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INTERNATIONAL JOURNAL OF APPLIED ENGINEERING RESEARCH, DINDIGUL Volume 1, No1, 2010

© Copyright 2010 All rights reserved Integrated Publishing Association

RESEARCH ARTICLE ISSN 09764259

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Investigation on Cold formed C section Long Column with Intermediate Stiffener & 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]

AbstractThe Present thesis work aims at the study of buckling behavior of open web

Open cross section with intermediate stiffener & corner Lips under compression. Introduction deals with the general idea about cold formed steel members, problems on investigation need 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 and Open web sections. Expressions for distortional buckling stress & flexural torsional buckling stress has been obtained for mono symmetric open cross section compression members. Four test specimens have been fabricated with geometry of C Section with stiffened both Web and Flange with various thickness and experimented. Numerical analysis using FEM Software ANSYS 11 is performed on the tested models and the results are compared with the Experimental results. Design for maximum Limit strength of Columns using Indian Standard (IS 801 1975) is to be calculated.

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

1.Introduction

Coldformed steel products are found in all aspects of modern life; in the home, the shop, the factory, the office, the car, the petrol station, the restaurant, and indeed in 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 a tremendous diversity of shapes, sizes, and applications are produces in steel using the cold forming process.

Coldformed steel products such as sections have been commonly used in the metal 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 strengthto weight ratios. In market various shapes of these products are available Csections 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 forming steel sections in a cold state (i.e. without application of heat) from steel sheets of uniform thickness.

The use of coldformed 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 thinwalled sections by the coldforming process. They are commonly called “Light gauge sections” since their thickness has been normally less than 2.0 mm. However, more recent developments have allowed sections up to 25 mm to be coldformed, and open sections up to approximately 8mm thick are becoming common in building construction. The steel used for these sections may have a yield stress ranging from 250 MPa to 550 MPa. The higher yield stress steels are also becoming more common as steel manufacturers produce high strength steel more efficiently.

Further, the shapes which can be coldformed are often considerably more complex than hotrolled steel shapes such as Isections and unlipped channel sections. The cold formed sections commonly have mono symmetric or point symmetric shapes, and normally have stiffening lips on flanges and intermediate stiffeners in wide flanges and webs. Both simple and complex shapes can be formed for structural and nonstructural applications as shown in Figure. Special design standards have been developed for these sections.

The market share of coldformed structural steelwork continues to increase in the developed world. The reasons for this include the improving technology of manufacture and corrosion 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 coldformed steel sections specifically as loadbearing structural components 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, Office equipment, 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 strainhardening range. These increases are predominant in zones where the metal is bent by folding. The effect of cold working is thus to 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, coldformed 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 Pregalvanized or precoated metals can be formed, so that high resistance to corrosion, besides an attractive surface finish, can be achieved.

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

v High strength to weight ratio is achieved in coldrolled products. v They are usually light making it easy to transport and erect v 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 strengthtoweight ratios can be obtained.

v Load carrying panels and decks can provide useful surfaces for floor, roof, and wall 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 supporting members.

1.2 Characteristics Of Cold Formed Steel Structural Members

v Compared with other materials such as timber and concrete, the following qualities can be realized for coldformed steel structures members.

v Lightness v High strength and stiffness v Ease of prefabrication and mass production v 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 to fail flexural buckling, or flexural – torsional buckling depending on their actual sizes. Double symmetrical 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) and torsional buckling (T). Long columns fail in flexural or flexural – torsional buckling and short columns in distorsional buckling.

1.4 Types of Buckling

i) Local Buckling ii) Distorsional Buckling iii) Euler’s buckling (Flexural or flexural – torsional)

1.5 Local Buckling:

The plate elements of Cold – formed sections are normally thin higher plate slenderness ratio and hence they buckle locally before yield stress is reached, Local buckling mode 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 does not immediately lead to failure. The elements can carry additional load in the post – buckling strength before failure occurs. The Post – buckling strength of elements having relatively large 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 will undergo flexural buckling along half wave lengths.

1.7 Torsional Buckling:

In the Torsional buckling mode, the members fails by twisting about the longitudinal axis 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 in numbers with edge stiffened elements. In members with intermediate stiffened elements distorsional buckling is characterized by displacement of the intermediate stiffener normal to the plane of the element.

2. Experimental Study:

To get insight of the behaviour and the mode of failure of C section Column of Open Cross section with Web Stiffened – Under Compression.

Properties of Specimen:

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

Tension Test on Steel Sheet:

IS 1608 – 2005 (Part – I) prescribes the method of conducting tensile test on steel sheet 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 piece may 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 transition radius 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 than 40mm. alternatively; the test piece may consist of a strip with parallel sides.

v The ends of the test piece metal held in suitable grips in the testing machine in such 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 length Le = Parallel length Lt = 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 so regulated 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 Young’s modulus and the Yield stress were calculated.

Load in KN Deflection in mm Stress in N/ mm2 Strain

0 0 0 0 0.9 0.009 0.035714286 0.0001 1.8 0.023 0.071428571 0.000256 2.7 0.0276 0.107142857 0.000307 3.6 0.0437 0.142857143 0.000486 5.4 0.06325 0.214285714 0.000703 6.3 0.069 0.25 0.000767 7.2 0.07245 0.285714286 0.000805 8.1 0.08855 0.321428571 0.000984

9.3885 0.09545 0.372559524 0.001061 9.7455 0.2944 0.38672619 0.003271 10.8 0.3887 0.428571429 0.004319

10.8157 0.4025 0.429194444 0.004472 10.155 0.7935 0.40297619 0.008817




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11.43 1.0005 0.453571429 0.011117 11.745 1.2075 0.466071429 0.013417 12.165 1.8124 0.482738095 0.020138 12.73125 2.093 0.505208333 0.023256 12.8625 2.4025 0.510416667 0.026694 13.25625 2.9877 0.526041667 0.033197 13.335 3.3005 0.529166667 0.036672 13.335 3.7007 0.529166667 0.041119 11.85 3.77775 0.470238095 0.041975 11.27 4.002 0.447222222 0.044467 10.8 4.0825 0.428571429 0.045361 10.26 4.2205 0.407142857 0.046894 9 4.4137 0.357142857 0.049041

7.4835 4.7173 0.296964286 0.052414 6.9 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 s

Result:

Thickness (mm) Young’s 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 web stiffened rack section with open cross section of various thickness 1mm, 1.2mm, 1.6mm & 2mm respectively are as listed below.

Section Dimensions Specimen

No Length (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 1 2 2000 60 60 15 10 14.1 1.2 3 2000 60 60 15 10 14.1 1.6 4 2000 60 60 15 10 14.1 2 Section 2 1 2000 60 60 15 20 21.2 1 2 2000 60 60 15 20 21.2 1.2 3 2000 60 60 15 20 21.2 1.6 4 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 mm2 Experimental

Ultimate Load in N Theoretical

Permissible Load in N

Specimen 1 1 308.2 15050 16977 2 369.84 17038 22210 3 493.12 32522 33010 4 616.4 58891 54118

Specimen 2 1 332.4 17283 16967 2 398.88 17283 22193 3 531.84 30226 32979 4 664.8 61971 54029

3.1 Comparison

As compare to the Experimental test results with Theoretical analysis the following variation has been encountered:




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ü The maximum permissible load found in Numerical analysis (as per IS 801 – 1975) is approximately 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 much higher and for 2mm thick column is much lesser.

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

4. Conclusion

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

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

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

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

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

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

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

ü From the experimental investigation 2mm thick cold formed steel “Long column with Web Stiffened” is preferable for “C Section”.

5. Reference

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

2. Ben Young,[2004] “Tests and Design of FixedEnded Cold Formed Steel Plain Angle Columns”, Journal of structural engineering © ASCE / December (2004) 19311940.

3. Ben Young, and Ehab Ellobody,[2005] “Buckling Analysis of ColdFormed Steel Lipped Angle Columns”, journal of structural engineering, October (2005) 15701579.

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 Civil Engineering, Vol. 10, No. 4 (2006) 275281.

5. Rahai A.R., Kazemi. S,[2006] “Buckling analysis of nonprismatic columns based on modified 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 ColdFormed Steel Lipped Angle Concentrically Loaded Compression Members”.

7. Demao Yang, Gregory J Hancock,[2003] “Compression Tests of ColdReduced High Strength Steel Channel Columns failing in the Distortional Mode”, Centre for Advanced Structural Engineering – January (2003).

8. Schafer B. W.,[2002] “Local, Distortional, and Euler Buckling of ThinWalled Columns”, Journal Of Structural Engineering March (2002) 289 – 299.

9. Talikoti1R.S, Bajoria K.M.,[2005] “New approach to improving distortional strength of intermediate length thinwalled open section columns”, Electronic Journal of Structural Engineering, 5 (2005)

10. Vaidotas Ðapalas, Michail Samofalov, Viaèeslavas Ðaraðkinas,[2005] “Fem Stability Analysis Of Tapered Beamcolumns”, Journal Of Civil Engineering And Management (2005),Vol Xi,No.3.

investigation on cold ­ formed c ­ section long column ... · pdf filev termite proof...

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investigation on cold formed c section long column ... · pdf filev termite proof...