elongation (%) 3.02 2.60
Tensile Strength (MPa) 446.90 451.50
2.4 Reinforcement detailing
The reinforcement details for IS 456-2000 [11] detailing of beam column joint are shown in
Fig. 1 and Fig. 2 Main reinforcement provided in the beam was 8 mm diameter bars, 3 No’s
at top and 12 mm diameter 3 No’s at bottom. The stirrups are 8 mm diameter bars at 100
mm c/c. The longitudinal reinforcement provided in the column was 4 No’s of 12 mm
diameter bars equally distributed along four sides of column. The column confinements are
8 mm diameter bars at 100 mm c/c.
The reinforcement details for IS 13920 – 1993 [12] of beam column joint are shown in
Figs. 3 and 4. Main reinforcement provided in the beam was 8 mm diameter bars, 3 No’s at
top and 12mm diameter 3 No’s at bottom. The stirrups are 8 mm diameter bars at 40 mm c/c
for a distance of 2d, i.e. 340 mm from the face of the column and at 85 mm c/c for

5. BEHAVIOUR OF INTERIOR BEAM-COLUMN JOINT WITH FRP WRAPPING 1155
remaining length of the beam. The longitudinal reinforcement provided in the column was 4
No’s of 12 mm diameter bars equally distributed along four sides of column. The column
confinements are 8 mm diameter bars at 35 mm c/c for a distance of 200 mm from the face
of the column and at 75 mm c/c for remaining length of the column. The wrapping of first
and second layer of FRP is shown in the Fig. 5 to Fig. 7, respectively.
Figure 1. Detailing of beam-column joint as Per
IS 456 - 2000
Figure 2. Form work of beam-column joint
as per IS 456-2000
Figure 3. Detailing of beam-column joint as
Per IS 13920 - 1993
Figure 4. Form work of beam-column joint
as per IS 13920 - 1993
2.5 Test setup and instrumentation
The specimens were tested with the column portion vertical in a 100 ton reinforced
concrete reaction frame as shown in Fig. 8. No axial compression was applied to the
column in order to evaluate a worst-case scenario for the joint core. A hydraulic jack
was used to apply the axial load for both the beam at 5 cm from end. A dial gauge was
provided at the free end of the beam to measure deflection. Hydraulic jack has the
capacity of 50 t and 4 t on both the end of beams respectively. To record the load
precisely a proving ring was used. Loading is applied gradually from 4 kN to 15 kN
respectively on both sides of the beam in forward direction only.

6. P. Gajalakshmi, K. Sriram and U. Elakeya1156
Figure 5. FRP & FRC portion in beam –column joint
Figure 6. First layer wrapping of FRP Figure 7. Second layer wrapping of FRP
Figure 8. Loading setup of beam - column joint

7. BEHAVIOUR OF INTERIOR BEAM-COLUMN JOINT WITH FRP WRAPPING 1157
2.6 Behavior of beam – column joint
In all the specimens, cracks/debonding appeared near the joint after the first crack /
debonded load. The crack pattern showed in Fig. 9 and 10 exhibits the failure process of the
specimen and cracks are appeared near the joint, with the increase in applied load, the cracks
propagated on the upper surface of the beam and the cracks are increased until the peak load
is reached. There is a minimum crack width in IS 13920 control specimen when compared to
IS 456 control specimen. Figs. 11 and 12 show the well failure process of FRP debonded
specimen. Initial crack appeared at the ultimate strength of 16 kN & 20 kN respectively. Fig.
13 and 14 shows, the FRP debonded specimen and the ultimate strength is obtained at the
load of 26 kN & 32 kN, respectively. Fig. 15 and 16 shows, the cracks in the specimens are
appeared after applying the load of 13 kN & 18 kN, respectively. Fig.17 and Fig. 18 show,
FRP specimen debonded after applying the load of 20 kN & 26 kN, respectively. Fig.19 and
Fig. 20 show, FRP specimen debonded after applied the load of 30 kN and 36 kN,
respectively. IS 456 control specimen gives the major cracks near the joints.
Figure 9. Crack pattern in IS S1 specimen Figure 10. Crack pattern in S7 specimen
Figure 11. Debonding of S2 specimen Figure 12. Debonding of S8 specimen

8. P. Gajalakshmi, K. Sriram and U. Elakeya1158
Figure 13. Debonding of S3 specimen Figure 14. Debonding of S9 specimen
Figure 15. Crack pattern in S4 specimen Figure 16. Crack pattern in S10 specimen
Figure 17. Debonding of S5 specimen Figure 18. Debonding of S11 specimen

9. BEHAVIOUR OF INTERIOR BEAM-COLUMN JOINT WITH FRP WRAPPING 1159
Figure 19. Debonding of S6 specimen Figure 20. Debonding of S12 specimen
3. RESULTS AND DISCUSSION
3.1 Load – deflection behavior
A load-deflection plot is shown in Figs. 21 to 26. The envelope curve is obtained by joining
the deflection on each load. A comparison of envelope plots for different specimens was
shown in graphs. Fig. 21 shows the load – deflection behavior of S1 and S7 control
specimen, where (a) and (b) represents interior and exterior beams respectively. From the
Fig. 21, it is inferred that S7 specimen gives the improved percentage of ultimate deflection
7% when compared to the S1 specimen. Fig. 22 shows the result of specimen S2 and S8.
The percentage of ultimate deflection was found to be improved in 14.65% compared to the
S2 specimen. Fig. 23 shows the result between specimen S3 and S9. S9 specimen gives the
improved percentage deflection of 6.2 % compared to the S3 specimen. Fig. 24 shows the
result between specimen S4 and S10. S10 specimen gives the improved percentage
deflection of 25 % compared to the S4 specimen. Fig. 25 gives the results of specimen S5
and S11. The percentage of ultimate deflection was found to be improved in 8.5% compared
to the S5 specimen. Fig. 26 gives the results of specimen S6 and S12. The percentage of
ultimate deflection was found to be improved in 16.6% compared to the S6 specimen.
Figure 21. Load Vs displacement response in S1 & S7 specimen

10. P. Gajalakshmi, K. Sriram and U. Elakeya1160
Figure 22. Load Vs displacement response in S2 & S8 specimen
Figure 23. Load Vs displacement response in S3 & S9 specimen
Figure 24. Load Vs displacement response in S4 & S10 specimen

11. BEHAVIOUR OF INTERIOR BEAM-COLUMN JOINT WITH FRP WRAPPING 1161
Figure 25. Load Vs displacement response in S5 & S11 specimen
Figure 26. Load Vs displacement response in S6 & S12 specimen
3.2 Load carrying capacity
The following graph shows the comparison of initial crack/ debonded load to the ultimate
load of the specimen. Fig. 27 compares the control specimen of S1, S7, S4 and S10
specimen. By comparing both control specimens, ultimate load of S7 was increased about
30% when compared to the S1 control specimen. While comparing FRC specimens, the
ultimate load of S10 was increased about 30% to the specimen S4.
Fig. 28 shows the comparison with the specimen of S1, S8 and S3, S9. In S8 and S9
specimen, the ultimate load was increased about 40% and 25% respectively, when compared
to the specimen S2 and S3.
Fig. 29 illustartes the specimen of S11 and S12 gives an improved ultimate load of about
8.57% and 10% respectively, when compared with the specimen S5 and S11.

12. P. Gajalakshmi, K. Sriram and U. Elakeya1162
Figure 27. Comparison of first and ultimate load
Figure 28. Comparison of FRP debonded and ultimate load
Figure 29. Comparison of FRC, FRP debonded and ultimate load

13. BEHAVIOUR OF INTERIOR BEAM-COLUMN JOINT WITH FRP WRAPPING 1163
3.3 Load – strain behavior
To gain an insight into the behavior of each specimen, local deformations and strains were
measured at critical regions of the specimens. The strain is directly obtained from the
readings measured by electrical strain gauge. The following graph shows the load- strain
behavior of each specimen.
Fig. 31 shows the load-strain behavior of S1 and S7 control specimen. The first yielding
point occurred at 20 kN in S1 control specimen, whereas in S7 control specimen yielding
occurred at 24 kN. The strain in column is minimal in both the specimens.
Fig. 32 shows the load-strain behavior of S2 and S8 specimen. The yielding point is
occurred at a load of 30kN in the specimen of S8. In the S8 column, strain is slightly higher
when compared to the strain measured in S2 column specimen.
Fig. 33 shows the load-strain behaviour of S3 and S9 specimen. The yielding point
occurred at the load of 26 kN in the specimen of S3. The behaviour of strain in column
reinforcement in both the specimen gives the minimum strain value.
Fig. 34 shows the load-strain behaviour of S4 and S10 specimen. The yielding point
occurred at a load of 24 kN in S4 specimen. The difference in yielding load of S4 and S10 is
4kN.
Fig. 35 shows the specimen S5 and S11. The yielding point is occurred at a load of 28kN
in S5 specimen. The strain in column is slightly higher when compared to the S11 specimen.
Fig. 36 gives the load- strain behavior of S6 and S12 specimens. The maximum strain
occurred at load of 24 kN in the S6 specimen. The difference in yielding load of the
specimen was 6kN.
Figure 31. Load Vs strain behavior in S1 & S7 specimen

14. P. Gajalakshmi, K. Sriram and U. Elakeya1164
Figure 32. Load Vs strain behavior in S2 & S8 specimen
Figure 33. Load Vs strain behavior in S3 & S9 specimen
Figure 34. Load Vs strain behavior in S4 & S10 specimen

15. BEHAVIOUR OF INTERIOR BEAM-COLUMN JOINT WITH FRP WRAPPING 1165
Figure 35. Load Vs strain behavior in S5 & S11 specimen
Figure 36. Load Vs strain behavior in S6 & S12 specimen
4. CONCLUSIONS
Based on the experimental investigations carried out on the various specimens, the following
conclusions were drawn,
1. The load carrying capacity, load- deflection and load-strain behavior of the S12 specimen
gives the better results compared to the control specimen S7.
2. The load carrying capacity of the S12 specimen gives an improved ultimate load of
69.23% &120% when compared to the control specimen of S7 and S1 respectively.
3. The load-deflection behavior of the S12 specimen gives an improved deflection of 271%
&300% when compared to control specimen of S7 & S1 respectively.
4. The load-strain behavior of the S12 specimen gives an improved yielding load of 25% &
16.6% when compared to the control specimen of S7 & S1.
5. Load carrying capacity is also increased while using FRP wrapping.
6. The S12 specimen underwent large displacements without developing wider cracks when
compared to the control specimen.
7. To increase the ductility, FRC can be added to the beam-column joints in the earthquake
prone regions.

16. P. Gajalakshmi, K. Sriram and U. Elakeya1166
Beam-column joints can be rehabilitated by using FRP layers.
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