International Journal of Civil Engineering and Technology (IJCIET)
Volume 8, Issue 1, January 2017, pp. 170–188, Article ID: IJCIET_08_01_018
Available online at http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=8&IType=1
ISSN Print: 0976-6308 and ISSN Online: 0976-6316
© IAEME Publication
ANALYSIS AND EXPERIMENTAL STUDY ON
STRENGTH AND BEHAVIOUR OF EXTERIOR
BEAM-COLUMN JOINTS WITH DIAGONAL CROSS
BRACING BARS AND STEEL FIBRES FOR
IMPROVING THE JOINT DUCTILITY
K. Johnson
Research Student, Department of Civil Engineering,
Karunya University, Coimbatore, India
Dr. G. Hemalatha
Professor & Head of Civil Engineering Department,
Karunya University, Coimbatore, India
ABSTRACT
The present work aims to study analytically and experimentally on the seismic performance of
exterior beam column joint to improve the joint ductility with non-conventional reinforcement and
by using steel fibres. Five joint sub assemblages were tested under reverse cyclic loading applied at
the beam end. Beam column joints are critical regions for frames designed for inelastic response to
severe seismic attack. The overall structural safety, especially for joints is due to lack of ductility.
Different parameter of joint using ANSYS modelling was studied and experimentally verified the
results. All these details are presented.
Key words: ANSYS modelling and analysis, beam-column joints, cyclic loading, displacement
ductility, hysteretic loops.
Cite this Article: K. Johnson and Dr. G. Hemalatha. Analysis and Experimental Study on Strength
and Behaviour of Exterior Beam-Column Joints with Diagonal Cross Bracing Bars and Steel Fibres
for Improving the Joint Ductility. International Journal of Civil Engineering and Technology, 8(1),
2017, pp. 170–188.
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1. INTRODUTCION
Seismic zones of low to medium seismicity do not take into consideration for design of reinforced concrete
structures. The reinforcement details of such structures conform to the general construction code of
practice may not adhere to the modern seismic provisions. The reinforced concrete joints are treated as
rigid in the analysis of moment resisting frames. The joint is usually neglected in Indian practice for
specific design and attention being restricted to provision of sufficient anchorage for beam longitudinal
reinforcement and can be acceptable when the frame is not subjected to earthquake loads. A beam column
joint becomes structurally less efficient when subjected to large lateral loads. By increasing the number of
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Analysis and Experimental Study on Strength and Behaviour of Exterior Beam-Column Joints with Diagonal
Cross Bracing Bars and Steel Fibres for Improving the Joint Ductility
stirrups at the joint the joint shear capacity can be increased. When the spacing of stirrups at the joint
becomes closer, the joint will become congested and concrete will not enter into the joint due to
insufficient spacing and this is the practical difficulty facing at site while concreting the beam column
joints. Hence required compaction at the joint will not be attained. By providing non conventional cross
diagonal bars at the joint or by providing steel fibres at the joint, shear capacity of the joint and ductility
can be increased to a great extent. Analysis and experimental results shows increase in load carrying
capacity and shear capacity of the joint with non conventional bars and fibres at the joint. The earthquake
in Turkey and Taiwan occurred in 1999 reported catastrophic failures due to failure of beam-column joints.
Akashu Sharma, R. Eligehausen and G.R.Reddy [1] study on joint shear behavior of poorly detailed beamcolumn connections in RC structures under seismic loads, Part I: Exterior joints. Due to inelastic capacities
of adjoining flexural members, beams and columns, to dissipate seismic energy, the poor design of beam
column joint will lead to failure. Even though other structural members conform to the design
requirements, the beam column joint design failure leads to failure of the entire structure,. S. S. Patil, S. S.
Manekari [2] study on analysis of Reinforced Beam-Column Joint Subjected to Monotonic Loading. The
joints are to be designed and detailed properly. Joints are the weakest point and will develop cracks and
fail first in earthquakes. To Preserve the integrity of the joint sufficiently high by designing and detailing
the joint properly. The ultimate strength should be sufficient to prevent excessive degradation of joint.
Preventing the loss of bond between the concrete and longitudinal beam and column reinforcement, the
crack in the joint can be minimized. The brittle shear failure of the joint can be prevented. Choudhury, A.
M., A. Dutta, and S. K. Deb. (2011) [5]. Moments of opposite signs are developed in columns above and
below the joints during earthquake. During earthquake, at the joint region, shear force of magnitude many
times higher than in the adjacent beams and columns will be developed. Joint failure can result, if not
designed and detailed. Lu, Xilin, Tonny H. Urukap, Sen Li, and Fangshu Lin. [10] Study on Seismic
behaviour of interior RC beam-column joints with additional bars under cyclic loading.
2. ANSYS 16 WORKBENCH (WB)
2.1. Modeling Geometry and Analysis
ANSYS WB 16 is used for the finite element modeling and analysis. The design of Beam Column Joint is
done using ANSYS WB Design Modeler. The ANSYS Design Modeler application is designed to be used
as a geometry editor of existing CAD models. Designers can design models with Design Modeler alone. Its
application is a parametric feature-based solid modeller. and is designed so that designers can intuitively
and quickly begin CAD drawing for engineering analysis pre-processing. In the designing of Beam
Column Joint it is used line body method to design reinforcement bar and fibre. This method gives
advantages of less system resource and analysis time and better result accuracy.2.2Modeling Finite
Element Model:
Modeling the Finite Element model is nothing but the descretization of model into elements. The goal
of meshing in ANSYS Workbench is to provide robust, easy to use meshing tools that will simplify the
mesh generation process. These tools have the benefit of being highly automated along with having a
moderate to high degree of user control. The finite element modeling is done using Elements SOLID185,
and BEAM188.SOILD 185 is used for 3-D modeling of solid structures. It is defined by eight nodes
having three degrees of freedom at each node: translations in the nodal x, y, and z directions. The element
has plasticity, hyper elasticity, stress stiffening, creep, large deflection, and large strain capabilities. It also
has mixed formulation capability for simulating deformations of nearly incompressible elasto plastic
materials. And it is fully incompressible hyper elastic materials. BEAM 188 is suitable for analyzing
slender to moderately stubby/thick beam structures. The element is based on Timoshenko beam theory
which includes shear-deformation effects. The element provides options for unrestrained warping and
restrained warping of cross-sections. The element is a linear, quadratic, or cubic two-node beam element in
3-D. BEAM 188 has six or seven degrees of freedom at each node. A seventh degree of freedom (warping
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magnitude) is optional. This element is well-suited for linear, large rotation, and/or large strain nonlinear
applications.
2.2. Material Properties in ANSYS WORKBENCH and ANSYS Analysis
2.2.1. Loading Systems
The major loads are dead load, live load, imposed (wind) load, snow load, earthquake load imposed in the
structures. The analysis of joints is done with static and dynamic loads. Beams (bending), column (axial),
are static loading nature. Shake similar to that during earthquakes is called dynamic (random) loading.
2.2.2. Engineering Data
Use the Engineering Data cell with the Mechanical application systems or the Engineering Data
component system to define or access material models for use in an analysis. To add an Engineering Data
component system to the Project Schematic, drag the Engineering Data component system from the
Toolbox to the Project Schematic or double-click the system in the Toolbox. Study on Steel fibre
reinforced high performance concrete beam-column joints subjected to cyclic loading [7,8,9,10].
The non linear analysis of Beam Column Joint is done in Static and Transient (dynamic) analysis
system. The acceleration data given for analysis is taken from earthquake data of zone -III. A static load of
17 kN is applied at the tip of the beam and load increased gradually with 6 load steps. Static and dynamic
loading is applied at the joint and studied the behavior. Results taken from zone-III are used for preparation
of FE model.
3. PROPOSED WORK
3.1. ANSYS Modeling of Exterior Beam Column Joints under Static Loading
ANSYS modeling and analysis under static and dynamic loading with different loading conditions using
steel fibers, diagonal steel bars in the joint and at extended in column and beam directions to study the
resistant of shear or bond failure.
Steel fiber = 1% by volume and extending in column and beam directions. Study on Use of fibre
cocktails to increase the seismic performance of beam-column Joints [14,16,17,18].
3.2. Beam Column Joint Design details for ANSYS Modeling
Column size- 175 mm x 150 mm, Beam size- 175 mm (D) x 150 mm(B), Strength of concrete fck- 20
N/mm2., Yield strength of steel fy- 415 N/mm2.Column longitudinal steel- 16 mm diameter- 4 nos.
Column lateral tie- 8 mm diameter @ 150 mm c/c.. Beam main reinforcement steel- 12 mm diameter- 4
nos. Beam stirrups- 8 mm @ 100 mm c/c. Maximum load on column – Pmax. - 336 kN. Beam point loadW max- 17 kN. Column height- 1500 mm, Beam length- 600 mm. RCC beam column joints were designed
for analysis based on IS 1893-2002 Criteria for Earthquake Resistant design of structures and detailing
based on IS 13920-1993 Edition 1.2 (2002-03) on Indian Standard Code of Practice Ductile Detailing of
Reinforced and referring to relevant books[24,25,26,27].
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Analysis and Experimental Study on Strength and Behaviour
Behaviou of Exterior Beam-Column
Column Joints with Diagonal
Cross Bracing Bars and Steel Fibres for Improving the Joint Ductility
3.3. External Beam-Column
Column Joint
J
- Analysis Setup
Figure 1 External joint under static loading
Figure 2 ANSYS 16 modeling static
stat loading.-Deflection
Figure 3 Pu&Wmax- bending stress
Figure 4 Pu&WmaxPu&Wmax shear stress
Figure 5 ANSYS 16 modeling under dynamic loading.-Deflection
loading.
Figure 6 Pu & Wmax- shear stress
Figure 7 External joint static analysis using diagonal bars at the
t joint. Figure 8 Pu & Wmax- deflection
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Figure 9 Pu & WmaxWmax bending
Figure 10 Pu & Wmax - shear
Figure 11 External joint using steel fibers
Figure 12 Pu & Wmax- deflection
Figure 13 Steel fibers extending in beam
Figure 14 Pu & Wmax- deflection
Figure 15 Pu & Wmax- bending
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4. DUCTILITY
Ductility is generally measured in terms of displacement ductility. This is the ratio of the maximum
deformation that a structure or an element can undergo without significant loss of initial yielding resistance
to the initial yield deformation. The displacement ductility of all the models is presented in table 1. It can
be seen that the displacement ductility is more for the beam column joint with additional cross diagonal
bars and additional steel fibres. The percentage increase is 76.03% and 63.01%.The ductility increment is
more for the beam column joint with additional diagonal cross bars than with additional fibres by 13.02%.
It can be seen that the displacement ductility factor for beam column joint with additional cross bracing
bars is 55.32% more than that of normal beam column joints. It can be seen in ANSYS 16 analysis that the
deflection at yield point load and at ultimate load are increasing by using the non-conventional diagonal
bars and steel fibre at the beam column joint. The displacement at ultimate load increases when the
additional cross diagonal bars and additional steel fibres are added at the beam column joint. Also it can be
seen that the results are better for the beam column joints with non-conventional diagonal bars extending
on beam and column directions by .3H and .3B. The ultimate upward displacement is greater than the
downward displacement for all the specimens.
Table 1 Displacement ductility of specimen from ANSYS model.
Displacement (mm)
specimen
yield
ultimate
Displacement ductility
Average
displacement
ductility
Downward
direction
Upward
direction
Downward
direction
Upward
direction
Downward
direction
Upward
direction
A1
3.45
-
12.45
-
3.61
-
3.61
A
4.21
4.85
14.28
16.28
3.39
3.36
3.38
B
3.32
3.63
17.28
19.27
5.20
5.30
5.25
C
4.53
4.35
19.38
33.25
5.27
6.64
5.95
D
3.98
3.78
17.29
22.45
4.34
5.94
5.14
E
3.95
3.93
18.67
24.78
4.72
6.31
5.51
A1- Normal (IS 456) Static loading, A-Normal (IS 456) transient loading, B-With additional diagonal
bars at the joint - transient loading, C-With additional diagonal bars at the joint and extending in beam
(.3B) & column(.3H)- transient loading. D-With additional fibre at the joint- transient loading, E-With
additional fibre at the joint and extending in beam (.3B) & column (.3H) - transient loading.
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Table 2 Yield load and ultimate load of specimen from ANSYS 16 model
Yield load (kN)
Ultimate load (kN)
Specimen
Downward
direction
Upward
direction
Average(P
ye)
Downward
direction
Upward
direction
Average(Pue
)
A1
18.15
-
18.15
20.34
-
20.34
A
18.15
18.15
18.15
21.23
21.23
21.23
B
19.98
19.85
19.92
22.34
22.34
22.34
C
20.15
20.84
20.50
23.83
24.23
24.03
D
18.38
18.38
18.38
20.45
20.45
20.45
E
19.45
19.45
19.45
21.38
20.98
21.18
Table 2 shows the yield load and ultimate load in ANSYS analysis. The yield load for the specimen A1
is 18.15 k N and ultimate load is 20.34 k N under static loading. The yield load for the specimen A is 18.15
k N and ultimate load is 21.23 k N under dynamic loading. The yield load for the specimen B is 19.92 k N
and the ultimate load is 22.34 k N which is 9.75% and 5.22% more respectively than specimen A. The
yield load for the specimen C is 20.50 k N and the ultimate load is 24.03 k N which is 12.94% and 13.19%
more respectively than specimen A. The yield load for the specimen D is 18.38 k N and the ultimate load is
21.45 k N which is 1.26% and 15.16% more respectively than specimen A. The yield load for the specimen
E is 19.45 k N and the ultimate load is 22.03 k N which is 7.16% and 3.78% more respectively. It can be
seen in ANSYS analysis that the yield load carrying capacity and ultimate load carrying capacities of the
specimens are increasing by using the non-conventional cross diagonal bars and steel fibre at the beam
column joint. Also it can be seen that the results are better for the beam column joints with nonconventional diagonal bars extending in beam and column directions by .3H and .3B. The higher stiffness
in finite element models may be due to the no consideration of the micro cracks in concrete and bond slip
of the reinforcement. Thus considering the ultimate load carrying capacities from analytical studies it can
be observed that the maximum load carrying capacity is for the beam column joint with cross diagonal bars
at the joint and extending in beam and column direction .3B and .3H respectively. The average
displacement ductility of specimens A1,A,B,C,D&Eare 3.61,3.38,5.25,5.95,5.140 and 5.51 respectively. It
can be seen that the displacement ductility is more for the beam column joint with additional cross
diagonal bars and additional steel fibres. The percentage increase is 76.03% and 63.01%.The ductility is
more for the beam column joint with additional cross diagonal bars than steel fibre by 13.02%.
The below given graph, figure16 and 17 is for the load against downward /upward displacement of
specimens under static and transient loading. It can be seen that the displacement under yield load and for
ultimate load for the beam column joint under static loading, dynamic loading, with additional cross
diagonal bracing bars, with additional steel fibre is 3.45 mm, 12.45 mm,4.21mm,14.28mm, 4.11mm, 17.28
mm, 4.53mm , 19.28 mm,3.98 mm, 17.29mm and 3.95 mm, 18.67mm respectively. The displacement at
ultimate load increases when the additional cross diagonal bars and additional steel fibres are added at the
beam column joint. Also it can be seen that when the cross diagonal bars and fibres are added beyond the
beam column joint in column and beam direction upto .30 H and .3 B, the ultimate displacement obtained
is more than that obtained when the cross bars and fibres are at the joint alone. The effect of displacement
at yield load and at ultimate load with the additional cross diagonal bars is more than additional steel fibre
at the joint.
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25 Load-downward dispalcement graph
25
20
20
-A1
-A
-B
-C
-D
-E
10
15
Load in kN
Load in kN
15
Load-upward dispalcement graph
-A
-B
-C
-D
-E
10
5
5
0
0
5
10
15
0
20
0
5
10
Displacement in mm
15
20
25
30
Displacement in mm
Figure 16 Downward load-displacement curves
Figure 17 Upward load-displacement curves
Comparison of ultimate load in upward loading and downward loading for all specimens is shown in
figure 18 and 19. The ultimate load carrying capacities of specimens A1,A,B,C,D&E are 20.34 k N, 21.23
k N, 22.34 k N, 24.03 k N, 21.45 k N and 22.03 k N respectively. The ultimate load carrying capacity of
beam-column joint with cross diagonal bracing bars increases by 5.22% when comparing with normal
beam –column joint and when the cross bracing bars are extended in beam and column directions by .3 B
and .3 H , the increase in ultimate load carrying capacity is 13.18% when comparing with normal beam
column joint. When steel fibre is added in the beam column joint in addition to normal bars, the ultimate
load carrying capacity is increased by 1.03% and when the steel fibres are extended in beam and column
directions by .3 B and .3 H, the increase in ultimate load carrying capacity is 3.76% when comparing with
normal beam column joint. Also it can be seen that cross bracing bars is added at the beam column joint in
addition to normal bars, the ultimate load carrying capacity increases by 9.41% than that of beam column
joint with steel fibres.
Upward loading
25
23.5
23.23
Downward loading
24.23
23
24
22.34
22.5
23
22
22.34
21.5
22
21.23
Series1
20.5
Ultimate load in kN
20.45
Ultimate load in kN
21
20.98
21
21.38
21.23
20
20.45
20.34
Series1
20
19.5
19
18
19
18.5
A
B
C
D
E
A1
Specimen designation
A
B
C
D
E
Specimen designation
Figure 18 Upward loading
Figure 19 Downward loading
Comparison of average displacement ductility for all the specimens A1,A,B,C,D,E are given below in
the figure 20,21 and 22. The displacement ductility factor for specimens A,B,C,D,E are 3.38,4.41,5.95,5.14
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and 5.51 respectively. It can be seen that the displacement ductility is more for the beam column joint with
additional cross diagonal bars and additional steel fibres. The percentage increase is 76.03% and
63.01%.The ductility is more for the beam column joint with additional cross diagonal bars than steel fibre
by 13.02%.
6
Downward direction
5.27
5.2
4.72
5
Upward direction
9
4.34
7.64
8
3.61
3.39
Displacement ductility
Displacement ductility
4
3
Series1
2
1
0
A1
A
B
C
D
7
5.94
6
6.31
5.2
5
3.36
4
-
3
2
1
0
A
E
B
Specimen designation
C
D
E
Specimen designation
Figure 20 Ductility Downward direction
Figure 21 Ductility Upward direction
7
5.95
6
5.51
Displacemnet ductility
5.25
5.14
5
4
3.61
3.38
3
Series1
2
1
0
A1
A
B
C
D
E
Specimens
Specimens
Figure 22 Average displacement ductility
5. ENERGY DISSIPATION
With the models so far developed, the energy absorption capacity of different joints can be studied since
ductility is directly linked with energy absorption capacity of joints. The figure 23 and 24 below shows the
moment slope curves and cumulative energy absorption for the specimens A1,A,B,C,D and E respectively.
The area enclosed by the graph represents the energy dissipated by the specimens. It can be seen that the
energy dissipation is maximum for the beam column joint specimen with additional cross diagonal bars at
the joint and extending in beam and column directions by .3 B and .3 H in addition to normal
reinforcement. The beam column joint with additional diagonal confining bars, the energy dissipated is
found more than that of the beam column joint with normal bars. Also it can be found that the beam
column joint with normal reinforcement A1 and A starts yielding much before than the additional bars and
fibres. The specimens B and C the moment at yielding point is more than the moment at yielding point of
the beam column joint with additional fibres for the specimens D and E. The energy dissipated by the
specimens A1,A, B,C,D and E are 280 kN-mm, 420 kN-mm, 455 kN-mm, 560 kN-mm, 475kN-mm and
512.50 kN-mm respectively. The increase in energy dissipated by the beam-column joint with diagonal
bars is 8.33% when comparing with the normal beam-column joint. The increase in energy dissipated by
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Cumulative energy dissipated in kN-mm
the beam column joint with steel fibre is 13.09% when comparing with the normal beam-column joint.
When comparing the energy dissipation capacity of beam –column joint with steel fibre and additionally
diagonally braced bars is 16.67% less. It can be seen that by extending the additional diagonal bars in the
beam-column joint in beam and column direction by .3B and .3H, the energy dissipation is increased by
7.69%. It can be seen that by extending the steel fibre in the beam-column joint in beam and column
direction by .3B and .3H, the energy dissipation is increased by 23.07%. The energy dissipation is
increasing with additional diagonal bars when comparing with steel fibre.
25
20
A1
15
A2
Moment in kN-m
B1
B2
10
C1
C2
5
0
0
0.02
0.04
0.06
0.08
600
560
512.5
500
475
455
420
400
300
280
Series1
200
100
0
0.1
A1
A
B
slope
C
D
E
Specimen
Figure 23 Moment - Slope curves
Figure 24 Cumulative energy dissipation
Table 3 Maximum bending/ shear stress
Loading conditions
Maximum shear
stress(MPa)
Maximum bending
stress(MPa)
Static
7.51
17.34
Dynamic
10.72
18.27
Diagonal bars
7.05
14.48
.3B
6.00
12.30
1% fiber
10.10
16.15
.3B
8.95
14.38
The above table -3 indicates the results of ANSYS 16 analysis for specimens the maximum principle
stress, maximum shear stress, under static loading, seismic loading, using normal reinforcement steel, steel
fibers, using diagonal cross bracing bars at the joint, for exterior beam-column joints. The maximum shear
stress obtained in static loading is 7.51 MPa whereas the maximum shear stress under dynamic loading is
10.72 MPa with a percentage increase of 42.74%. The maximum bending stress obtained in static loading
is 17.34 MPa whereas the maximum bending stress under dynamic loading is 18.27 MP with a percentage
increase of 5.36%.
Analytical study of exterior beam column joint with additional diagonal bars within the joint subjected
to static and seismic loading by nonlinear finite element analysis using ANSYS software for nonlinear
analysis of reinforced concrete structures were carried out by increasing the diagonal reinforcement in
beam directions and column directions .3B and .3H respectively. The maximum shear stress obtained
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under the same loading conditions in dynamic loading is 7.05 MPa. The maximum bending stress under
dynamic loading is 14.48 MPa. The maximum shear stress and maximum bending stress of beam column
joint with additional cross diagonal bars extending in beam and column directions by .3B and .3H are 6.00
MPa and 12.30 MPa. It can be seen that the bending stress and shear stress are decreasing by 15.05% and
14.89% respectively. From the analysis it can be seen that the effect of diagonal bars in exterior beam
column joint in reducing shear stress and bending stress at the joint under static and dynamic loading
conditions is effective when comparing with joint without cross diagonal bars. The additional bars
effectively increased the strength capacity at the joint vicinity as well as sufficient development of ductility
to the frame members under increasing lateral loading. The joint was fully restrained at the column ends. It
was inferred from the analysis that as load increases displacement, minimum stress and maximum stress
also increases. Also the stiffness of the structure changes the displacement, minimum stress and maximum
stress changes with respect to loading. With the increase of ratio of bending moment of column to beam,
the plastic hinges are more likely to develop in the beam, and the ductility of the joint improves. Additional
diagonal bars prevented cracks at the edges of the joint interface between column and beam. Furthermore,
these joints have been proven to behave in a ductile manner as beams undergo plastic hinging earlier than
the columns. The orientation of additional cross diagonal bars added strength in favour of members they
were oriented to. That is, additional bars along beam added strength towards the beam ends and additional
bars along column added strength towards the column.
The performance of steel fibre reinforced exterior beam-column joints were compared with that of
conventional joints. Results showed that using steel fibre reinforced concrete (SFRC) within beam-column
can significantly enhance the shear resistance capacity of joints.It can be seen that the effect of steel fiber
in exterior beam column joint in reducing shear stress and bending stress at the joint under static and
dynamic loading conditions is effective when comparing with joint with normal reinforcement steel and
with diagonal bars. The maximum shear stress obtained under dynamic loading condition is 10.10 MPa
whereas the maximum bending stress is 16.15MPa. The maximum bending stress obtained under the same
loading conditions in dynamic loading with steel fiber extending in beam and column directions by .3B
and .3 H is 14.38MPa whereas the maximum shear stress is 8.95 MPa. The analysis results also showed
that using additional steel fibre reinforcement is an effective method to reduce the lateral reinforcement in
the beam plastic hinge region. The decrease in bending stress by extending the fibre in beam and column
directions is 10.95% and 10.99%.
It is generally accepted that addition of steel fibres significantly increases tensile toughness and
ductility, also slightly enhances the compressive strength. The benefits of using steel fibres become
apparent after concrete cracking because the tensile stress is then redistributed to fibres. The results
showed that using steel fibres can significantly increase the joint shear strength and also the shear stress
corresponding to the first crack.
6. EXPERIMENTAL WORK
•
Five samples casted and tested in laboratory as given below A-Normal (as per IS 456- 2000)
•
B-With additional diagonal bars at the joint
•
C-With additional diagonal bars at the joint and extending in beam ( .3B) & column(.3H)
•
D-With additional fibre at the joint
•
E-With additional fibre at the joint and extending in beam (.3B) & column (.3H)
•
Specimen size(T Shape) - Column size- 1000 mm x 175 mm x 150 mm. Beam size- 600 mm x 175 mm x
150 mm.
•
The material properties of steel fibre used are DRAMIX ® 3D with tensile strength 1225 N/mm2, Young’s
modulus 210000 N/mm2, length 60 mm, aspect ratio 80 and diameter is 0.75 mm.
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Cross Bracing Bars and Steel Fibres for Improving the Joint Ductility
Figure 25 Casted specimen ready for testing
Figure 26 Test set up
Figure 28 Crack patterns.
Figure 27 Testing progress
Table 4 Displacement ductility of specimen tested in laboratory
Displacement (mm)
specimen
yield
ultimate
Displacement ductility
Average
displacement
ductility
Downward
direction
Upward
direction
Downward
direction
Upward
direction
Downward
direction
Upward
direction
A
4.70
4.60
16.50
16.00
3.50
3.50
3.50
B
4.17
3.70
21.50
19.50
5.15
5.25
5.20
C
3.40
4.40
15.00
33.00
4.40
7.50
5.95
D
3.70
3.75
17.29
22.45
4.30
5.90
5.10
E
4.10
4.13
18.67
24.78
4.50
6.00
5.25
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The displacement ductility of all the specimens tested in laboratory is presented in table 4. It can be
seen that the displacement ductility is more for the beam column joint with additional cross diagonal bars
and additional steel fibres. The percentage increase is 70% and 50%.The ductility increment is more for the
beam column joint with additional diagonal cross bars than with additional fibres by 20%. It can be seen
that the displacement ductility factor for beam column joint with additional cross bracing bars is 48.57%
more than that of normal beam column joints. Also it can be seen that the results are better for the beam
column joints with non-conventional diagonal bars extending on beam and column directions by .3H and
.3B. The ultimate upward displacement is greater than the downward displacement for all the specimens.
Table 5 Yield load and ultimate load of specimen tested in laboratory
Yield load (kN)
Ultimate load (kN)
Specimen
Downward
direction
Upward
direction
Average(P
ye)
Downward
direction
Upward
direction
Average(Pue
)
A
15.35
15.50
15.45
18.25
18.75
18.50
B
17.80
18.10
18.45
21.50
22.50
22.00
C
22.50
23.75
23.12
25.25
26.75
26.00
D
18.38
18.75
18.48
20.50
21.50
21.00
E
19.00
19.25
19.12
22.00
24.00
23.00
Average displacement ductility
Experiment results
30
26
25
23
22
20
21
18.5
Ultimate load in kN
15
Series1
10
5
7
Experiment- displacement ductility
5.95
6
5.2
5.1
5.25
5
4
3.5
Series1
3
2
1
0
0
A
B
C
Specimens
D
E
Figure 29 Ultimate load of specimens
A
B
C
D
E
Figure 30 Average displacement ductility of specimens
Testing results shows the yield load for the specimen A is 15.45 k N and ultimate load is 18.50 k N
under dynamic loading. The yield load for the specimen B is 18.45 k N and the ultimate load is 22.00 k N
which is 19.41% and 18.91% more respectively than specimen A. The yield load for the specimen C is
23.12 k N and the ultimate load is 26.00 k N which is 49.64% and 40.54% more respectively than
specimen A. The yield load for the specimen D is 18.48 k N and the ultimate load is 21.00 k N which is
19.43% and 13.51% more respectively than specimen A. The yield load for the specimen E is 19.12 k N
and the ultimate load is 23.00 k N which is 23.75% and 24.32% more respectively. It can be seen in
experimental results that the yield load carrying capacity and ultimate load carrying capacities of the
specimens are increasing by using the non-conventional cross diagonal bars and steel fibre at the beam
column joint. Also it can be seen that the results are better for the beam column joints with nonconventional diagonal bars extending in beam and column directions by .3H and .3B. Thus considering the
ultimate load carrying capacities from experimental studies it can be observed that the maximum load
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carrying capacity is for the beam column joint with cross diagonal bars at the joint and extending in beam
and column direction .3B and .3H respectively.
6.1. Energy Dissipation in Experimental Works Load –Displacement Hysteresis Loops
From the experimental works, the energy absorption capacity of different joints can be studied since
ductility is directly linked with energy absorption capacity of joints. The figure 23 and 24 below shows the
load –displacement hysteresis loops and cumulative energy absorption for the specimens A,B,C,D and E
respectively. The area enclosed by the graph represents the energy dissipated by the specimens. It can be
seen that the energy dissipation is maximum for the beam column joint specimen with additional cross
diagonal bars at the joint and extending in beam and column directions by .3 B and .3 H in addition to
normal reinforcement. The beam column joint with additional diagonal confining bars, the energy
dissipated is found more than that of the beam column joint with normal bars. Also it can be found that the
beam column joint with normal reinforcement A starts yielding much before than the additional bars and
fibres. The specimens B and C the moment at yielding point is more than the moment at yielding point of
the beam column joint with additional fibres for the specimens D and E. The energy dissipated by the
specimens A, B,C,D and E are 450 kN-mm, 475 kN-mm, 600 kN-mm, 525kN-mm and 550 kN-mm
respectively. The increase in energy dissipated by the beam-column joint with diagonal bars is 8.33%
when comparing with the normal beam-column joint. The increase in energy dissipated by the beam
column joint with steel fibre is 13.09% when comparing with the normal beam-column joint. When
comparing the energy dissipation capacity of beam –column joint with steel fibre and additionally
diagonally braced bars is 16.67% less. It can be seen that by extending the additional diagonal bars in the
beam-column joint in beam and column direction by .3B and .3H, the energy dissipation is increased by
7.69%. It can be seen that by extending the steel fibre in the beam-column joint in beam and column
direction by .3B and .3H, the energy dissipation is increased by 23.07%. The energy dissipation is
increasing with additional diagonal bars when comparing with steel fibre.
25
SPECIMEN-A
SPECIMEN-B
20
25
15
20
10
15
5
10
SAMPLE-A
0
-20
-15
-10
-5
-5
SAMPLE-B
0
5
0
5
10
15
20
-25
-20
-15
-10
-5
0
5
10
15
20
Series2
25
-5
25
-10
-10
-15
-15
-20
-20
-25
-25
Figure 31 Specimen as per-IS-456-2000
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Figure 32 Specimen with cross diagonal bars at joint
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SPECIMEN-C
SPECIMEN-D
30
25
20
LOAD IN kN
20
15
10
10
5
0
-30
-20
-10
0
10
20
SAMPLE-C
40
30
SAMPLE-D
0
-25
-20
-15
-10
-5
-5
0
5
10
15
20
25
-10
-10
-15
-20
-20
-30
-25
Figure 33 Specimen with cross diagonal bars extended Figure 34 Specimen with steel fibres at joint
700
20
10
0
-25
-20
-15
-10
-5
SAMPLE-E
0
5
10
15
20
25
30
-10
-20
cumulative energy dissipatedkN-mm
SPECIMEN-E
30
Expeirment- cumulative enery dissipation
600
600
525
500
450
550
475
400
Series1
300
200
100
0
A
-30
B
C
specimen
D
E
Figure 35 Specimen with steel fibres extended Figure 36 Experiment- Cumulative energy dissipation
Table 6 Comparison of energy dissipation Analysis vs Experimental
Specimen
Energy dissipation kN-mm)Analysis
Energy dissipation(kNmm)-Experimental
% increase energy dissipation
A
420
450
-
B
455
475
5.55
C
560
600
33.33
D
475
525
16.67
E
521.5
550
22.22
The beam column joint with additional diagonal confining bars, the energy dissipated is found more
than that of the beam column joint with normal bars with increase of 25%. The beam-column joint with
additional steel fibres, the energy dissipation is found less than that of joint with cross diagonal bars by
9.10%. The increase in energy dissipated by the beam-column joint with diagonal bars extended in beamcolumn direction is more that when comparing with the normal beam-column joint with cross diagonal
bars at the joint by 26.31%. The increase in energy dissipated by the beam column joint with steel fibre is
22.22% when comparing with the normal beam-column joint.
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Table 7 Comparison of ultimate load- Analysis vs experimental
Specimen
Ultimate load (kN)Analysis
Ultimate load (kN)Experimental
% variation
A
21.23
18.50
12.85
B
22.34
22.00
1.52
C
24.03
26.00
8.19
D
20.45
21.00
2.68
E
21.18
23.00
8.59
The ultimate load in analysis for the specimen A is 21.23 k N and the ultimate load in testing is 18.50 k
N which is 12.85% variation. The ultimate load in analysis for the specimen B is 22.34 k N and the
ultimate load in testing is 22 k N which is 1.52% variation. The ultimate load in analysis for the specimen
C is 24.03 k N and the ultimate load in testing is 26 k N which is 8.19% variation. The ultimate load in
analysis for the specimen D is 20.45 k N and the ultimate load in testing is 21 k N which is 2.68%
variation. The ultimate load in analysis for the specimen E is 21.18 k N and the ultimate load in testing is
23 k N which is 8.59% variation. It can be seen in ANSYS analysis that the yield load carrying capacity
and ultimate load carrying capacities of the specimens are increasing by using the non-conventional cross
diagonal bars and steel fibre at the beam column joint.
Table 8 Comparison of ultimate load and increase in load carrying capacity
Specimen
Ultimate load (kN)Analysis
Ultimate load (kN)Experimental
% increase in load
A
21.23
18.50
-
B
22.34
22.00
18.91
C
24.03
26.00
40.54
D
20.45
21.00
13.51
E
21.18
23.00
24.32
The ultimate load carrying capacity of beam-column joint with cross diagonal bracing bars increases by
18.91% when comparing with normal beam –column joint and when the cross bracing bars are extended in
beam and column directions by .3 B and .3 H , the increase in ultimate load carrying capacity is 40.34%
when comparing with normal beam column joint. The ultimate load carrying capacity of beam-column
joint with fibres increases by 13.51% when comparing with normal beam –column joint and when the
fibres are extended in beam and column directions by .3 B and .3 H, the increase in ultimate load carrying
capacity is 24.32% when comparing with normal beam column joint.
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Table 9 Comparison of ductility factor and increase in ductility
Specimen
Average displacement
ductility
Increase in displacement
ductility with normal
specimen
% increase
A
3.50
-
-
B
5.20
1.70
48.57
C
5.95
2.45
70.00
D
5.10
1.60
45.71
E
5.25
1.75
50.00
It can be seen that the displacement ductility factor for beam column joint with additional cross bracing
bars is 48.57% more than that of normal beam column joints. The cross bracing bars extending in beam
and column direction by .3B and .3H, the ductility factor increases by 70%than that of beam column joints
with bars at the joint. Beam column joints with addition of steel fibre, the ductility factor increases by
45.71% and when the fibres are extended in beam and column directions by .3B and .3H, the ductility
factor increases by 50%. It can be seen that the ductility factor is more for the beam column joints with
cross bracing bars by 20% than steel fibres. The cross bracing bars extending in beam and column
direction by .3B and .3H, the ductility factor increases by 21.43%than that of beam column joints with bars
at the joint.
7. CONCLUSIONS
In this paper performance of exterior beam column joints with non-conventional reinforcement detailing
and steel fibres were examined analytically using ANSYS 16 modeling and analysis and experimentally
tested specimens under static loading, seismic loading, using normal reinforcement steel, steel fibers, using
cross diagonal bars at the joint, diagonal bars and fibers at varying depths and heights in beam and column
directions are carrying out to find out various factors affecting the failure of joints under different loading
conditions. The exterior beam-column joints are studied with different parameters like i.e. Maximum
principle stress, Maximum shear stress, Displacement, rotations, yield load, ultimate load, displacement
ductility and energy absorption capacity. Specimens were casted and tested at laboratory to compare the
results obtained the in analysis and experiment. It is found that the results of ANSYS analysis and
experiments are matching very well with marginal variations as tabulated. Specimens were casted and
tested at laboratory to compare the results obtained the in analysis and experiment. It is found that the
results of ANSYS analysis and experiments are matching very well with marginal variations as tabulated.
Additional cross diagonal bars, steel fibres at the joint along with lateral reinforcement prevented cracks at
the edges of the joint interface between column and beam. The additional cross diagonal bars and steel
fibres extension in the beam and column directions analysis results shows increase the ductility of the joint
, yield load and ultimate load carrying capacity and increased energy absorption capacity under higher
loading conditions. The orientation of additional diagonal bars added strength in favour of members they
were oriented to. Additional bars along beam added strength towards the beam ends and additional bars
along column added strength towards the column. The performance of steel fibre reinforced exterior beamcolumn joints were compared with that of conventional joints. Results showed that using steel fibre
reinforced concrete (SFRC) within beam-column joints can significantly enhance the shear resistance
capacity, displacement ductility and energy absorption capacity of joints. The analysis results also showed
that using steel fibre reinforcement is an effective method to reduce the lateral reinforcement in the beam
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plastic hinge region and can significantly increase the joint shear strength and also the shear stress
corresponding to the first crack.
8. ACKNOWLEDGEMENT
ANSYS 16 modeling and analysis of RCC exterior beam column joints under different loading conditions
and specimens were casted and tested at laboratory to compare the results obtained the in analysis with the
whole hearted help, support and directions of many people through their constructive criticisms in the
evaluation and preparation of this paper. The author takes this opportunity to appreciate the works done by
many researchers in this field. Thanks to all for extending the necessary support and guidance required to
complete this paper.
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