Behaviour and Design of Light Gauge Cold Formed Steel Flexural Members(Comparison of Channel

Behaviour and Design of Light gauge Cold Formed Steel Flexural Members(Comparison of Channel and Built up Channel Section)

A Jayaraman1 V Senthilkumar2 S Athibaranan3

1 Assistant Professor, Department of Civil Engineering Bannari Amman Institute of Technology, Sathamangalam-638401, India.

2 Assistant Professor (Sr. G), Department of Civil Engineering Bannari Amman Institute of Technology, Sathamangalam-638401, India.

3 Assistant Professor, Department of Civil Engineering Bannari Amman Institute of Technology, Sathamangalam-638401, India

Abstract

Cold formed steel members are extensively used in the building construction industry, especially in residential, commercial and industrial buildings.This paper presents a study on behaviour and economical of cold formed steel (CFS) built up channel section and channel section by same cross sectional area. This study involves in examination of theoretical and numerical investigations of specimens in series. Overall two specimens were designed and comparison of all the internal force, and hence, to evaluate the co-existing momentsand shear forces at the critical cross-section with same configuration area by keeping all other parameters constant.The theoretical data are calculated using Indian Standard code IS 801-1975 and the section properties of the specimens are obtained using IS 811-1975.The specimens are designed under uniformly distributed loading with simply supported condition.The theoretical results are verified using ANSYS V11 software. The research project aims to provide which section is economical, high bending strength, more load carrying capacity and high flexural strength. The studies reveal that thetheoretical investigations channel section have high bending strength, high load caring capacity, minimum deflection and minimum local buckling& distortional buckling compare to the built up channel section by same cross sectional area.

Key words:Cold formed steel, built up channel section,ANSYS,bending strength,deflection

I.INTRODUCTION

Light gauge steel sections are also known as cold formed steel sections. These sections are made from thin sheets of uniform thickness without the applications of heat. The thickness of the sheet used is generally between 1mm and 8mm. These types of sections are extensively used in the building industry, as purlins girts, light struts roof sheeting, and floor decking. These sections become economical for light loads and to form useful surfaces such as roof covering, wall panels. Load carrying capacity should decreases with increase in Length and Width to thickness (W/t) ratio. Due to minimum thickness of cold rolled steel, considering the Local, torsional & distortional buckling characteristics for its behaviour study most of the failures occurs at 1/3 distance for 1, 1.2mm elements & at centre for 1.6, 2mm elements. The experimental investigation 2mm thick cold formed steel “Long column with Web Stiffened” is preferable for “C Section”(1). Both their experimental and numerical investigation gives the good understanding about their buckling classes and failure modes that are possible. Using of CUFSM software was more useful in predicting the section properties of these specimens. Modal of the specimens analyzed in ANSYS V11 gives an idea that of their failure modes. Experimental results show that the failure of the section occurs mainly due to the buckling of flange plates and distortional buckling. (2).These sections are manufactured primarily by two processes. Cold rolling is used to produce more number of sections having longer length whereas press breaking is used to produce a small number of sections having shorter length. As the thickness of the light gauge section increases the variation in increase of joint strength reduces for various thicknesses of Stiffener/packing plates. For 1.2mm thick channel section it is observed that all failures are due to rupture with 3 bolts connection, and also for 1.5mm thick channel section up to 3mm thick Stiffener/Packing plate failure are due to rupture and for 4mm thick Stiffener/packing plate the failure is due to vertical shear failure along the line of vertical connection. With use of 5 mm thick Stiffener/packing plates the failure is due to block shear failure (3). Various types of section may be manufactured using light gauge steel. They includes angles, channel with and without lips, hat section lipped Z Section etc.. Cold Formed steel product such as Z-purlin has been commonly used in metal building industry more than 40 year in unites state due to their wide range of application, economy, ease of fabrication and high strength-to-weight ratios. Z- Purlins are predominantly used in light load and medium span situations such as roof systems (4). There are several failure modes among which distortional buckling is one such failure mode that affects the strength of the section. In order to assess the influence of distortional buckling, a parametric study has been conducted by varying the lip depth, which is the influencing factor for distortional buckling strength (5). Channels may be used as compression or flexural members. Hat section and Z section are used as flexural members. Hollow rectangular section used for variety of sections. Built up I section using Light gauge steel with lower H/t aspect ratio behaves significantly showing elastic and plastic deformation both. With increment in H/t aspect ratio this behaviour changes and shows failure in elastic zone(6). Black bolts and high strength friction grip bolts may be used for the connection of the light gauge sections. However, high strength friction grip bolts are most suitable for the connection of light gauge sections. Advances in computational features and software have brought the finite element method within reach of both academic research and engineers in practice by means of general-purpose nonlinear finite element analysis packages, with one of the most used nowadays being ANSYS. The program offers a wide range of options regarding element types, material behaviour and numerical solution controls, as well as graphic user interfaces (known as GUIs), auto-meshers, and sophisticated postprocessors and graphics to speed the analyses. In this paper, the structural system modelling is based on the use of this commercial software. Several numerical modelling issues related to potential convergence problems, loading strategies and computer efficiency. The accuracy and simplicity of the proposed model make it suitable to predict and/or complement experimental investigations (7) .most of structural elements are analysis by using STADD pro and ANSYS.

II. AIM OF THE STUDY

The main aim of the studyprovides which section is economical, high bending strength, more load carrying capacity and high flexural strength by analysis of theoretical and numerical investigation.

III .EXPERIMENTAL INVESTIGATION

3.1 Materials

3.1.1 Light gauge steel physical properties:The rolled steel sheet is used. Thephysical properties of light gauge steel section given in Table 1.The properties taken from the Indian Standard code IS 800-2007

Table 1. Physical properties light gauge steel section

3.1.2 Light gauge steel channel sectionproperties:The rolled steel sheet is used. The channel sectional properties of light gauge steel section (given in Table 2.The properties taken from the Indian Standard code IS 811-2007

Table 2. Properties of (60 x 30 x 1.6) light gauge steel Channel section

3.1.3 Light gauge steel built up channel section properties:The rolled steel sheet is used. The built up channel sectional properties of light gauge steel section (given in Table 3) The properties taken from the Indian Standard code IS 811-2007

Table 3. Properties of light gauge steel built up Channel section

3.2 Theoretical investigationsofchannel section30 x60 x1.6) mm

3.2.1 Slenderness ratio (λ):The Slenderness ratio value is given in table 4

Slenderness ratio (λ) =

Table 4. Slenderness ratio

The slenderness ratio for flexural member as per IS Code provide 300 mm for compression flange of a beam against lateral torsional buckling ,so in this channel section (30 x60 x1.6) mm using construction up to 3m only .

3.2.2 Bending Moment (BM) of channel section 30 x60 x1.6) mm

MaximumBending Moment = 0.6 x fy x Zxx

M = 479.7 x 103 Nmm

fy = yield stress in cold form steel

Zxx= section modulus channel section

3.2.3 Load caring capacity (p) of channel section 30 x60 x1.6) mm

Bending Moment =

Maximum Load (p) = 3.79 kN / m

3.2.4 Moment of resistance ofchannel section 30 x60 x1.6) mm

Moment of resistance (MR) = Fb x Zxx

Fb =

Fb = 154.16N / mm2

Moment of resistance (MR) = 519 x 103Nmm

Fb = basic design stress

E = young’s modulus of steel

Cb = bending coefficient

3.2.5 Shear capacity ofchannel section 30 x60 x1.6) mm

Maximum shear = = 1.89 kN / m

Maximum average shear stress = = 10.42 N / mm2

3.2.6 Allowable stresses in web of beam

Shear stresses in webs – The maximum average shear stresses (Fv), on the gross area of a flat web shall not exceed (0.4 x fy)

For

Fv = = 181.2 N / mm2

= 33.5

= 92.95

Fv = 181.2 N / mm2 > 10.42 N / mm2Hence Safe in shear

3.2.7 Combined bending and shear stress in webs: fbw’ = = 3140N / mm2

3.2.8 Bending and shear stress in webs: fbw= = 133.6 N/mm².

3140 N/mm² ˃ 133.6 N/mm². Hence safe in bending stress

3.2.9 Check for deflectionofchannel section 30 x60 x1.6) mm

The actual deflection (Δ) and Permissible deflection is given in table 5.

Actual deflection (Δ)=

Permissible deflection =

Table 5. Deflection

3.3 Theoretical investigationsof builtupchannel section30 x60 x1.6) mm

3.3.1 Slenderness ratio (λ):The Slenderness ratio value is given in table 4

Slenderness ratio (λ) =

Table 6. Slenderness ratio

The slenderness ratio for flexural member as per IS Code provide 300 mm for compression flange of a beam against lateral torsional buckling ,so in this channel section (30 x60 x1.6) mm using construction up to 2 m only .

3.3.2 Bending Moment (BM) of built up channel section 30 x60 x1.6) mm

Maximum Bending Moment = 0.6 x fy x Zxx

M = 103.917 x 104 Nmm

3.3.3 Load caring capacity (p) of channel section 30 x60 x1.6) mm

Bending Moment =

Maximum Load (p) = 0.82 kN / m

3.3.4 Moment of resistance ofchannel section 30 x60 x1.6) mm

Moment of resistance (MR) = Fb x Zxx

Fb =

Fb = 154.16N / mm2

Moment of resistance (MR) = 113 x 103Nmm2

3.3.5 Shear capacity ofchannel section 30 x60 x1.6) mm

Maximum shear = = 0.41 kN / m

Maximum average shear stress = = 0.142 N / mm2

3.3.6 Allowable stresses in web of beam

Shear stresses in webs – The maximum average shear stresses (Fv), on the gross area of a flat web shall not exceed (0.4 x fy)

For

Fv = = 181.2 N / mm2

= 33.5

= 92.95

Fv = 181.2 N / mm2 > 0.142 N / mm2Hence Safe in shear

3.3.7 Combined bending and shear stress in webs: fbw’ = = 3140N / mm2

3.3.8 Bending and shear stress in webs: fbw = = 133.6 N/mm².

3140 N/mm² > 133.6 N/mm². Hence safe in bending stress

3.3.9 Check for deflectionofchannel section 30 x60 x1.6) mm

The actual deflection (Δ) and Permissible deflection is given in table 7.

Actual deflection (Δ) =

Permissible deflection =

Table 7. Deflection

IV EXPERIMENTAL PROCEDURE

Overall two specimens were designed and comparison of all the internal force, and hence, to evaluate the co-existing momentsand shear forces at the critical cross-section with same configuration area by keeping all other parameters constant.The theoretical data are calculated using Indian Standard code IS 801-1975 recommended. The theoretical results of the channel section the bending moment, load caring capacity and moment resistance is 46 % , 21% and 21.7% higher than the built up channel section. Allowable stress in web of the beam, actual deflection and bending stress in web is same in both the section. The average shear stress is maximum in built up channel section compare than the channel section. The numerical investigations (using ANSYS) the bending moment, torsional moment, deformation and shear stress is 22.68 % ,51.30 % 25.52 % and 13.13% maximum in channel section in compare than the built channel section. The numerical result software analysis is given figure2,3,4,5,6,7,8 and figure 9. The comparison of theoretical design value is given in figure 1.

Theoretical investigationsof channel and built up channel section30 x60 x1.6)mm

Figure .1 comparison of theoretical design value channel and built up section

4.1 Numerical investigations(ANSYS)ofchannel section30 x60 x1.6) mm

Figure .2 Bending Moment (BM) of channel section 30 x60 x1.6) mm

Figure .3 Torsion Moment (BM) of channel section 30 x60 x1.6) mm

Figure .4 Total deformation of channel section 30 x60 x1.6) mm

Figure .5 Total sheer force of channel section 30 x60 x1.6) mm

4.2 Numerical investigations(ANSYS)ofbuilt upchannel section30 x60 x1.6) mm

Figure .6 Bending Moment (BM) of built up channel section 30 x 60 x1.6) mm

Figure .7 Torsion Moment (BM) of built up channel section 30 x 60 x1.6) mm

Figure .8 Total deformation of channel section 30 x60 x1.6) mm

Figure .9 Total sheer force of channel section 30 x60 x1.6) mm

CONCLUSIONS

The final results thetheoretical and investigations of channel section have high bending strength, high load caring capacity, minimum deflection and minimum local buckling & distortional buckling compare to the built up channel section by same cross sectional area. The numerical investigation of channel section is the maximum bending moment, torsional moment and deformation is higher than the built up channel section by same cross sectional area. But theoretical investigations are accuracy result.Channel section is the high moment of resistance , high load caring capacity and The slenderness ratio for flexural member as per IS Code provide 300 mm for compression flange of a beam against lateral torsional buckling ,so in this channel section (30 x60 x1.6) mm using construction up to 3m. Therefore channel section is most suitable and economical compare than the built up channel section.

REFERENCES

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