IRJET- Response Analysis of Cold-Formed Dimpled Column

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 06 Issue: 08 | Aug 2019 www.irjet.net p-ISSN: 2395-0072
© 2019, IRJET | Impact Factor value: 7.34 | ISO 9001:2008 Certified Journal | Page 1
Response Analysis of Cold-Formed Dimpled Column
Shilpa Vidyadharan1, Anju Chandran2
1Post Graduate student, Department of Civil Engineering, Sree Buddha College of Engineering,
Elavumthitta, Kerala
2Assistant Professor, Department of Civil Engineering, Sree Buddha College of Engineering, Elavumthitta, Kerala
---------------------------------------------------------------------***----------------------------------------------------------------------
Abstract – Dimpled steel sheets are formed from plain mild
steel sheets by the UltraSTEEL cold-roll forming process
developed by Hadley Industries plc. UltraSTEEL is a cold
rolled forming process that locally work hardens the base
metal. During the forming process, both geometry and
mechanical properties are considerably altered. The strength
of dimpled steel sheets are significantly greater than those of
the original plain steel sheets due to work hardening
developed throughout the forming process. Hence, a number
of advantages can be achieved by altering plain surface steel
column to a dimpled surface steel column.
In this study, the behaviour of plain and dimpled columns of
circular cross-sections has been compared using ANSYS. The
response of the dimpled steel column has been analysed
under lateral impact and axial compressive load. A further
investigation on the energy absorption characteristics of
dimpled column under lateral impact is carried out.
Key Words: UltraSTEEL, Cold-Formed Dimpled Column,
Work Hardening, Specific Energy Absorption, Lateral
Impact.
I. INTRODUCTION
Hollow tubular members are widely used in many
infrastructures. It has been identified in some previous
researches that hollow tubular members are prone to
transverse impact loading. Past research and statistic data
have revealed that accidental collision is one of the main
causes of structural failure. During the collision, the
structural components are exposed to the operating axial
compressive load as well as the lateral impact loads. The
collision energy is absorbed by the tubular members
subjected to bending conditions. In recent years, there is a
particular interest in improving the resistance of tubular
members to lateral impact loads and also improving the
crashworthiness of thin-walled structures from different
angles. Some studies focused on thin-walled columns with
innovative cross-sections. By contrast, some studies
focused on columns made of high strength materials, or
filled by different materials such as concrete, foam or metal
honeycomb core. Although different strategies have been
studied to improve the energy absorption performance of
structural members subjected to lateral impact loads, all
those studies were limited to columns with plain surfaces,
and the effects of introducing concave-convex geometry on
the surfaces have not been previously investigated. The
cold roll forming process is the progressive forming of steel
strip into a desired section by passing through a series of
rolls, arranged in tandem. It is generally the most
economical method of manufacturing sections. The
optimum economic viability in manufacturing industry
requires a minimization of the amount of material used
while the structural performance of roll-formed products
relies on maintaining the stiffness and strength of the
section. Additional bends introduced into the section such
as ‘intermediate stiffeners’ can be a solution for these
conflicting requirements. They have been found to improve
the material properties of the finished product as the yield
and tensile strength of the material increases within the
deformed zone around the bends. However, such
improvements are limited. An alternative mechanism to
improve the material and structural performance is to
impart a deformation to the whole sheet.
2. DIMPLED COLUMNS
Dimpled steel columns are formed from plain mild steel
sheets by the UltraSTEEL® cold-roll forming process
developed by Hadley Industries plc. In this forming process,
plain mild steel coil is progressively fed into a pair of rollers
with rows of specifically shaped teeth and formed into
dimpled steel sheets, as shown in Fig. 1. Dimpled sheets are
then formed into desired profiles by passing through a
series of rolls or press braking. Several previous numerical
and experimental research has revealed that the strengths
of dimpled steel sheets are significantly greater than those
of the original plain steel sheets. The increase in strength is
mainly due to work hardening developed throughout the
forming process. Fig. 2 shows plain column and dimpled
column.
The main objectives of the study are:
 To analyse both plain and dimpled columns of circular
cross-sections under axial compressive load.
 To study the response of dimpled column under both
lateral impact and axial compressive load.

Fig-1: The Ultrasteel® Forming Rollers and Dimpled Steel
Sheet
Fig-2: Plain Column and Dimpled Column
3. METHODOLOGY
 Planning stage
 Validation
 Modelling and Analysis of dimpled column
 Result and Interpretation
4. MODELLING OF STRUCTURE
4.1 Material Properties
The material’s mechanical properties were obtained from
quasistatic tests, following the appropriate British Standard
[2] which is shown in Table 1.
Table-1: Material Properties
Plain
Column
Dimpled
Column
Young's Modulus, E
(GPa)
205 205
Poisson's Ratio 0.3 0.3
Engineering Yield
Strength,
σy,eng (MPa)
278 325
Engineering
Ultimate Strength,
σu,eng (MPa)
368 401
4.2. Dimensional Details
The circular hollow section (CHS) columms are adopted in
this study. The dimensional details of plain column and
dimpled column are shown in Table 2.
Table-2: Dimensional Details
4.3. Modelling
1) Circular Plain and Dimpled Column under Axial Load
The thickness is 1mm for plain column walls and 0.90mm
for dimpled column walls, due to the stretched surface after
the forming process. To obtain the geometric model of the
dimpled plates, the UltraSTEEL® forming process was
firstly simulated using Ansys Workbench, based on a small
square plate with symmetric boundary conditions applied,
as described in [24]. The resultant nodal coordinates were
exported to construct the generic geometric model of
dimpled plates. The geometric models of the dimpled
columns were then created by patterning the generic
dimpled models.
A curved steel strip is placed in a pre-defined position
between the top and bottom rolls to get a curved dimpled
sheet. By symmetry, the curved sheet is transformed fully
to a circular column.
Fig-3: Plain Column
Length of circular column 500mm
Diameter of circular column 37.5mm
Thickness of plain column
wall
1 mm
Thickness of dimpled
column wall
0.90 mm
Size of dimples 2.5mm

Fig-4: Dimpled Column
The external loads were applied in two stages. In the first
stage, a quasistatic constant axial compressive load was
applied on the one end of column while the other end is
fixed. When selecting the axial compressive loads, it was
ensured that the column did neither buckle nor yield solely
under the axial compressive load.
2) Dimpled Column under Combined Axial Compressive and
Lateral Impact Loads
The impact mass was constructed using 8-node solid
elements. The columns were modelled using full-
integration 4-node shell elements with five integration
points throughout the thickness. In the second stage, a
0.1884 kg impact mass with an initial velocity of 4 m/s
along y-axis was applied. The indenter was considered as a
rigid body and translational DOFs of the impact mass were
constrained along x and z directions, in order to represent
the impact mass sliding along a straight trajectory. An axial
compressive load of 6kN is applied at one end of the
column.
Fig-5: Dimpled Column under lateral impact
Fig-6: Boundary Conditions
5. ANALYSIS OF STRUCTURE
5.1 Circular Plain and Dimpled Column under Axial
Load
Static structural analysis is carried out using ANSYS. The
deformed shape of plain column and dimpled column are
shown in Fig. 7 and Fig. 8.
Fig-7: Deformed Shape of Plain Column
Fig-8: Deformed Shape of Dimpled Column

5.2 Dimpled Column under Combined Axial
Compressive and Lateral Impact Loads
The explicit dynamics finite element code integrated in
ANSYS Workbench 16.2 was employed to simulate the plain
and dimpled steel columns’ response to lateral impact
loads. This explicit dynamics FE code is commonly used to
deal with non-linear simulations involving complex contact
interactions.
Fig-9: Deformation in Dimpled Column after lateral impact
Fig-10: Maximum Deformation at the Centre of the Column
In the FE simulations, the automatic node-to-surface
contact function was used to compute the contact between
the indenter and the column, and the trajectory detection
method was used. Symmetric boundary conditions were
applied to the FE model along the axial direction.
6. RESULTS AND DISCUSSIONS
6.1 Circular Plain and Dimpled Column under Axial
Load
The load – deformation curve of plain and dimpled column
under axial compressive load is shown in Fig. 10.
Fig-11: Load Deformation Curve of Plain and Dimpled
Column
Tab-3: Ultimate Load Carrying Capacity
Material
Ultimate Load
(kN)
Deformation
(mm)
Plain Column 116.65 15.791
Dimpled
Column
152.77 23.278
From Table 3, it can be seen that the ultimate load carrying
capacity of dimpled column is 24% greater than that of
plain column. That means they are capable of carrying
greater compressive load than the plain column of same
cross-section. It is clear that the cold work resulting from
the dimpling process produces a significant increase in the
ultimate strength of the dimpled column. During the
dimpling process, work hardening is developed, which has
caused an increase in the equivalent yield strength of the
dimpled column.
6.2 Dimpled Column under Combined Axial
Compressive and Lateral Impact Loads
Fig. 12 shows the impact force vs time graph of dimpled
column under both lateral impact load and axial
compressive load.
0
20
40
60
80
100
120
140
160
180
0 50 100
Load(kN)
Deformation (mm)
Dimpled
column
Plain
column

Fig-12: Impact Force vs Time Graph of Dimpled Column
The maximum impact force obtained for dimpled column
from the graph is 1762.64 kN which is also the second peak
force in the graph. The 1st peak force appears when the
contact between impactor and column starts. The 2nd peak
force which is also the maximum impact force appears
while buckling around the impact location is being
developed.
Fig-13: Energy Absorbed vs Axial Displacement curve of
Dimpled Column
The energy absorbed (EA) – axial displacement curve is
shown in Fig. 12. In this, specific energy absorption (SEA)
was employed as the primary index to evaluate the energy
absorption performance. SEA is calculated based on the
effective crushing distance and it is defined as Eq. (1),
where δ represents the axial displacement, P represents the
impact force, and m represents the mass of the column.
SEA =
∫
= (1)
In Eq. (1), the term ‘EA per unit length of axial displacement’
equals to the gradient of Energy absorbed – axial
displacement curve, while the term ‘Mass of column per
unit length’ is a constant, i.e. 0.1884kg. The linear fitting
method was carried out in order to determine the term ‘EA
per unit length of axial displacement’.
Therefore, on solving the Eq. (1), we get specific energy
absorption (SEA) of dimpled column as 17.17kJ/kg which
shows a better response under low- velocity axial impact
loads.
7. CONCLUSION
From the analysis it is clear that the ultimate load carrying
capacity of dimpled column is 24% greater than that of
plain column. They are capable of carrying greater
compressive load than the plain column of same cross-
section. During the dimpling process, work hardening is
developed, which has caused an increase in the equivalent
yield strength of the dimpled column. From the impact
analysis of dimpled column, the maximum impact force
obtained is 1762.64kN. The specific energy absorption
capacity of dimpled column which is calculated from the
energy absorbed-axial displacement curve is 17.17 kJ/kg,
which is a good result for low- velocity axial impact loads.
ACKNOWLEDGMENTS
The Author(s) wish to express their special gratitude to Dr.
E. V. Nampoothiri, H.O.D, Department of Civil Engineering,
Sree Buddha College of Engineering, Elavumthitta. Above
all, the author(s) thank GOD Almighty for his grace
throughout the work.
REFERENCES
[1] Al-Thairy H, Wang YC (2011), “A numerical study of the
behaviour and failure modes of axially compressed steel
columns subjected to transverse impact”, Int J Impact
Eng;38:732–44
[2] British Standard, BS EN 10002-1:2001. Metallic
Materials – Tensile Testing – Part 1: Method of Test at
Ambient Temperature, 2001.
[3] Ce Lianga, Chang Jiang Wanga (2018), “Behaviour of
cold-formed dimpled columns under lateral impact”, Eng
Struct. 163 167–176
[4] Hartley P, Pillinger I (2001), “Developments in
computational modelling techniques for industrial metal
forming process”, Proc Inst Mech Eng B: J Eng
Manuf;215:903–14
[5] H. Huh, W.J. Kang (2002), “Crash-worthiness assessment
of thin-walled structures with the high-strength steel
sheet”, Int. J. Veh. Des. 30 (1/2) 1–21
[6] Lecce M, Rasmussen KJR (2006), “Distortional buckling
of cold-formed stainless steelsections: experimental
investigation”, J Struct Eng;132:497–504
[7] Liang C, Wang CJ (2017), “Experimental and numerical
study on crashworthiness of cold-formed dimpled steel
columns”, Thin-Walled Struct;112:83–91
[8] Nguyen VB, Wang CJ (2014), “Dimpling process in cold
roll metal forming by finite element modelling and
experimental validation” J Manuf Process;16:363–72
-500
0
500
1000
1500
2000
0 0.0001 0.0002 0.0003
ImpactForce(kN)
Time (s)
Impac
t
Force
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
0.00E+00 2.00E-01 4.00E-01 6.00E-01
EnergyAbsorbed(kJ)
Axial Displacement (mm)
Energy
Absor…

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