Volume 5, Issue 12, December – 2020 International Journal of Innovative Science and Research Technology

ISSN No:-2456-2165

Experimental and Numerical Investigation on the

Behavior of Composite Cold Formed Steel Columns
under Axial and Lateral Loads
Ahmed I. Saleh 1, Nabil S. Mahmoud2 ,Fikry A. Salem3, Mohamed Ghannam4
1
B. Sc., Demonstrator, Civil Engineering department, Delta University for Science and Technology
2
Prof., Structural Engineering Dept., Faculty of Engineering, Mansoura University
3
Assoc. Prof., Structural Engineering Dept., Faculty of Engineering, Mansoura University
4
Lecturer, Structural Engineering Dept., Faculty of Engineering, Mansoura University

Abstract:- Steel-concrete composite structures are used affected obviously by both the number and width of the
widely in the current construction of bridges and multi- stiffeners[5]. However, research on CFST columns under
story buildings. Experimental and numerical studies cyclic lateral loading is still missing, which demonstrates a
were conducted to investigate the behavior of composite requirement for additional exploration in this area [6].
cold formed steel columns under axial load only with
lack of experimental investigation on composite cold Cold-formed sections are produced at encompassing
formed steel columns under lateral loads. This paper temperature and thus experience plastic deformations
conducted to investigate experimentally and numerically causing strain hardening of the material[7]. CFS section
the behavior of composite cold formed steel columns expands the solidarity to weight proportion which expanded
under axial and lateral loads. Five specimens were tested the interest of applying CFS section in constructions with
to evaluate the failure modes, strains development and higher load[8,9]. One of the principle impediments of the CFS
load-deformation histories in the steel tube. Finite section is its high slenderness (Width to thickness ratio)
element (FE) models using ANSYS Workbench were which exposed the CFS section to be buckled mainly by one
developed and verified against experimental results. The or a blend of three primary modes: local, distortional and
verified FE will be used in future by the authors to study Global buckling[10]. Closed sections such as box-shaped
the influence of key parameters that control the behavior sections made by interfacing two channel areas tip to tip are
of composite cold forms steel columns, including cross regularly found in use in cold-formed steel structures due to
sections, fastener spacing, fastener length, yield strength their relatively large torsional rigidity[11].
of steel, on the load carrying capacity. It was observed
from the obtained results that composite column with There are a few sorts of stiffening methods available
sigma section show better behavior than C section for use in CFT. For instance, welding longitudinal stiffeners
because of the web and flange for the sigma section are on the inner surfaces of the steel tube[12], inserting shear
both stiffened. The embedded fasteners length of 50mm studs in the steel tube and what's more by utilizing either tie
enhanced load carrying by 13% compared to 30mm bars or restraining rods to fortify the plastic zones of the
length. CFTs[13]. The effect of longitudinal stiffeners on the
behavior of square CFT stub columns experimentally had
Keywords:- Composite Columns, Finite Element Model, been studied by Ge and Usami[14]. The test results
Cold Formed Steel, Axial Loads, Lateral Loads. demonstrated that the longitudinal stiffeners effectively
delay the local buckling of the tube, increase the sectional
I. INTRODUCTION capacity and improve the lateral confinement of the concrete
core.
Concrete filled steel tube (CFST) columns are favored
for many earthquake resistant structures, columns in high In the past several decades, CFST have been broadly
rise buildings, bridge piers subject to high strain rate from utilized in seismic regions, because of their incredible quake
traffic and railways decks[1]. The main advantage of opposing properties[15].
composite construction is to enhance the properties of
concrete and steel[2]. The use of the composite action In this study, a series of lateral load tests was
between steel and concrete provides better properties if conducted to investigate the behavior of composite cold
compared to their individual responses, such as structural formed steel columns with relatively thick wall of 4 mm.
strength, durability and ductility[3]. Anis Saggaff et.al[4], Three different column sections were considered, with
studied the composite action of a cold-formed steel section different shear connectors spacing. A model was also
with bolted shear connectors of 16mm diameter, which developed by finite element program ANSYS[16] and
yielded better strength and moment carrying capacity. utilized to give a numerical viewpoint of the behavior of the
Increasing the number of shear connectors increase the load Composite cold formed steel columns. The comparison
carrying capacity of the columns and the failure mode is

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ISSN No:-2456-2165
shows that the finite element program has a good agreement plates and connected together using fasteners bolts with a
with the experimental results. vertical fastener spacing of 100mm, embedded fastener
length of 30mm. and horizontal spacing between fastener of
II. EXPERIMENTAL PROGRAM 200mm. column B-1 with cross section of 2 C covered by 2
plates and connected together using fastener bolts with a
Test Specimens vertical fastener spacing of 200mm and horizontal fastener
Five composite cold formed steel columns. Two had spacing of 100mm, embedded fastener length of 30 mm.
sigma cold formed section and three had C section. All column B-2 with cross section of 2 C covered by 2 plates
columns were built up by assembling the steel sections and and connected together using fastener bolts with a vertical
connecting together using cover plates and fasteners bolts as fastener spacing of 200mm and horizontal fastener spacing
shown in Fig.1 to create a tube to fill with normal strength of 50mm, clear fastener length of 30mm. column B-3 with
concrete, which had a compressive strength (fcu) of 25 MPa cross section of 2 C covered by 2 plates and connected
after 28 days. The considered parameters were the column together using fastener bolts with a vertical fastener spacing
cross section, the vertical spacing between fasteners, the of 200mm and horizontal fastener spacing of 100mm,
horizontal spacing between fasteners, the length of fasteners embedded fastener length of 50mm.
were used. The details of the tested columns are shown in
Fig.1 and table 1. Material Properties
The concrete cube dimensions and test procedures
Geometry of Specimens according to the Egyptian Code of Practice for Concrete
The columns are classified into two groups; A and B, Design ECP 203-2017[17]. Three cubes with dimensions of
first group A consists of two columns with sigma section 150x150x150mm were used to calculate the average
and the second one B consists of three columns with C compressive strength of the concrete used for the composite
section. All columns had a height of 1600mm, column A-1 columns. The average results of the compressive strength
with cross section of 2 sigma covered by 2 plates and are (fcu) of 25 MPa after 28 days.
connected together using fasteners bolts with a vertical
fastener spacing of 100mm, clear fastener length of 30mm. Steel used is st37 with yield and ultimate strength of
and horizontal spacing between fastener of 160mm Fig.1. 240 and 360 MPa respectively according to the
Column A-2 with cross section of 2 sigma covered by 2 manufacturer's specifications.

Table 1 Dimensions of columns specimen

Horizontal Spacing between fasteners,
Vertical Spacing between fasteners, (mm)
Cross Section Area, mm2

Plate Dimensions, (mm)

Fasteners length, (mm)

(mm)
Height (L), mm

Cross Section

Width, (mm)
Column

Spacing (a)

Edge
(b)

A1 1600 2∑250×80×4 5036 2 pl 184×4 100 120 40 30 200

A2 1600 2∑250×80×4 5356 2 pl 224×4 100 160 40 30 240

B1 1600 2[ 300×90×4 5220 2 pl 284×4 200 100 50 30 300

B2 1600 2[ 300×90×4 5220 2 pl 284×4 200 50 50 30 300

B3 1600 2[ 300×90×4 5220 2 pl 284×4 200 100 50 50 300

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ISSN No:-2456-2165

Fig. 1 Details of tested Columns

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ISSN No:-2456-2165
Experimental Setup
The experimental work of this study was conducted at
University of Mansoura in the Heavy Structures Lab using
the steel frame shown in Fig. 2. the axial and lateral loads
test procedures start with fixing column specimens at the
machine frame base and tested under axial compression and
lateral cyclic load. The cyclic load was applied by using
Two-way digital hydraulic jack of 1000kN capacity at the
top of the composite column. The column base was fixed
and the column top was loaded. The strain gauges, the strain
indicator shown in Fig. 3. Electrical resistance of 6 mm
length strain was used to measure the strains at the critical
locations of the composite columns. Linear Variable
Differential Transformer (LVDT) and dial gauges were used
to measure the displacement at the top and mid-height of the
column as shown in Fig. 3.

Fig.3 LVDT and strain gauges

Test Procedure
Each composite column tested under axial
compression of 20kN and lateral cyclic load. The cyclic load
was applied by using Two-way digital hydraulic jack of
1000kN capacity at the top of the composite column. Fig.4
shows the lateral load applied to the composite columns.

Fig.2 Main Test machine

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ISSN No:-2456-2165

Fig.4 lateral load applied to the tested composite columns

III. Test Results and Discussion

Experimental Results
Max Top Displacement

 For composite columns group A

The maximum top displacement (MTD), of composite
columns with two cross sections are represented in table 2,
The MTD of column A2 is greater than column A1 by about
15% at yield. At failure, The MTD of column A2 is greater
than column A1 by about 10% and column. As shown in
Fig.5.

Fig.5 Recorded horizontal maximum top displacement at

yield and failure for group A

 For composite columns group B

The maximum top displacement (MTD), of composite
columns with one cross section represented in table 2, The
MTD of column B2 is greater than column B1 by about 68%
and 13% greater than B3 at yield. At failure The MTD of
column B3 is greater than column B2 by about 12% and
25% than column B1. As shown in Fig. 6

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Fig. 6 Recorded horizontal maximum top displacement at yield and failure for group B

Table 2 Recorded horizontal maximum top and mid displacement at failure and yield for group A, B.
Top Displacement, mm Mid Displacement, mm
Column
Failure Yield Failure Yield
A1 39.52 11.765 18.184 5.612
A2 43.53 13.599 21.265 6.487
B1 48.7 13.43 25.45 7.048
B2 54.54 22.55 28.363 10.841
B3 60.71 19.99 31.868 9.458

Hysteretic Curves of Lateral Load Versus Column of 39.52 and 43.53 mm. For the group B, the maximum
Displacement lateral loads carried by the composite columns B1, B2 and
Fig. 7 to 11 show the hysteretic curves of lateral load B3 were 160, 160 and 180 kN, respectively, at MTD of
versus top displacement of the composite column for all 48.7, 54.54, and 60.71 mm, respectively. Group A showed a
tested specimens. For the group A, the maximum lateral large value of lateral displacements compared to column
loads carried by the composite columns A1 and A2 were group B, this may be as a result of large column width of
160 and 180 kN respectively, these loads were at the MTD group B.

Fig. 7 Hysteretic loop of column A1

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Fig. 8 Hysteretic loop of column A2

Fig. 9 Hysteretic loop of column B1

Fig. 10 Hysteretic loop of column B2

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Fig.11 Hysteretic loop of column B3

Failure Mode
All tested composite columns representing plate buckling failure. Local buckling was observed in all tested columns at the
column base as shown in Fig. 12

Fig. 12 (A1,A2,B1,B2,B3) Failure shape of tested columns

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Finite Element Modelling
This section gives a description of the finite element
modelling which were used to understand the behavior of
the composite cold-formed steel columns under axial and
lateral loads. Finite Element modelling is getting significant
and mainstream in structural analysis regards to the precise
outcomes and less time and cash expending that can be
acquired from FE modelling. A finite element analysis was
conducted using ANSYS Workbench. The cross-section
dimensions shown in Fig. 1 were used to setup the finite
element models. The structural steel and concrete were
added in the engineering data and the material properties
was assigned as follow; For steel, yield strength fy = 240
MPa, Poisson's ratio v = 0.3, elastic modulus E = 20 × 105
MPa. And for concrete, fcu= 25 MPa, Poisson's ratio v = 0.2,
elastic modulus E = 2.35 × 104 MPa. The contact between
steel and concrete was indicated as frictional connection
with frictional coefficient of 0.2[18], and the contact
between fastener and surrounding elements such as steel
section, steel plates and concrete were indicated as bonded
connection. Solid 186 element was used to model the steel Fig. 13 ANSYS Geometry model column A1
sections, fasteners and fixation plates; the element is a
higher order 3-D 20-node solid element that exhibits Comparison with Finite Element Model Results
quadratic displacement behavior.The element is defined by This section compares the outcomes between the finite
20 nodes having three degrees of freedom per node: element model (FEM) and experimental (EXP) data which
translations in the nodal x, y, and z directions. While for the were collected from laboratory tests of the composite
concrete, the solid element Solid 65 which has eight nodes columns. The comparison is made for lateral load capacity
with three degrees of freedom at each node: translations in of all composite column table 3 presents the acquired
the nodal x, y, and z directions[19]. The final model is outcomes from the experimental data and were compared
shown in Fig. 13. with outcomes from the finite element model.

Table 3 Experimental vs Analysis results

Failure load, kN
Column Exp./Analysis
Experimental Analysis
A1 160 190.9 0.84
A2 180 216.4 0.83
B1 160 166.8 0.96
B2 160 170.2 0.94
B3 180 216.1 0.83
Mean 0.88

Hysteretic Curves of Lateral Load Versus Column Displacement

The load-displacement of the investigation of the composite cold formed steel columns are plotted in Figs. 14 to 18
respectively. Illustrate a comparison between the hysteretic loop of composite cold formed columns tests and that calculated from
the finite element program ANSYS. Results shows that finite element has a good agreement with the experimental results of load-
displacement at the top of the column, but at the end of loading, the experimental curve shows some differences, it is noticed that
there are a small differences between finite element and experimental results due to the difference between test setup procedure
and FE model and due to the geometrical imperfection which was not included in the FE model.

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Fig. 14 Comparison between experimental hysteretic loop of column A1 and the calculated from ANSYS

Fig. 15 Comparison between experimental hysteretic loop of column A2 and the calculated from ANSYS

Fig. 16 Comparison between experimental hysteretic loop of column B1 and the calculated from ANSYS

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Fig. 17 Comparison between experimental hysteretic loop of column B2 and the calculated from ANSYS

Fig. 18 Comparison between experimental hysteretic loop of column B3 and the calculated from ANSYS

IV. CONCLUSION C, this indicated that the use of sigma section much
better than ordinary section because of the web and
The behavior of composite cold formed steel columns flange for the sigma section are both stiffened.
under axial and lateral loads has been investigated in this  The specimen with embedded fasteners length of 50 mm
study. Series of laboratory tests has been led to assess the showed more load carrying than specimen with 30 mm
adequacy of the column cross section, fastener spacing and embedded fastener length by 13% due to the embedded
fastener length on column behavior. In view of the test fastener length increases the bond between steel section
information got, the following conclusion are drawn: and concrete.
 The comparison values between ANSYS Workbench and  The highest capacity in carrying the lateral load is found
the experimental lateral cyclic load tests was in great in column A2 consists of 2 sigma cold formed section
understanding. It tends to be inferred that the behavior of covered by 2 plates connected together using 2 fasteners
composite columns can be anticipated from the FEM with length 30 mm in row each side and vertical spacing
programs. of 100 mm.
 The specimen consists of 2 sigma section covered with
plate with 100 mm vertical spacing between fasteners
showed more lateral load capacity than specimen with 2

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