Essay: Cold-formed steel columns

Chapter 1:
INTRODUCTION
Steel can be classified in to two main groups that is hot-rolled shaped and cold-formed steel sheet. The usage of cold-formed steel channel in building construction began in1980’s, where United State and Great Britain are the first country that is using this technology. It can be used as individual structure framing member in shape of channel section, zee-section, I-section and many others. This type of individual member is to carry load, structural strength and stiffness are the main considerations in design. Such sections can be used as primary framing members in building up to six stories height.
Generally cold-formed steel sections have several advantages if compared to other construction materials. The main advantages are no insect and fungal infection, as to compared with hot-formed steel channel, cold-formed are much lighter thus reducing the weight of the structure, speedy in construction and suit for site erection because worker at site could easily maneuver the member such as cut, bend and others if there is any problem at site, consistency and accuracy of profile because it is fabricated in a control manufacturing process. Moreover, most of the process is controlled by machine and computer, and more economic and easy for transport handling to site or confined space.
Due to the advantages, the application of the cold-formed steel has been widely used as structural and non-structural materials. Some of the applications are as trusses for roofing, floor deck, portal frame, wall framing, cladding support member and others.
An element which is supported by webs along both its longitudinal edges is called a stiffened element. There are two types of stiffener that is ‘edge stiffener’ which is located at the edge of the element and the other one is called ‘intermediate stiffener’ which is located internally within a plate. The edge stiffener must possess sufficient rigidity or it may buckle perpendicularly to the plane of the element to be stiffened. Intermediate stiffeners are widely used in cold steel member. As with edge stiffeners, the intermediate stiffeners must have adequate rigidity to prevent deflection in the element in the region of the stiffener.
Local buckling occurs where the axis of the member is not distorted, but the strength of the cross section is compromised by the buckling component of the cross section. It is an extremely important factor of cold-formed steel sections on account of the fact that the very thin elements used invariably buckle before yielding. The thinner the plate, the lower will be the load at which buckles will form. The distortional buckling involves both rotational and translational at the corners of the translation. It occurs when the cross section is weak in torsion and these are usually applies to open sections which the thickness is thin. Thin-walled flexural or compression members composed of high strength steel, which are braced against lateral or flexural torsional buckling, may undergo a mode of buckling commonly called distortional buckling.
One of the biggest difficulties with cold-formed steel design is the prevention of member buckling. Because of the low thickness to width ratio, it is likely that the members will buckle at stresses that are lower than the yield stress when compressive, bearing, and shear bending forces are applied. Therefore, buckling is a major design consideration for all cold-formed steel, which is unlike the behavior of hot-rolled steel where steel yielding is the leading design consideration.
Chapter 2:
LITERATURE REVIEW
1) Narayanan, S. and Mahendran, Mahen (2003) :’Ultimate Capacity of Innovative Cold-formed Steel Columns’. This paper describes the distortional buckling behaviour of a series of innovative cold formed steel columns. More than 15 laboratory experiments were undertaken first on these innovative steel columns of intermediate length under axial compression. All of these columns failed by distortional buckling with very little post-buckling strength. The section and buckling properties of the columns were determined using the finite strip analysis program THINWALL. The distortional buckling and nonlinear ultimate strength behaviour of the columns was investigated in detail using finite element analyses (ABAQUS). The finite element analyses included relevant geometric imperfections and residual stresses. The deflection and strain results from the experiments compared well with those from the analyses. The ultimate design load capacities were evaluated using the provisions of Australian Cold-formed Steel Structures Standard AS/NZS 4600-1996, and were compared with those from experiments and finite element analyses. A series of parametric studies was also carried out by varying the yield strength, thickness and column length. Details of this investigation and the results are presented in this paper.
2) M. Macdonald, M.A. Heiyantuduwa, J. Rhodes (2008): ‘Recent developments in the design of cold-formed steel members and structures’. In this paper the main types of cold-formed steel members are described, the particular characteristics affecting their design are discussed, as are the ways in which design specifications deal with these characteristics. The various types of buckling which can occur, and which may interact with each other to promote failure at loads substantially less than those, which would be obtained in the absence of these effects. The complications induced by such effects must be taken into account in design, if the potential benefits offered by the use of such members are to be realised, and in recent design specifications this has been realised.
3) Pedro B. Dinis, Dinar Camotim (2010): ‘Post-buckling behaviour and strength of cold-formed steel lipped channel columns experiencing distortional/global interaction’. This paper reports the results of a numerical investigation concerning the elastic and elastic’plastic post-buckling behaviour of cold-formed steel lipped channel columns affected by distortional/global (flexural’torsional) buckling mode interaction. The results presented and discussed were obtained by means of analyses performed using the finite element code ABAQUS and adopting column discretisations into fine4-node iso-parametric shell element meshes. The columns analysed (i) are simply supported (locally/globally pinned end sections that may warp freely), (ii) have cross-section dimensions and lengths that ensure equal distortional and global (flexural’torsional) critical buckling loads, thus maximising the distortional/global mode interaction effects, and (iii) contain critical-mode initial geometrical imperfections exhibiting different configurations, all corresponding to linear combinations of the two ”competing” critical buckling modes.
4) Jia-Hui Zhang, Ben Young (2011): ‘Compression tests of cold-formed steel I-shaped open sections with edge and web stiffeners’. In this research, a series of column tests on cold-formed steel I-shaped open sections with edge and web stiffeners were conducted. The column specimens were compressed between fixed ends. The columns were failed by local, distortional, flexural buckling and the interaction of these buckling modes. The failure modes and ultimate strengths of the column specimens were presented. The direct strength method in the North American Specification and the Australian/New Zealand Standard was used to calculate the design strengths of the I-shaped open section columns. The appropriateness of the direct strength method for I-shaped open sections with edge and web stiffeners was evaluated. In addition, the reliability of the direct strength method for the I-shaped open sections was evaluated using reliability analysis. It is shown that the direct strength method can be used for cold-formed steel I-shaped open sections with edge and web stiffeners.
5) Thomas H.-K. Kang, Kenneth A. Biggs, and Chris Ramseyer (2013): ‘Buckling Modes of Cold-Formed Steel Columns’. This paper aimed at studying different buckling modes, determine the buckling mode and maximum buckling capacity of the built-up C-channels, and evaluate as per the AISI-2001 Specification. For these goals, the following was conducted: 1) different buckling modes of cold-formed steel columns were investigated; 2) previous research on built-up columns and testing rigs for column buckling was reviewed; and 3) the authors’ buckling test results of 42 cold-formed built-up columns were examined.
6) G.Vani, P.Jayabalan, Jikhil Joseph (2013): ‘Numerical Analysis of Cold Formed Steel Plain Angle Compression Members’. In this paper ultimate load carrying capacity of the angle compression members subjected to pin end conditions are obtained using numerical and analytical methods. Three nominal section sizes were tested, ranging from non-slender to slender sections. The specimens were studied for b/t ratio such as 30, 45 and 60. The width was varied and the thickness (2 mm) was kept constant. They were analyzed for different lengths such as 300mm, 600mm, 900mm and 1200 mm. Detailed measurements of material properties were done by the tensile coupon test. The specimens were subjected to pressure loading to study the behavior of various sections. From the finite element analysis it was observed that the load carrying capacity of the section decreases as the b/t ratio increases. For the same b/t ratio as the length increases the load carrying capacity of the section decreases due to the slenderness effect. The non-linear analysis results were compared with the recent Direct Strength Method (DSM) and the traditional Effective Width Method (EWM) as well. The DSM method is found to predict the ultimate load capacities in a better way.
7) Sreedhar Kalavagunta1, Sivakumar Naganathan and Kamal Nasharuddin Bin Mustapha (2013) : ‘ Experimental Study of Axially Compressed Cold Formed Steel Channel Columns’, In this paper Axial compression tests on cold-formed lipped channel sec��tions were conducted. A total of 27 lipped channel specimens were tested. This paper has outlined two current approaches to the design of lipped channel sections using an extension to the DSM in AISI and EWM in BS5950-5 specifications as well as the test results. The DSM employs gross cross sec��tional area were as EWM follows effective plate width for calculating cross section capacity. The experimental test results are very close to DSM and EWM methods.
8) S.A.Kakade1, B.A.Bhandarkar, S.K. Sonar, A.D.Samare (2014): ‘Study of various design methods for cold ‘ formed light gauge steel sections for compresive strength’. This paper provides an experimental investigation for the compressive strength of Cold ‘ Formed light gauge steel plain (stiffened) tubular sections. The test specimens were brake pressed from high strength structural steel sheets. In addition, the test strengths were compared with the design strengths calculated using the Indian Standard and North American Specification for Cold ‘Formed steel structures. Compression members are linear members in which axial forces act to cause elongation (stretch). Such members can sustain loads up to the ultimate load, at which stage they may fail by rupture at a critical section. However, if the gross area of the member yields over a major portion of its length before the rupture load is reached, the member may become non ‘ functional due to excessive elongation. I.S. 801- 1975 is in Working Stress Method (W.S.M.) and in (M.K.S.) system. So it is required to study Allowable Stress Design (A.S.D.), Load and Resistance-Factor-Design (L.R.F.D.) and Limit State Method (L.S.M.).It is revealed that the design strengths predicted by the Specification and Standard are generally very conservative. It is observed that some specimen show lower strength than the value predicted by the American Iron and Steel Institute.
9) P. B. Patil, P. D. Kumbhar (2015): ‘Parametric study of light gauge steel lipped channel column section’. In this paper the experimental study of structural behavior of light gauge steel lipped channel sections under eccentric loading by varying loading position in between center of gravity and shear center of channel column section is done. Finite element analysis of the section is also done using ABAQUS software for different positions of the load. The results indicate that, load carrying capacity of the section increases as the loading position shifts towards supported edge of the section. The failure of the section occurs in the form of local-distortional buckling approximately between 1/3rd – �� of the height of column. Results obtained by software were close to experimental results.
Chapter 3:
OBJECTIVES
The following are the main objectives of this project:
1) To study various modes of buckling occurring in cold formed steel members when subjected to axial loading.
2) To calculate the Load Carrying Capacity of a Cold formed steel columns of Plain Channel Section, Lipped channel section and Lipped channel with intermediate stiffener using IS 801-1975, British Standard (BS) 5950-5:1998 and by ABAQUS software.
3) To conduct experimental tests on Cold formed Steel column of Plain Channel Section, Lipped channel section and Lipped channel with intermediate stiffener.
4) To compare the Load Carrying capacity of a Cold formed steel Column analysed as per IS 801-1975, BS 5950-5:1998, software based results obtained from ABAQUS and experimental test results.
Chapter 4:
GEOMETRY OF COLD FORMED STEEL COLUMNS
4.1 Geometry:
A total nine (9) models of three different types of cross section shapes with the length varies of 500 mm, 650 mm, 900 mm were adopted in this study. The cross section shape namely Plain-channel section (P), Lipped-channel section (L) and Lipped channel with intermediate stiffener (S) were selected to perform analysis by using ABAQUS as shown in Figure 1.
(a) (b) (c)
Figure 1: Different Cross Section of Finite Element Models:
(a) Plain-channel section (P),
(b) Lipped-channel section (L),
(c) Lipped-channel with intermediate stiffener (S)
All the models have same geometrical properties such as 80mm in breadth (b), 200mm in depth (d) and 2mm in thickness (t). Besides that the details of models including the lipped size and the intermediate stiffener size are presented in Table 1.
The columns are labeled such that the channel section shape, size of edge stiffener and the column length could be identified from the label. For instance, the label ‘L-500’ defines a column having a lipped channel section, indicated by the letter ‘L’ followed by the length of column in mm i.e.500mm length.
The measured cross-section dimensions and the material properties such as Modulus of Elasticity and Poisson’s ratio were included in the finite element model. All the channel sections were modeled by thin shell element in ABAQUS. Both ends were tied with MPC constraint and the load was given at the CG of the section.
4.2 Supports
Both ends are taken as fixed support. The loading is applied at the CG of the section.
Table 1: Dimension of model
Specimen Modeling L
mm d
mm b
mm t
mm D
mm ds
mm bs
mm
P-500 500 140 60 2 0 0 0
P-650 650 140 60 2 0 0 0
P-900 900 140 60 2 0 0 0
L-500 500 140 60 2 20 0 0
L-650 650 140 60 2 20 0 0
L-900 900 140 60 2 20 0 0
S-500 500 140 60 2 20 20 10
S-650 650 140 60 2 20 20 10
S-900 900 140 60 2 20 20 10
Chapter 5:
REFERENCES
1) G.Vani, P.Jayabalan, Jikhil Joseph, ‘Numerical Analysis of Cold Formed Steel Plain Angle Compression Members’, International Journal of Emerging Technology and Advanced Engineering, Volume 3, Issue 4, Page No:22-29, October 2013
2) Jia-Hui Zhang, Ben Young, ‘Compression tests of cold-formed steel I-shaped open sections with edge and web stiffeners’. Thin Walled Structures73 (2013).
3) M. Macdonald a,, M.A. Heiyantuduwa, J. Rhodes, ‘Recent developments in the design of cold-formed steel members and structures’, Thin-Walled Structures 46 (2008) 1047′ 1053.
4) Pedro B. Dinis, Dinar Camotim, ‘Post-buckling behaviour and strength of cold-formed steel lipped channel columns experiencing distortional/global interaction’, Computers and Structures 89 (2011), Page No: 422-434.
5) P. B. Patil, P. D. Kumbhar, ‘Parametric Study of Light Gauge Steel Lipped Channel Column Section’, International Journal of Research in Engineering and Technoogy, Volume 4, Issue 06, Page No: 79-84, June 2015.
6) Shanmuganathan Gunalan, Mahen Mahendran, ‘Improved design rules for fixed ended cold-formed steel columns subject to flexural’torsional buckling’, Thin Walled Structures73 (2013) Page No: 1’17.
7) Sreedhar Kalavagunta, Sivakumar Naganaathan, Nasharuddin Bin Mustapha, ‘Experimental Study of Axially Compressed Cold Formed Steel Channel Columns’, Indian Journal of Science and Technology, Vol 6(4), Page No: 4249-4254, April 2013.
8) S. Narayanan and M. Mahendran, ‘Ultimate Capacity of Innovative Cold-formed Steel Columns’, Journal of Constructional Steel Research 59(4):pp. 489-508.
9) S.A.Kakade, B.A .Bhandarkar, S.K. Sonar, A. D. Samare, ‘Study of various design methods for cold ‘ formed light gauge steel sections for compresive strength’, International Journal of Research in Engineering and Technology, Volume 3, Page No 10-13.
10) Thomas H.-K. Kang, Kenneth A. Biggs, and Chris Ramseyer, ‘Buckling Modes of Cold-Formed Steel Columns’, IACSIT International Journal of Engineering and Technology, Vol. 5, No. 4, August 2013.