comp test on c section

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INTERNATIONAL JOURNAL OF APPLIED ENGINEERING RESEARCH, DINDIGULVolume 1, No1, 2010

Copyright 2010 All rights reserved Integrated Publishing Association

RESEARCH ARTICLE ISSN - 0976-4259

28

Investigation on Cold - formed C - section Long Column with IntermediateStiffener & Corner Lips Under Axial Compression

M. Meiyalagan 1 M.Anbarasu 2 and Dr.S.Sukumar 3

1 P.G.Student, Department of Civil Engineering, Government College of Engineering,Tamil Nadu, India.

2 Research Scholar, Department of Civil Engineering, Government College of Engineering,Tamil Nadu, India

3 Assistant Professor and Head, Department of Civil Engineering, Government College of Engineering, Tamil Nadu, India

[email protected]

Abstract

The Present thesis work aims at the study of buckling behavior of open webOpen cross section with intermediate stiffener & corner Lips under compression. Introductiondeals with the general idea about cold formed steel members, problems on investigationneed for this Thesis, objective of the investigation, scope of the thesis methodology.Literature review details the review of the literature on torsional flexural buckling,Distortional buckling, Channel section with Stiffened Lip and Cold formed members andOpen web sections. Expressions for distortional buckling stress & flexural torsional bucklingstress has been obtained for mono symmetric open cross section compression members. Four test specimens have been fabricated with geometry of C- Section with stiffened bothWeb and Flange with various thickness and experimented. Numerical analysis using FEMSoftware ANSYS 11 is performed on the tested models and the results are comparedwith the Experimental results. Design for maximum Limit strength of Columns using IndianStandard (IS 801 - 1975) is to be calculated.

Comparison of experimental and analytical results using ANSYS and IndianStandard method values are presented under results and discussion. Finally Conclusionand scope for future work is presented based on the results.

1.Introduction

Cold-formed steel products are found in all aspects of modern life; in thehome, the shop, the factory, the office, the car, the petrol station, the restaurant, and indeedin almost any imaginable location. The uses of these products are many and varied,ranging from tin cans to structural piling, from keyboard switches to mainframe

building members. Nowadays, a multiplicity of widely different products, with atremendous diversity of shapes, sizes, and applications are produces in steel using thecold forming process.

Cold-formed steel products such as sections have been commonly used in themetal building construction industry for more than 40 years. The popularity of these

products has dramatically increased in recent years due to their wide range of application,economy, and ease of fabrication, and high strength-to weight ratios. In market variousshapes of these products are available C-sections are predominantly used in light load and
mailto:[email protected]


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medium span situations such as roof systems. Their manufacturing process involves formingsteel sections in a cold state (i.e. without application of heat) from steel sheets of uniformthickness.

The use of cold-formed steel structures is increasing throughout the world with the production of more economic steel coils particularly in coated form with zinc or aluminum /zinc coatings. These coils are subsequently formed into thin-walled sections by thecold-forming process. They are commonly called Light gauge sections since their thickness has been normally less than 2.0 mm. However, more recent developments haveallowed sections up to 25 mm to be cold-formed, and open sections up to approximately 8mmthick are becoming common in building construction. The steel used for these sections mayhave a yield stress ranging from 250 MPa to 550 MPa. The higher yield stress steels arealso becoming more common as steel manufacturers produce high strength steel moreefficiently.

Further, the shapes which can be cold-formed are often considerably more complexthan hot-rolled steel shapes such as I-sections and unlipped channel sections. The cold-formed sections commonly have mono- symmetric or point symmetric shapes, andnormally have stiffening lips on flanges and intermediate stiffeners in wide flanges and webs.Both simple and complex shapes can be formed for structural and non-structural applicationsas shown in Figure. Special design standards have been developed for these sections.

The market share of cold-formed structural steelwork continues to increase in thedeveloped world. The reasons for this include the improving technology of manufacture andcorrosion protection which leads, in turn, to the increase competitiveness of resulting

products as well as new applications. Recent studies have shown that the coating loss for galvanized steel members is sufficiently slow, and indeed slows down to effectively zero,than a design life in excess of 60 years can be guaranteed.

The range of use of cold-formed steel sections specifically as load-bearing structuralcomponents is very wide, taking in the Automobile industry, Shipbuilding, Rail transport, the

Typical Cold Formed Steel


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Aircraft industry, Highway engineering, Agricultural and Industry equipment, Officeequipment, Chemical, Mining, Petroleum, Nuclear and Space industries.

1.1 Application Cold forming has the effect of increasing the yield strength of steel, the increase being

the consequence of cold working well into the strain-hardening range. These increases are predominant in zones where the metal is bent by folding. The effect of cold working is thusto enhance the mean yield stress by 15% - 30%. For purposes of design, the yield stress may

be regarded as having been enhanced by a minimum of 15%.In general, cold-formed light gauge steel structural members provide the following

advantages in building construction:v Cross sectional shapes are formed to close tolerances and these can be

consistently repeated for as long as required.v Cold rolling can be employed to produce almost any desired shape to any

desired length.v Pre-galvanized or pre-coated metals can be formed, so that high resistance tocorrosion, besides an attractive surface finish, can be achieved.

v All conventional jointing methods, (i.e. riveting, bolting, welding andadhesives) can be employed.

v High strength to weight ratio is achieved in cold-rolled products.v They are usually light making it easy to transport and erectv As compared with thicker hot rolled shapes, more economical design can be

achieved for relatively light loads and/or short spans.v Unusual sectional configuration can be economically produced by cold-

forming operation, and consequently favorable strength-to-weight ratios can be obtained.

v Load carrying panels and decks can provide useful surfaces for floor, roof, andwall constructions, and in other cases they can provide enclosed cells for electrical and other conduits.

v Load carrying panels and decks not only withstand loads normal to their surfaces, but they can also act as shear diaphragms to resist force in their own

planes if they are adequately inter connected to each other and to supportingmembers.

1.2 Characteristics Of Cold Formed Steel Structural Members

v Compared with other materials such as timber and concrete, the followingqualities can be realized for cold-formed steel structures members.

vLightnessv High strength and stiffness

v Ease of prefabrication and mass productionv Fast and easy erection and installation.v Substantial elimination of delays due to weather.v More accurate detailing.v Non- shrinking and non- creeping at ambient temperature.v Form work unneeded.v Termite proof and rot- proof.


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v Uniform quality.v Combination of the above mentioned advantages result in cost saving during

constructions.

1.3 Behaviour Under Axial compression

Non Symmetric open web cross sections (whose centroid does not coincide with shear centre) will undergo flexural torsional buckling. Single symmetric sections will likely tofail flexural buckling, or flexural torsional buckling depending on their actual sizes. Doublesymmetrical members, may be susceptible to lateral torsional buckling (flexural buckling)due to the presence of the imperfections. Pure torsional buckling modes are likely to occur for

point symmetric sections in which the shear centre and centroid coincides. Lateral torsional buckling (or flexural torsional buckling) FT is a combination of flexural buckling (F) andtorsional buckling (T). Long columns fail in flexural or flexural torsional buckling andshort columns in distorsional buckling.

1.4 Types of Buckling

i) Local Bucklingii) Distorsional Bucklingiii) Eulers buckling (Flexural or flexural torsional)

1.5 Local Buckling:

The plate elements of Cold formed sections are normally thin higher plateslenderness ratio and hence they buckle locally before yield stress is reached, Local bucklingmode of a given thin walled member depends, on its i) cross section geometry (shape &dimensions) and ii) and support conditions. The elastic local buckling of thin elements doesnot immediately lead to failure. The elements can carry additional load in the post bucklingstrength before failure occurs. The Post buckling strength of elements having relativelylarge flat width to thickness ratio may be several times the load that causes local buckling.Consequently all the cold formed design specifications take into account the post

buckling strength.

1.6 Flexural Buckling:

In this mode compression buckles out weaker principle axis & collapses occur at rate

following excessive buckling deformation (no twisting). Normally, Long columns willundergo flexural buckling along half wave lengths.

1.7 Torsional Buckling:

In the Torsional buckling mode, the members fails by twisting about the longitudinalaxis through the Shear centre (No bending).

1.8 Flexural - Torsional Buckling:


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Due to the smaller thickness the section have low torsional stiffness and their shear centre and centroid are located away from each other. This causes flexural torsional

buckling (simultaneous bending and twisting).

1.9 Distorsional Buckling:

Distorsional buckling, also known as Stiffener buckling or Local torsional buckling is mode characterised by a rotation of the flange at the flange Web junction innumbers with edge stiffened elements. In members with intermediate stiffened elementsdistorsional buckling is characterized by displacement of the intermediate stiffener normal tothe plane of the element.

2. Experimental Study:

To get insight of the behaviour and the mode of failure of C- section Column of OpenCross section with Web Stiffened Under Compression.

Properties of Specimen:

One Specimen in each thickness is tested to determine the modulus of elasticity andyield stress for steel.

Tension Test on Steel Sheet:

IS 1608 2005 (Part I) prescribes the method of conducting tensile test on steelsheet strip less than 3mm and not less than 0.5mm thick.

Test Specimen:

v The test piece has a width b of 20mm and gauge length lo of 80mm.However, if the nominal thickness a is not greater than 2mm, the test piecemay have a width of 12.5mm and a gauge length lo of 50mm.

v The test piece generally has enlarged ends in which case there is a transitionradius of not less than 20mm between the griped ends and the parallel lengths.The Width of the enlarged ends is not less than 20mm and not more than40mm. alternatively; the test piece may consist of a strip with parallel sides.

vThe ends of the test piece metal held in suitable grips in the testing machine insuch a way that the centre line of pull coincides with the longitudinal axis of the test piece.


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v The parallel length is kept between Lo + b/2 & Lo + 2b.

Tension test on Steel Sheet

Where,Lo = Original Gauge lengthLe = Parallel lengthLt = Total length

b = Width of the test piece

2.1 Rate of Loading

If the Yield stress is to be determined, the speed of the machine should be soregulated that the rate of increase of stress on the test piece is not more than 1Kg/Sq.mm/Sec.from a stress vs. approximately 5Kg/Sq.mm until the yield point is reached. The Graphs were

plotted and the Youngs modulus and the Yield stress were calculated.

Load in KN Deflection in mmStress inN/ mm2 Strain

0 0 0 00.9 0.009 0.035714286 0.00011.8 0.023 0.071428571 0.0002562.7 0.0276 0.107142857 0.0003073.6 0.0437 0.142857143 0.0004865.4 0.06325 0.214285714 0.000703

6.3 0.069 0.25 0.0007677.2 0.07245 0.285714286 0.0008058.1 0.08855 0.321428571 0.000984

9.3885 0.09545 0.372559524 0.0010619.7455 0.2944 0.38672619 0.003271

10.8 0.3887 0.428571429 0.00431910.8157 0.4025 0.429194444 0.00447210.155 0.7935 0.40297619 0.008817


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11.43 1.0005 0.453571429 0.01111711.745 1.2075 0.466071429 0.01341712.165 1.8124 0.482738095 0.020138

12.73125 2.093 0.505208333 0.02325612.8625 2.4025 0.510416667 0.026694

13.25625 2.9877 0.526041667 0.03319713.335 3.3005 0.529166667 0.03667213.335 3.7007 0.529166667 0.04111911.85 3.77775 0.470238095 0.04197511.27 4.002 0.447222222 0.04446710.8 4.0825 0.428571429 0.045361

10.26 4.2205 0.407142857 0.0468949 4.4137 0.357142857 0.049041

7.4835 4.7173 0.296964286 0.0524146.9 4.8185 0.273809524 0.053539

6.513 4.98295 0.258452381 0.055366

0

0. 1

0. 2

0. 3

0. 4

0. 5

0. 6

0 0 .01 0 .02 0 .03 0 .04 0 .05 0 .06

Strain

S

tr

e

Result :

Thickness (mm) Youngs Modulus (N/mm 2) Yield Stress (N/mm 2) 1.76 2.1x10 5 357.17

Test Section:

The program involved fabrication of four specimens of Long column webstiffened rack section with open cross section of various thickness 1mm, 1.2mm, 1.6mm &2mm respectively are as listed below.

Section DimensionsSpecimen

NoLength(L)mm A(mm) B(mm) C(mm) D(mm) E(mm)

Thick (t in mm)

Section - 1


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1 2000 60 60 15 10 14.1 12 2000 60 60 15 10 14.1 1.23 2000 60 60 15 10 14.1 1.64 2000 60 60 15 10 14.1 2 Section - 2

1 2000 60 60 15 20 21.2 12 2000 60 60 15 20 21.2 1.23 2000 60 60 15 20 21.2 1.64 2000 60 60 15 20 21.2 2

2.2 Test Set up & Instrumentation:

The experimental arrangements are shown in Fig. below.


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Initial arrangements

L Angle arrangements for Translation resistance

Test Procedure:

1.The test specimen has been fixed in to the test setup as shown in fig. above, by the

use of corner L angle, used for free rotations (i.e. moment free) and completely

avoiding the translation of the member.

2.Check the alignments and fix the LVDT (for testing the deflection) & Strain

gauges

(for measuring strain) at a necessary locations.

3.The load cell are fixed between the Proving ring & the support and connected it in

to

the Data logger.

4.Apply axial Uniformly Distributed load, by the use of mechanical Screw Jack.

5.Necessary readings are taken from Proving ring & from the Data Logger.

6.Graphs are plotted as from the results obtained.


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7.Calculations are made theoretical (as per codes & from Literatures) and

comparing

with experimental results.8.The Experimental results also be compare with the Numerical results (By Finite

Element method as done by using ANSYS (Analytical Systems) Software.

3. Comparison of Experimental Test Results with ANSYS software:

Mode of failure in buckling for 1mm thickness specimen


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Mode of failure in buckling for 1.2mm thickness specimen

Mode of failure in buckling for 1.6 & 2mm thickness specimen


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Buckling mode failure prediction in ANSYS Software

Stress behavior of specimen by ANSYS Package

Comparison of Experimental Test Results with Numerical Analysis (as per IS 801

1975):

Specimen No Area in mm2Experimental

Ultimate Load in NTheoretical

Permissible Load in N

Specimen - 1 1 308.2 15050 169772 369.84 17038 222103 493.12 32522 330104 616.4 58891 54118

Specimen - 2 1 332.4 17283 169672 398.88 17283 22193

3 531.84 30226 329794 664.8 61971 54029

3.1 Comparison

As compare to the Experimental test results with Theoretical analysis the followingvariation has been encountered:-


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The maximum permissible load found in Numerical analysis (as per IS 801 1975) isapproximately same for 1.6mm thick of 2000mm length column as found in

experimental ultimate load, but for the sections of thickness 1mm & 1.2mm is muchhigher and for 2mm thick column is much lesser.

It is to give for the further study regarding the Numerical analysis in Long Column.

4. Conclusion

Load carrying capacity should decreases with increase in Length and Width toThickness (W/t) ratio.

Due to minimum thickness of cold rolled steel, considering the Local, torsional &distorsional buckling characteristics for its behavior study.

The ultimate compressive strength test is used to check the yield point for qualitycontrol purpose and compression test determines the compressive yield points.

if the failure is occur in the distorsional mode then the elastic distorsional stress isused to predict the ultimate strength.

For light gauge plate elements, the buckling occurs at low stresses resulting due tocompression or bending or bearing.

The ultimate strength is many times more than the critical stress, because of its post buckling strength.

Most of the failures occurs at 1/3 distance for 1, 1.2mm elements & at centre for 1.6,2mm elements.

From the experimental investigation 2mm thick cold formed steel Long columnwith Web Stiffened is preferable for C - Section .

5. Reference

1. Ben Young and Gregory J. Hancock.[2002], Tests of Channels Subjected toCombined Bending and Web Crippling, Journal of structural engineering March (2002).

2. Ben Young,[2004] Tests and Design of Fixed-Ended Cold Formed Steel Plain Angle

Columns, Journal of structural engineering ASCE / December (2004) 1931-1940.3. Ben Young, and Ehab Ellobody,[2005] Buckling Analysis of Cold-Formed SteelLipped Angle Columns, journal of structural engineering, October (2005) 1570-1579.

4. By Byoung Koo, Leeand Suk Ki Km[2006], Elasticas and Buckling Loads of Shear Deformable Tapered Columns with Both Hinged Ends, KSCE Journal of CivilEngineering, Vol. 10, No. 4 (2006) 275-281.

5. Rahai A.R., Kazemi. S,[2006] Buckling analysis of non-prismatic columns based onmodied vibration modes, Department of Civil Engineering, Amirkabir University of Technology Available online 22 December (2006).


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6. Ben Young, Experimental Investigation of Cold-Formed Steel Lipped AngleConcentrically Loaded Compression Members.

7. Demao Yang, Gregory J Hancock,[2003] Compression Tests of Cold-Reduced High

Strength Steel Channel Columns failing in the Distortional Mode, Centre for AdvancedStructural Engineering January (2003).

8. Schafer B. W.,[2002] Local, Distortional, and Euler Buckling of Thin-WalledColumns, Journal Of Structural Engineering March (2002) 289 299.

9. Talikoti1R.S, Bajoria K.M.,[2005] New approach to improving distortional strength of intermediate length thin-walled open section columns, Electronic Journal of StructuralEngineering, 5 (2005)

10. Vaidotas apalas, Michail Samofalov, Viaeslavas arakinas,[2005] FemStability Analysis Of Tapered Beamcolumns, Journal Of Civil Engineering AndManagement (2005),Vol Xi,No.3.

comp test on c section

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