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.