International Conference on Engineering Innovations and Solutions(ICEIS – 2016)
EXPERIMENTAL STUDY ON THE TORSIONAL
BEHAVIOUR OF COLD−FORMED STEEL
CHANNEL SECTION CONNECTED BACK TO
BACK.
Ajeet Sharma
Dr.S.Senthil Selvan
P.G. Student, Department of Civil Engineering, SRM University
Chennai, India,
Absrtrct:-The CFS structural systems are characterized by high
productivity, especially when innovative connection technology
as press-joining, clinching are used. The cold-formed steel
sections are manufactured from steel sheets. Built up I section
formed by using symmetric channel section connected back to
back with the help of bolts provided in the web part of section.
For the experimental study, two specimen of dimension of a
230mm × 100mm × 3mm with a lip of 30mm and two
specimens of dimension of 180mm x 50mmx1.6mm with a lip
of 20 mm and 1.8 m length were tested under the self straining
loading frame of capacity 40 tons. The IS: 801-1975 code is
based on working stress method and BS 5950-5:1978 code is
based on limit state method. It was observed that both the
design concepts give nearly the same strength, moment and
angle of twist were also similar to some extent.
Keywords:- Cold−formed steel, lipped channel section, Back to
back connection, torsoinal behaviour.
I. INTRODUCTION
The CFS structural systems are characterized by high
productivity, especially when innovative connection
technology as press-joining, clinching are used. The coldformed steel sections are manufactured from steel sheets. By
cutting and bending into desired shapes. In the same way,
the specimen chosen here is a channel lipped section
connected back to back with bolts. The cold-formed sheet is
also known as Light gauge steel because of its minimum
thickness when compared to hot rolled section In Steel
structures, two primary structural steel member types are
used: hot-rolled steel members and cold-formed steel
members. Hot-rolled steel members are formed at elevated
temperatures, whereas cold-formed steel members are
formed at room temperatures. Until recently, the hot-rolled
steel members have been recognized as the most popular
and are widely used steel group, but since then the use of
E-ISSN :2348 – 8352
Professor, Department of Civil Engineering, SRM
University, Chennai, India,
cold-formed high strength steel structural members has
rapidly increased.
In general, cold-formed steel beams have open
where the centroid and shear centre do no coincide. When a
transverse loaded is applies away from the shear centre it
causes torque. Because of open nature of the section, it is
subjected to torsional induces warping in the beam. The
thickness typically ranges from 1.2mm to 3.5mm The
typically design strength for cold formed steel section are
350N/mm2 450 N/mm2 550 N/mm2 .Cold formed steel
sections are generally applied in the construction on both
primary and secondary structural members. The variety of
size and thickness of CFS profiles provides high flexibility
in design.
The paper, presents the experimental and
theoretical studies on the torsional behaviour of cold-formed
steel beams. The purpose of this paper is to present a series
of torsional tests on CFS lipped and without channel section
beams under restrained boundary conditions. In the previous
researches, flexural tests of thin-walled section with and
without lip channel sections with warping and torsional
restraints have not been performed. Therefore, the test
strengths of such sections are not known. This paper
provides the test strengths of channel with and without lip
beams. The various specimen details are shown in table 1
The selection of the section based on the basis of different
physical properties of cold-formed steel section as shown in
table 2 of the section. The magnitude of the warping stresses
can be as high as the bending stresses in some cases. If the
beam is not continuously restrained against torsion and
lateral movement, it may fail in non-uniform torsion, that is,
torsion combined with warping. Present design practice is
based on lateral-torsional buckling or on linear bending and
warping stress distributions, either of which is not
completely realistic.
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Table No: 1 Specimens detail
The required minimum depth of the lip should be
Specimen(mm)
Dimension(mm)
Length(mm)
S-1
230x100x2
1800
S-2
S-3
230x100x25x2
180x50x1.6
1800
1800
S-4
180x50x20x1.6
1800
lim −
dmin = 2.8t
Theoretical Investigations of Built-Up Channel Section by
the code of Practice, Load Carrying Capacity given below
for the different section:-
Table 2 Properties of the Light Gauge Section
300
7850 kg/mm3
Modulus Of Elasticity
5
2
2 × 10 N/mm
Poisson’s Ratio
0.3
Modulus of Rigidity
76900 N/mm2
Load (kN)
Density
> 4.8t
250
IS 801:1975
200
BS 5950
150
100
50
0
II. THEORETICAL INVESTIGATION
Computation of effective width
The effective width of compression flange will be found on
the basis of design stress
fb = 0.6 fy
where fy = 235 N/mm2 fb = 0.6 × 235 = 141 N/mm2
[ 1-
35
30
25
20
15
10
5
0
IS 801:1975
BS 5950
S-1
S-2
S-3
S-4
Specimens (mm)
Specimen (mm)
=
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S4
Table:- 3 Theoretical value of angle of twist.
]
Where, w – flat width of the compression element, t –
thickness of the element, b – effective width of the element,
f – Basic design stress
( )lim
S3
Theoretical Investigations of Built Up Channel Section by
the Code of Practice, Moment of Resistance given below:-
For load determination, effective width is given by the
equation,
=[
S2
Specimens(mm)
M0ment of Resistance(kN-m)
The present study is carried out to understand the torsional
behaviour of cold formed light gauge steel using IS: 8011975 & BS 5950-5:1998. Different countries use different
codes as per Indian standard IS: 801-1975 is a code of
practice for use of cold-formed light gauge steel structural
members in general building construction the design of
members is carried out by working stress method whereas
the BS: 5950-5:1998 structural use of steelwork in building
– Part5. Code practice for design of cold formed thin gauge
sections, here the design of members is carried by limit state
method. Thus, results for both IS code & BS codes obtained
are then compared.
S1
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S-1
Theoretical angle of
twist (radian)
34.95
S-2
S-3
38.44
15.47
S-4
14.90
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International Conference on Engineering Innovations and Solutions(ICEIS – 2016)
III. EXPERIMENTAL STUDY
Lateral torsional buckling is a limit state of structural
usefulness where the deformation of a beam changes from
predominantly in-plane deflection to a combination of
lateral deflection and twisting while the load capacity
remains first constant, before dropping off due to large
deflections.
The various factors affecting the lateral-torsional buckling
strength are:




Distance between lateral supports to the
compression flange.
Restraints at the ends and at intermediate support
locations.
Type and position of load Moment gradient along
the length.
Type of cross-section. Material properties, Initial
imperfections of geometry and loading
After fabrication of specimen with 230mm and 180mm
depth as shown in fig(1), fig(2), fig(3) and fig(4). The strain
gauges are placed in the mid portion where the deflection
attains due to the twisting of the section. After placing the
strain gauges, the steel beam should be placed in the loading
frame. Then the loading beam which is having two steel rod
at the desired distance for applying load to the angle section
was placed over the angle section in loading frame Then the
hydraulic jack and proving rings are placed over the loading
beam. Then load was applied through hydraulic jack and
applied load was determined by the proving ring. The strain
gauges are used to note the result. The load is applied till the
section attains ultimate load capacity and buckles. The
arrangement of the specimen with and without lip in the
loading frame is shown in Fig (5), Fig (6). The strain gauges
are provided at the web part of the beam with is connected
to the strain indicator in order to take the strain value.
Fig:- 1 Built-up I section (S-1)
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Fig:- 2 Built-up I section(S-2)
Fig:-3 Built-up I section(S-3)
Fig:- 4 Built-up I section(S-5)
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International Conference on Engineering Innovations and Solutions(ICEIS – 2016)
IV. RESULT AND DISCUSSION
. The experimental results were found to be precise as
compared to theoretical values. The comparison of angle of
twist obtained from theoretical investigation
and
experimental investigation is shown in table 4
Table:- 4 Comparison of angle of twist values.
Specimen (mm)
Fig:-5 Test set up of beam for torsional.
Experimental
angle of twist
(radian)
S-1
Theoretical
angle of
twist
(radian)
34.95
S-2
S-3
38.44
15.47
25.66
14.15
S-4
14.90
12.032
23.49
V.CONCLUSION

A comparative study on the torsional strength of
lipped and without lipped channel sections based
on different code provisions.

With the increment of depth the strength and
stiffness of the beam also increases.

All the beam failed at local buckling of the top
flange. This mode of failure is mostly seen in coldformed steel as compared to hot rolled steel.

The determined ultimate load value is compared to
the numerical values. This values are helps to use
the light gauge angle sections as secondary beams.

The angle of twist obtained from theoretical
investigation is 32.79% and 33.24% more than that
of experimental values for specimen S-1 and S-2.

The angle of twist obtained from theoretical
investigation is 8.53% and 19.24% more than that
of experimental values for specimen S-2 and S-4.

The back to back cold formed steel angle section
properties are studied. The fabrication process of
the back to back steel angle section was studied.

The section was fully buckled and strain gauge,
proving ring values are noted down. Then the
values are used to plot graph such as load versus
strain.
Fig :-6 Twisting of beam.
The variation of strain with the increment of load for
specimen of all classes are shown in fig 5.
60
Strain (µ)
50
40
S-1
30
S-2
20
S-3
10
S-4
0
0 4 8 12 16 20 24 28 32 36 40 44
Load(kN)
Fig:-7 Load vs Strain curve of steel beams for Torsion.
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International Conference on Engineering Innovations and Solutions(ICEIS – 2016)
Acknowledgement
I would like to add a few heartfelt words for the
people who have been part of this dissertation by
supporting and encouraging me. At the onset, I
would like to thank ALMIGHTY. I would also like
to express my Deepest Gratitude to my guide Prof
S.Senthil Selvan, Civil Department, SRM
University, Chennai, Tamil Nadu India for
supporting me during project work and guiding me
with his valuable suggestions. I attribute all my
success in life to My Parents for their moral and
intellectual support. It is my greatest pleasure to
dedicate this achievement to My Parents.
References
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E-ISSN :2348 – 8352
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