dinh thi nhu thao punching shear behavior of flat …
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MINISTRY OF EDUCATION AND TRAINING
THE UNIVERSITY OF DANANG
DINH THI NHU THAO
PUNCHING SHEAR BEHAVIOR OF
FLAT SLAB - CONCRETE FILLED TUBULAR
(CFT) COLUMN CONNECTIONS
MAJOR: MECHANICAL ENGINEERING
CODE: 62.52.01.01
DOCTORAL THESIS SUMMARY
Danang – 2019
The work was finished at DANANG UNIVERSITY
Science Advisor:
1. Assoc. Prof. Ngo Huu Cuong, Ph.D
2. Assoc. Prof. Truong Hoai Chinh, Ph.D
Reviewer 1: Prof. Pham van Hoi, Ph.D
Reviewer 2: Assoc. Prof. Truong Tich Thien, Ph.D
Reviewer 3: Tran Dinh Quang, Ph.D
This dissertation is defended before The Assessment Committee at
The University of Danang.
Time: 8 h 30
Day: 15 / 06 / 2019
The dissertation is available at:
- National Library of Vietnam
- Communication & Learning Information Resource Center -
University of Da Nang.
1
INTRODUCTION
1. The significance of this research
In the past decades, Steel-Concrete composite structures have been
used more and more widely in civil and industrial buildings in many
countries all over the world because of the outstanding advantages of the
combination between concrete and steel materials in both structural and
constructional aspect. The buildings using a combination of this structural
solution illustrated high strength, stiffness and toughness, which satisfies
the utility, economic efficiency, aesthetics as well as fire resistance
compared to traditional steel structure.
In high-rise buildings, the height of the floor, the size of column and
span of the structural components are important factors affecting the
economic efficiency and utility of the buildings. Therefore, the demand for
a new structure which can reduce the height of the floor, the size of the
column and increase the structural span, shorten the construction time and
save construction costs is a very necessary issue. The structural systems
using Concrete Filled Steel Tube (CFT) column and reinforced concrete
flat slab are relatively new structure in accordance with the above criteria,
and they are expected to be widely applied in the world in near future.
However, the effective connections between CFT column and flat slabs
and their punching shear behaviors, which are vital factors in ensuring the
strength of the structural system, have not yet been investigated adequately
and are attracting much attention from numerous researchers.
This thesis proposes a new type of the connection between the RC
flat slab and the CFT column with simplified details, easy fabrication and
suitable construction conditions in Vietnam. Through calculations and
preliminary simulations, the size and composition of the CFT column-flat
slab connections will be proposed. The shear resistant and punching shear
behavior of full-scale specimens will be investigated through empirical
experiment. In addition, the analytical model will be simulated by using
three-dimensional finite element software (ABAQUS) and the reliability
of the simulation technique will be verified by comparison with the
experimental results.
2. Objectives of the study
2
- The thesis proposed a unique connection between the reinforced
concrete flat slab and CFT columns with simplified details, easy
fabrication and suitable for Vietnam construction conditions.
- Investigate the punching shear behavior of RC flat slab-interior
CFT column connection by experiments and numerical analysis.
- Propose an analytical model to predict the punching shear capacity
of RC flat slab-interior CFT column connection.
3. Scientific and empirical significance of research
Scientific significance
In Vietnam, the application of CFT columns in buildings is
relatively new and not yet popular. The results obtained from the
experiments and simulations in this study will contribute to the new
arguments and knowledge as well as useful data for future research in this
field.
Empirical significance
Presently, the connections between the reinforced concrete flat slabs
and the CFT columns have been proposed and investigated by numerous
authors to investigate the structural behavior and efficiency for practical
application. The proposal of a new the connection between the reinforced
concrete flat slabs and the CFT columns, which contains a simplified detail
and is efficient as well as suitable for the construction conditions in
Vietnam, will be the prerequisite for further research on other types of
connections to develop structural solution for CFT column - reinforced
concrete flat slab in construction. In particular, the introduction of a
numerical model to predict the load-carrying-capacity of the connection in
accordance with the experimental results is essential to obtain reliable
results in the structural design of this type of connections in practice
without any costly and time-consuming experiments.
4. Content of Research
- Provide an overview of the research project.
- Propose a unique connection between the reinforced concrete flat
slabs and the CFT column.
- Full scale test specimen fabrication.
3
- Test setup and Experimental program.
- Process, analyze data and evaluate the results.
- Simulate the behavior of the connections by using ABAQUS
three-dimensional finite element software with considering the nonlinear
geometrical effects and nonlinear material effects.
- Verify the reliability of the simulation technique by comparing
the test results with the experimental results.
- Draw the conclusions and recommendations.
5. Research Methodology
Use experimental research methods in combination with numerical
simulation by using ABAQUS three-dimensional finite element software
6. Object and scope of the study
Research subjects:
Experimental investigation and simulation of the behavior of CFT column-
reinforced concrete flat slab connections subjected to punching shear load.
Research scope:
- Conventional Flat slab system, no pre-stress effect, no-hole near
the connection, interior CFT column
- Not consider the combination action of moment cause by
horizontal loading and the column axis;
- Only use increased static load, not cyclic or dynamic load.
7. The composition of the thesis
The thesis contains 125 A4 pages with following composition:
Introduction.
Chapter 1: Overview of CFT column-reinforced concrete flat slab
connections.
Chapter 2: Experimental Program of CFT column-flat slab connections
Chapter 3: Investigation the Behavior of CFT Colum-RC Flat Slab
Connections by Numerical Method.
Conclusion and development direction.
8. Contribution of the thesis
- The thesis proposed a unique connection between reinforced
concrete flat slab and CFT columns with simplified details, easy
fabrication and suitable for domestic construction conditions.
4
- Establish experimental procedures and conduct experiments to
investigate the punching shear behavior of the proposed RC flat slab-CFT
column connection.
- Simulate the behavior of the connection by using ABAQUS
three-dimensional finite element software and verify with the experimental
results.
- Establish a calculation process to predict the punching shear
capacity of proposed RC flat slab-interior CFT column connection based
on Vietnam Standard TCVN 5574: 2012, Euro Code 2 and American
standard ACI 318-11.
CHAPTER 1: OVERVIEW OF CFT COLUMN-
REINFORCED CONCRETE FLAT SLAB CONNECTIONS
1.1 Concrete Filled Tubular (CFT) Columns
1.2 Reinforced Concrete Flat Slabs
1.3 The Connections between Reinforced Concrete Flat Slabs and CFT
Columns
1.3.1 The Study of Satoh and Shimazaki (2004)
Satoh and Shimazaki (2004) [37] experimentally investigated the
punching shear behavior of square CFT column- RC flat slab joints
Figure 1.22 and Figure 1.23: The Connection Details and
Experimental Setups of Satoh and Shimazaki
1.3.2 The Study of Su and Tian (2010)
Su and Tian (2010) [40] investigated the punching shear behavior of
interior circular CFT column – RC Flat slab connection subjected to
earthquake load. The test results showed this type of connection can sustain
Diaphragm
Connection Plate
5
a larger value of drift ratio than the conventional column-reinforced
concrete flat slab connections.
1.3.3 The Study of Yan (2011)
Yan (2011) [44] has proposed two types of CFT column- flat slab
connections. The interior CFT column contains I-type shear reinforcement
detail (type 1) and box type shear reinforcement detail (type 2). Two
specimens were tested under punching shear until failure. The
experimental results show that the ultimate load carrying capacity of the
type-1 specimen was 417 kN while the type-2 one was 569 kN
Hinh 1.32: The type-1 specimen of
Yan
Hinh 1.34: The type-2 specimen of
Yan
1.3.4 The Study of Kim et. al (2014)
Kim et al. (2014) [23] proposed a rigid shear resistance details for
CFT column-RC flat slab connections by using steel shearheads. The test
results showed that the punching shear capacity of the connections using
steel shearheads was higher than that of conventional details.
1.3.5 Local researchers
1.4 Pros and Cons of existing CFT column-flat slab connections
1.4.1 Pros: Ensure the require strength and ductility
1.4.2 Cons: The connections proposed by Satoh and Shimazak, Yan, and
Kim et al. have complicated details and were embedded in slab causing a
difficulty construction and installation of steel reinforcement. Moreover,
the forces were transmited from the Slabs to the CFT columns only through
steel tubular shell by shear reinforcement details, not through the concrete
core.
1.5 Punching shear capacity of RC Column-Flat Slab Connection in
existing Building Design Code
6
1.5.1 Vietnam Building Code 5574:2012
1.5.2 EC-2 Building Code
1.5.3 ACI 318-11 Building Code
1.6 Conclusions
Chapter 1 presented the advantages of the CFT columns, the
reinforced concrete flat slabs as well as the CFT column-RC flat slabs
connection and the overview of this type of components . Through that, the
thesis also suggested the necessity of proposing a new connection between
reinforced concrete flat slabs and the CFT column and following by the
empirical research and simulating research to clarify the behavior and the
effectiveness of the proposed connection.
CHAPTER 2. EXPERIMENTAL PROGRAM OF CFT
COLUMN-FLAT SLAB CONNECTIONS
2.1 Experimental specimens
2.1.1 Introduction
The proposed connection is denoted as S-02-M-V and the
conventional RC column-flat slab connection with the same column
diameter and slab thickness is denoted as S-C-V.
2.1.2 Characteristic and details of proposed connections
2.1.2.2 The details of proposed connection
The details of proposed connection include (Figure 2.1 and Figure 2.2):
Figure 2.1 and Figure 2.2: The details of connection
2.1.2.2 Pros and Cons of proposed CFT column-flat slab connections
✓ Pros
650
400 125125
8
120
18
0
8
120
18
0
880
25
20
20
20
20
155
20
100
Stiffener detail
Steel column with
D=400mm
Steel plate with
the thickness of
16mm
155
80
20
25
20
20
20
20
155
20
100
180
400
16
7
− Steel reinforcement has a continuous detail.
− The stiffener and the supporter system transfer the vertical loads from
flat slab system to both steel tubular shell and concrete core and
increase the integrity of the connections.
− Moreover, because the stiffener and the supporter system are located
beneath the slab, the installation of longitudinal reinforcement is as
convenient as conventional RC flat-slab system.
✓ Cons
Because the stiffener and the supporter system are located beneath
the slab, aesthetics is not guaranteed.
2.1.3 Geometric characteristics and details of specimens
2.1.3.1 S-C-V specimen
Figure 2.3: The layout
of upper longitudinal
reinforcement of S-C-V
Figure 2.4: The layout
of lower longitudinal
reinforcement of S-C-V
Figure 2.5: A-A Section of S-C-V
2.1.3.2 S-02-M-V specimen
Figure 2.6: The layout of
upper longitudinal
reinforcement of -02-M-V
Figure 2.7: The layout of
lower longitudinal
reinforcement of -02-M-V
Figure 2.8: A-A Section
of -02-M-V
2.1.4 Experimental setup
– The experimental process is divided into 2 stages as follows:
A A
2500
8
120
180
21-d14a120 = 2400 5050
2500
21-d
14
a120 =
2400
50
50
120
18
0
2500
11-d14a240 = 2400 5050
2500
11-d
14
a24
0 =
2400
50
50
A A
21-d14a120 = 2400 5050
25
00
21
-d1
4a1
20
= 2
40
05
05
0
A A
2500
20
09
00
20
0
1050 400 10502500
d14a240
8d16
d6a150
d14a120
80
155
100
180
40020
440
200
2500
21-d14a120 = 2400 5050
200
20
2380
A A
2500
11
-d1
4a2
40 =
2400
50
50
2500
11-d14a240 = 2400 5050
8
Figure 2.10: Stage 1- The connection
is subjected to increasing cyclic load
up to drift ratio of H/140
Figure 2.11: Stage 2- The connection is
subjected to vertical load until failure
due to punching shear
2.2 Experimental apparatus
2.2.1 Loading frame
2.2.2 LVDT system, straingauge and measuring devices
2.3 Experimental process and test result analysis
2.3.1 Material
2.3.1.1 Concrete
a) Comperessive strength of
specimens, fcm
b) Splitting tensile strength of specimens, fsp
Figure 2.13: Comperessive Splitting tensile strength tests
The average compressive strength of specimes, fcm, was 40.4 MPa
and the average splitting tensile strength of specimens fctm = 0.9fsp = 3.16
MPa. The test results were illustrated in Table 2.4 và Table 2.5.
2.3.1.2 Steel plate
Steel plates and steel cover of the CFT of S-02-M-V specimen used
Q345B steel. Tensile tests showed that the plate has the yield strengh of
351 MPa, and the ultimate strength of 489 MPa.
Cyclic load
Gap
Connection subjected to
pre-
displacement
9
Figure 2.14: Stress-strain relationship of steel plate
2.3.1.3 Longitudinal reinforcement
Longitudinal reinforcement used in this experiment is Vietnamese-
Japanese steel with the diameter of 14mm- SD390. Tensile tests showed
that the longitudinal reinforcement has the yield strengh of 532.5 MPa, and
the ultimate strength of 614.0 MPa.
Figure 2.15: Stress-strain relationship of longitudinal reinforcement 14
2.3.2 Installation of LVDTs and strain gauges
2.3.2.1 The LVDTs installation of S-C-V and S-02-M-V:
The LVDTs were attached above the slab after the specimen has
been mounted into the loading system and denoted as D1, D2, D3, D4, D5,
D6 (Figure 2.16 and Figure 2.17).
Figure 2.16: The layout of LVDTs
of S-C-V and S-02-M-V
Figure 2.17: Elevation of LVDTs
of S-C-V and S-02-M-V
H
2500
100
200
200
1050
1050
1050 1050
2500
1050 1050
2500
200 200
200 200
50 475
D2 D4
50475
D1D3
D5
50
D6
475
D3A
100
D1A
100100
100
100
100
100
D4A
D2A
D6 D5
D4A D2A
20
20
160
200
400200 850 200850
2500
D3D1
D3A
50 200 50200475100100 100 100
400
D1D3
H
D2 D4
D3A D1A
50
20
20
160
200
200 850 200850
2500
D5
D2A
200 50200475100100 100 100475
0
100
200
300
400
500
0 0,02 0,04 0,06 0,08 0,1 0,12 0,14
Str
ess
(M
Pa
)
Strain
0100200300400500600700
0 0,05 0,1 0,15 0,2
Str
ess
(N
/mm
2)
Strain
10
45°
A B
S1S3 S4S2
S5
S6
d = 184d = 184
d =
184
d =
184
C1 C2
C3
C4
C5
S2
400
S1S3 S4S2S2 d = 184d = 184
C1 C2
2.3.2.2 The strain gauge installation of S-C-V and S-02-M-V
The steel strain gauges were denoted as S1, S2, S3, S4, S5, S6 (Figure 2.18
and Figure 2.20). The concrete strain gauges were denoted as C1, C2, C3,
C3, C5 (Figure 2.5 và Figure 2.6).
Figure 2.18: Strain gauge installation of the upper layer of longitudinal
reinforcement (S-C-V specimen)
Figure 2.19: Strain gauge installation of concete (S-C-V specimen)
Figure2.20: The concrete strain gauge and upper layer steel strain gauge
S-02-M-V
2.3.3 Experimental process
2.3.3.1 Specimen casting
Figure 2.21. Formwork and reinforcement
installation of S-C-V
Figure 2.22: Concrete pouring
of S-C-V
Figure 2.23: Formwork and reinforcement installation of
S-02-M-V
Figure 2.24: Concrete pouring
of S-02-M-V
2.3.3.2 Transpostation, assembly and installation of specimen
11
Hinh 2.25: Installation of S-C-V Hinh 2.26: Installation of S-02-M-V
2.3.3.3 Load cell installation
Figure 2.27: Load cell erection for S-C-V and S-02-M-V
2.3.3.4 Measurement device installation
Figure 2.28: LVDT
installation for S-C-V
Figure 2.29: LVDT
installation for S-02-M-V
Figure 2.30: Steel and Concrete strain gauge installation for S-C-V and S-02-
M-V
12
Figure 2.31: The connections between the straingauges and the data logger
2.3.4 Experimental process and test results of S-C-V
2.3.4.1 Experimental process
The initial load was about 5% of the total calculated failed force,
about 30 kN / load segment.
2.3.4.2 Test results of S-C-V
Punching shear force: 827.3 kN
Figure 2.32: Force-Displacement
curve of S-C-V
Hinh 2.33: Force-strain curve of
longitudinal reinforcement of S-C-V
2.3.4.3 Punching cone characteristics of S-C-V
The test esults showed that the slab was damaged totally due to the
punching shear force. The value of punching shear force was recorded at
827.3 kN (Figure 2.36).
Hinh 2.35: Force-strain curve for
concrete of S-C-V
Hinh 2.36: The shape of punching
cone of S-C-V
0100200300400500600700800900
0 4 8 12 16 20 24
Forc
e (k
N)
Displacement(mm)
Thực nghiệm-D1
Thực nghiệm-D2
Thực nghiệm-D3
Thực nghiệm-D4
0100200300400500600700800900
0 0,01 0,02 0,03 0,04
Forc
e (k
N)
Strain
Thực nghiệm-S1
Thực nghiệm-S2
0100200300400500600700800900
-0,0015 -0,001 -0,0005 0
Lự
c (k
N)
Biến dạng
Thực nghiệm C1
Thực nghiệm C2
Thực nghiệm C3
Thực nghiệm C4
13
01020304050607080
0 4 8 12 16 20
Forc
e (k
N)
Horizontal displacement (mm)
0100200300400500600700800900
10001100
0 3 6 9 12 15 18 21 24 27
Forc
e (k
N)
Displacement (mm)
Chuyển vị D1Chuyển vị D2Chuyển vị D3Chuyển vị D4Chuyển vị D5Chuyển vị D6
2.3.5 Experimental process and test results of S-02-M-V
2.3.5.1 Stage 1
The horizontal force was loaded by using a hydraulic actuator with a
displacement-controlled method. The maximum load with respect to
17mm displacement was 74 kN.
Figure 2.38: Force-Horizontal displacement at column head
2.3.5.2 Stage 2
The CFT column-RC flat slab was subjected to vertical load until failure
and the ultimate punching shear load reached 1024.00 kN.
Figure 2.39: Force-displacement
relationship of S-02-M-V
Figure 2.40: Force-strain relationship of
steel re-bar of S-02-M-V
Figure 2.41: Force-strain curve for
concrete of S-02-M-V
Figure 2.42: The shape of
punching cone of S-02-M-V
0100200300400500600700800900
10001100
-0,003 -0,002 -0,001 0 0,001
Forc
e (k
N)
Strain
Biến dạng C1
Biến dạng C2
Biến dạng C3
Biến dạng C4
0100200300400500600700800900
10001100
0 0,005 0,01 0,015 0,02
Forc
e (k
N)
Strain
Biến dạng S1Biến dạng S2Biến dạng S3Biến dạng S4Biến dạng S5Biến dạng S6
14
2.3.5.4 Punching cone characteristics of S-02-M-V
Stage 1: Horizontal displacement at column head reached 17 mm
with respect to a Force of 74 kN, there is no cracks appeared on the surface
of slab.
Stage 2: The test results showed that the structural system was
destructive by punching shear. The ultimate punching shear load reached
1024.00 kN (Figure 2.42).
2.4 Conclusions
Chapter 2 presents the proposed flat concrete joint - reinforced concrete
and reinforced concrete reinforced concrete floor - CFT column,
experimental results of concrete materials, flat steel and reinforced
concrete floor and real process. Determine the punctured behavior of the
sample SCV and sample S-02-MV. The results of the experiments are
shown in diagrams of the relationship between puncture force and
quantities such as displacement, stress, strain in concrete and
reinforcement of samples S-C-V and S-02-M-V. The shape of the puncture
tower and the force-bearing behavior are similar to those of other authors
in the world.
CHAPTER 3 INVESTIGATE THE BEHAVIOR OF CFT COLUM-
RC FLAT SLAB CONNECTIONS BY NUMERICAL METHOD
3.1 Introduction
3.2 Overview of ABAQUS Software
3.2.1 Components in ABAQUS
3.2.2 Types of components used in simulation
3.2.3 Concrete material model
3.2.3.1 Concrete material modeling in Compression
3.2.3.2 Concrete material modeling in Tension
3.2.3.3 Modeling of plastic behavior of Concrete material
3.2.3.4 Concept of yield surface in plastic model
3.2.4 Contact interaction between surfaces of the components
3.2.4.1 “Tie” interaction
3.2.4.2 “Embedded elements” interaction
3.2.4.3 “Coupling” interaction
15
3.2.4.4 “Hard contact” interaction
3.3 Numerical simulation method in this Study
3.3.1 Material modeling
Figure 3.16: Compressive stress-
strain curve
Figure 3.17: Tensile stress-crack width
curve
The typical tensile stress-strain curve of steel plates and steel rebars
(d=14mm) of S-C-V and S-02-M-V were illustrated in Figure 2.14 and
Figure 2.15
3.3.2 Punching shear behavior simulation of RC interior Flat slab-
column connection (S-C-V Specimen)
3.3.2.1 The components of S-C-V
Figure 3.18: Geometrical
modeling
Figure 3.19: Concrete material modeling
Figure 3.20: Steel
reinforcement modeling
Figure 3.21: Upper and lower support modeling
3.3.2.2 Contact interaction of S-C-V
Table 3.3: Contact interaction of S-C-V
Components Form of
interactions
Interacted
components
RC Flat slab Hard contact − Upper and lower
boundary steel-
support plate
Steel rebars d=14mm Embedded element − RC Flat slab
− RC Column
3.3.2.3 The boundary condition of S-C-V
0
10
20
30
40
50
0 0,001 0,002 0,003 0,004
Str
ess
(MP
a)
Strain
0
1
2
3
4
0 0,1 0,2 0,3 0,4
Str
ess
(MP
a)
Crack width (mm)
16
The boundary conditions used in simulation is similar to those in
experiment, the 4 upper and lower boundaries are pinned connections
u1=u2=u3=0 (Figure 3.24 and 3.25)
Figure 3.24: Simulation
for the boundary
condition of upper
surface in S-C-V
Figure 3.25 Simulation
for the boundary
condition of lower
surface in S-C-V
Figure 3.26: Meshing
for S-C-V
3.3.2.4 Creating meshes for S-C-V specimen
The size of meshes for concrete element, steel plate support element and
steel rebars is 50mm. The result was presented in Figure 3.26.
3.3.2.5 The comparison between the numerical simulation results and
experimental results (specimen S-C-V)
Figure 3.27: Force-displacement D1 curve
for S-C-V
Figure 3.29: Force-strain S1 curve
for S-C-V
3.3.2.6 The formation of cracks and punching cone in the simulation of S-
C-V
Along with the development of radial cracks, tangen cracks outside the
perimeter of the column are formed, then these tangent cracks are joined
together to form the punching cone at a rate of loading of 759.58 kN
(Figure 3.34).
0100200300400500600700800900
0 0,01 0,02 0,03 0,04
Forc
e (k
N)
Strain
Mô phỏng-S1
Thực nghiệm-S1
0
100
200
300
400
500
600
700
800
900
0 5 10 15 20 25
Forc
e (k
N)
Displacement (mm)
Mô phỏng-D1
Thực nghiệm-D1
17
a b
Figure 3.32: The first tangent cracks appear
in S-C-V
Figure 3.33: Cracks appear in the direction of the four corners of
the slab in S-C-V
Figure 3.34: Shape of punching cone in S-C-V
3.3.2.7 Conclusion
The results show that the punching shear force of the simulation is
8.19% lower than that of the experiment and this value observed in the case
of D1 displacement is 6.82% lower. The cracking loading and area of
punching cone in the simulation are also close to the experimental results.
3.3.3 Punching shear behavior simulation of interior RC Flat slab-CFT
column connection (S-02-M-V Specimen)
3.3.3.1 The components of S-02-M-V
Figure 3.35: Concrete material
modeling
Figure 3.36: Slab and column modeling
Figure 3.37: Steel rebar modeling
Figure 3.38: The modeling of stiffener, steel plate at column head and steel column in S-02-M-V
18
3.3.3.2 Contact interaction of S-02-M-V
Table 3.5: Contact interaction of S-02-M-V Components Form of interactions Interacted components
RC Flat slab Hard contact − Steel column − Steel-plate support
Concrete core in CFT column
Hard contact − Steel column − Stiffener
Steel column Hard contact − Concrete core − Flat slab
Steel column Tie − Steel-plate support − Stiffener
Stiffener Hard contact − Concrete core Stiffener Tie − Steel column
− Steel-plate support Steel plate-support Hard contact − Flat slab Steel rebar in slab d=14mm
Embedded element − Flat slab − Concrete core
3.3.3.3 The boundary condition of S-02-M-V
The boundary conditions used in simulation is similar to those in
experiment, the 4 upper and lower boundaries are pinned connections
u1=u2=u3=0 (Figure 3.43 and 3.44).
3.3.3.4 Creating meshes for S-02-M-V specimen
The size of meshes for concrete element, steel plate support element and
steel rebars is 50mm. The result was presented in Figure 3.45.
Figure 3.43: Simulation for the
boundary condition of upper surface
in S-02-M-V
Figure 3.45: Meshing for S-02-M-V
3.3.3.5 The comparison between the numerical simulation results and
experimental results (specimen S-02-M-V)
19
Stage 1:
The connection is subjected to increasing cyclic load up to drift ratio of H/140.
Figure 3.46: Deformed shape of
S-02-M-V with respect to 17 mm displacement at the column
head
Figure 3.47: Force-displacement at column head in S-02-M-V
Figure 3.48: Mises stress in slab with respect to 17 mm displacement at the
column head
Conclusion: During the simulation, the horizontal load does not cause
cracks in the Slab (Figure 3.48).
Stage 2
Applying the vertical load using displacement-controlled method until
completely failure.
Table 3.6: The comparison between the numerical simulation results and
experimental results (S-02-M-V)
Punching
shear
force
(kN)
Displacement
D1
(mm)
Displacement
D3
(mm)
S-02-M-V (experiment) 1024.00 23.43 17.56
S-02-M-V (simulation) 925.15 22.38 15.25
Coefficient of variation 9.65% 4.48% 13.15%
0102030405060708090
0 2 4 6 8 10 12 14 16 18
Forc
e (k
N)
Displacement at the top of
column(mm)
Thực nghiệm
Mô phỏng
20
Figure 3.49: Force-displacement D1 curve for S-02-M-V
Figure 3.50: Force-strain C1 curve for S-02-M-V
3.3.3.6 The formation of cracks and punching cone in the simulation of S-
02-M-V
Along with the development of radial cracks, tangen cracks outside the
perimeter of the column are formed, then these tangent cracks are joined
together to form the punching cone at a rate of loading of 943.65 kN
(Figure 3.56 and Figure 3.57).
Figure 3.54: The first tangent cracks appear in
S-02-M-V Figure 3.55: Cracks
appear in the direction of the four corners of the slab in
S-02-M-V
Figure 3.56: Shape of punching cone in S-02-M-V
0
100
200
300
400
500
600
700
800
900
1000
1100
0 3 6 9 12 15 18 21 24
Forc
e (k
N)
Displacement(mm)
Mô phỏng-D1
Thực nghiệm-D1
0
100
200
300
400
500
600
700
800
900
1000
1100
-0,003 -0,002 -0,001 0
Forc
e (k
N)
Strain
Thực nghiệm-C1
Mô phỏng-C1
21
Figure 3.57: Shape of punching cone in S-02-M-V by experiment and
numerical simulation
3.3.3.7 Conclusion
The experimental and numerical results of S-C-V and S-02-M-V
showed that the punching shear capacity of proposed connection S-02-M-
V is over 20% higher than that of S-C-V and the stiffness of S-02-M-V is
also higher than S-C-V (Figure 3.58).
22
Figure 3.58: Force-displacement relationship of S-C-V and S-02-M-V
Table 3.7: The comparison between the numerical simulation
results and experimental results of S-C-V and S-02-M-V
Punching shear
force (kN)
Displacement
D1
(mm)
Displacement
D3
(mm)
Exp. Simul. Exp. Simul. Exp. Simul.
S-C-V 827.3 759.58 20.65 19.24 14.27 13.56
S-02-M-V 1024 925.15 23.43 22.38 17.56 15.25
Coefficient
of
variation
23.78% 21.79% 13.46% 12.68% 23.06% 12.46%
The numerical simulation results are relatively close to the
experimental ones, but the initial slope of the "force-displacement" curve
or "force-strain" curve from the numerical analysis is greater than the
corresponding results in experiment. This indicates that the initial stiffness
of the connection subjected to punching shear force from the numerical
0
100
200
300
400
500
600
700
800
900
1000
1100
0 3 6 9 12 15 18 21 24 27
Forc
e (k
N)
Displacement (mm)
Mô phỏng-D1-SCV
Thực nghiệm-D1-SCV"
Mô phỏng-D1-S02MV
Thực nghiệm-D1-S02MV
23
analysis is greater than the corresponding results from the experimental
one. It is also possible to realize the similarity of the other studies
simulating the behavior of reinforce concrete components subjected to
shear force. This is due to the limited simulation-capacity of the concrete
model available in the library of ABQUS software and should be clarified
in future studies.
3.4 A calculation process to predict the punching shear capacity of
specimen S-02-M-V based on TCVN 5574: 2012, EC 2 and ACI 318-
11.
3.5 Conclusion
The simulation results are shown in diagrams of the relationship
between punching shear force and various mechanical factors such as
displacement, stress strain in concrete and steel reinforcement of
specimens S-C-V and S-02-M-V. The simulation results show that the
variation is in the range of 1.5-10.0%. The shape of punching cone in
numerical simulation using ABAQUS software is quite similar to the
experimental results.
CONCLUSION AND DEVELOPMENT DIRECTION
1. Conclusion
− The study proposes a unique connection between the reinforced
concrete flat slab and the CFT column with simplified details, easy
fabrication and incline the ability of punching shear than those from other
published studies.
− The research has designed the process and perform the study of
punching shear capability of the connection. Imitated of some
experimental models by specialized software – ABAQUS, the following
conclusions can be withdrawn: Experimental results demonstrate that the
value of the punching shear capacity of the proposed connection (P =
1024.00 kN) is 24% higher than that of conventinal RC column-flat slab
connection (P = 827.3 kN), which has the same cross-section and
24
longitudinal reinforcement ratio. This experiment indicated the
connection, which is proposed, is able to bear the force. These results
illustrated that the punching shear force, displacement and deformation are
different from experimental results with values less than 10%. This proves
that numerical models can be used as a method to predict the behavior of
RC column-flat slab connection and CFT column-flat slab connection.
− Based on Vietnamese Standard TCVN 5574: 2012, Euro Code
2 and American Standard ACI 318-11, the reseach has put forward how
the punching shear of the new connection can be caculated. The outcome
of the extreme punching shear capability for the brand new S-02-M-V
connection demonstrated that maximum punching shear force value by the
standards are all lower than the punching shear capability by the empirical
study of the connection. This shows that propose a calculation is suitable
and safe for the S-02-M-V connection.
2. Development orientation
- The research results of this topic can be developed to propose a
connection details and investigate by empirical and numerical method for
edge column and corner column.
- Based on the results of the thesis, it is possible to propose some more
CFT column-flat slab connections which have the advantage in creating an
optimal solution in the CFT column- flat slab connection design.
- The numerical simulation of the behavior of shear structural components,
especially the punching shear capacity, by using finite element software is
relatively complicated and not appropriate for the pre-failure stage of test
specimen due to the incomplete concrete material model. Thus, it is
necessary to investigate the additional model from various FE software, or
to develop an appropriate material model to obtain the expected numerical
results.
DECLARATION
Some of the work presented in this thesis has previously been
published in the following papers:
1. Dinh Thi Nhu Thao, Luu Thanh Binh, Tran Duy Phuong,
Nguyen Tan Phat, Doan Ngoc Tinh Nghiem, Truong Hoai Chinh,
Ngo Huu Cuong (2017), Nonlinear Analysis of Concrete-Filled
Steel Tube Members under Mechanical and Thermal Loadings,
Vietnam Journal of Construction, ISSN 0866-8762, 10-2017, pp
96-101.
2. Dinh Thi Nhu Thao, Luu Thanh Binh, Tran Duy Phuong,
Nguyen Van Hiep, Truong Hoai Chinh, Ngo Huu Cuong (2018),
Second-order inelastic analysis of concrete-filled stell tube
columns, Journal of science and technology in civil engineering,
ISSN 1859-2996, 02-2018, pp 18-23.
3. Dinh Thi Nhu Thao, Luu Thanh Binh, Truong Hoai Chinh, Ho
Huu Chinh, Ngo Huu Cuong (2018), The comparison of
punching shear design of interior reinforced concrete Flat slab-
column connections in accordance with Vietnam Building
Standard, American Standard (ACI) and Euro Code (EC),
Vietnam Journal of Construction, ISSN 0866-8762, 10-2018, pp
191-194.
4. Dinh Thi Nhu Thao, Luu Thanh Binh, Le Minh Hoang, Truong
Hoai Chinh, Nguyen Van Hiep, Ngo Huu Cuong (2018),
Experimental investigation and Numerical simulations of
Punching shear behavior of interior reinforced concrete Flat slab-
column connections, Vietnam Journal of Construction, ISSN
0866-8762, 01-2019, pp 145-150.