FLEXURAL BEHAVIOUR OF COLD FORM STEEL SECTIONS SUBJECTED TO STATIC LOADING

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1 International Journal of Civil Engineering and Technology (IJCIET) Volume 9, Issue 3, March 2018, pp , Article ID: IJCIET_09_03_097 Available online at ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed FLEXURAL BEHAVIOUR OF COLD FORM STEEL SECTIONS SUBJECTED TO STATIC LOADING Sivaranjani.S, Nalini.S and Annapurani.M Assistant Professor, Department of Civil Engineering, Vel Tech Dr RR & Dr SR University, Chennai, Tamilnadu, India ABSTRACT At present, Cold Formed Steel (CFS) sections such as C and Z sections are commonly used in structural forming. But they suffer from certain buckling modes in open sections primarily due to flexural buckling. It is therefore important that these buckling modes are either delayed or eliminated to increase the ultimate load carrying capacity of these members. For this purpose hat section is suggested here and the strength performance of hat section is compared with channel section. In the present study the flexural behaviour of Cold Formed Steel hat section and channel section beams subjected to midpoint static loading is analyzed using Finite Element Analysis (FEA). For this purpose a specimens of 1m length and 4mm thickness is investigated for the buckling performance. This buckling performance is carried out by ANSYS 10.0 software and the results of both sections are compared with the experimental test done in UTM. Keywords: Cold formed steel, flexural buckling, Finite Element Analysis, ANSYS. Cite this Article: Sivaranjani.S, Nalini.S and Annapurani.M, Flexural behaviour of Cold Form Steel Sections Subjected to Static Loading, International Journal of Civil Engineering and Technology, 9(3), 2018, pp INTRODUCTION Cold-formed steel is the common term for products made by rolling or pressing thin gauges of sheet steel into goods. Cold-formed steel goods are created by the working of sheet steel using stamping, rolling or presses to deform the sheet into a usable product. The light gauge steel members are defined as structural members cold- formed to shape in rolls or press-braked steel sheets or strips or plates or flats. The strength of elements used for design is usually governed by buckling. They are commonly called Light gauge sections since their thickness has been normally less than 12.0 mm. However, more recent developments have allowed sections up to 25 mm to be cold formed, 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 yield value is increased by 15%-30% due editor@iaeme.com

2 Sivaranjani.S, Nalini.S and Annapurani.M to prework (initial deformation) [1]. The higher yield stress steels are also becoming more common as steel manufacturers produce high strength steel more efficiently. CFS members are commonly used as purlins, cladding rails, sheeting rails, wall studs, floor joists, sheet sand decks, etc. in the building industry. Some of the qualities of these members that create cost savings in construction are light in weight, high strength and stiffness, accurate section dimensions, and easy of prefabrication and mass production [2]. In market various shapes of these products are available C, Z and hat sections are predominantly used in light load and medium span situations such as roof systems. Today cold-formed steel sections finds many applications in different types of industries, various types of equipments, construction of car and Motor vehicle bodies, railway coaches, storage racks, highway products and Bridge construction. 2. PRELIMINARY TEST The development of an appropriate analytical model to predict the behavior of Cold-Formed Steel (CFS) structural members requires a correct representation of the corresponding material characteristics. Hence it is essential to find out the mechanical properties of the CFS steel sections. For this a test named Coupon Test is carried out here. The tensile coupons consisted of 2 standard flat coupons, length 180mm width 25mm. The standard flat coupons were dimensioned according guidelines provided by IS 1608:2005 and ISO 6892:1998, Metallic materials Tensile Testing at Ambient Temperature. The tensile coupons were tested in a KN UTM machine. The coupons were mounted in the testing machine using the gripping devices and aligned with vertical axis of the machine. The axial load was applied at a constant rate and the values are noted and the stress values are tabulated. As a resulting Engineering stress-strain curves are drawn. A. Coupon Specimens Before Test After Test B. Coupon Test Data: Length of plate =180mm Width of plate = 25mm Thickness of plate = 4mm Cross section area = 100mm 2 Figure 1 Coupon test specimens editor@iaeme.com

3 Flexural behaviour of Cold Form Steel Sections Subjected to Static Loading Young's modulus 'E'x10 5 (Mpa) Table 1 Coupon Test 1 Load (kn) Stress (mpa) Strain Table 2 Coupon Test Load (kn) Stress (mpa) Strain Table 3 Coupon Test Results f y (Mpa) (0.1 %) f y (Mpa) (0.2%) Yielding Type G G *G- Good yielding 3. NUMERICAL INVESTIGATION The Finite Element Method (FEM) (its practical application often known as Finite Element Analysis (FEA) is a numerical technique for finding approximate solutions of partial differential equations (PDE) as well as integral equations. In FEA, a complicated structure is divided into smaller elements. Each element is based on physical laws using numerical computing techniques. All the elements are assembled into a big matrix of algebraic equations. This matrix is usually solved by computer. Finally, the solution is obtained according to the Engineer s requirements. A. ANSYS Programme ANSYS is a commercially available finite element analysis software package for FEA. The finite element program of ANSYS 10.0 workbench version is used to develop a finite element model, which aimed to simulate the behaviour and strength of the cold-formed steel C and hat sections. B. Boundary Conditions The specimens of 1m length and 4 mm thickness of channel and hat sections are modeled and analysed for the strength performance. It was found that good simulation results could be obtained by using the element (mesh) size of approximately 2.5x2.5 mm (length by width) for the web, flanges and lips. The ends of the specimens are simply supported with hinges and rollers. The bearing length of 100mm is kept on either side of the specimen editor@iaeme.com

4 Sivaranjani.S, Nalini.S and Annapurani.M C. Static analysis of Channel Section D. Static Analysis of Hat Section Figure 2 At the load of 49kN Figure 3 At the load of 59kN 4. EXPERIMENTAL INVESTIGATIONS In order to investigate the flexural-buckling performance of cold-formed steel sections (CFS) UTM is used here. The main aim of our experiment is to find the load carring capacity of the beams and secondly to measure the vertical and horizontal deflections and to draw loaddeflection graphs. A. Materials Used Figure 4 Before & After painting editor@iaeme.com

5 Flexural behaviour of Cold Form Steel Sections Subjected to Static Loading B. Methodology The beams are prepared initially. It is ensured that the steel beams are of free from rust and painted for getting the clear view of deflection and all. The schematic procedure of the experiment of CFS beams for buckling of beam is as follows. Initially the beam is placed in the UTM machine with its position. Strain variations in the cross section is observed at midpoint of the beam, We do the measurement at mid-span and the strain gauges are fixed in the vertical and lateral direction to beam. The strain indicators can be fine-tuned for zero at starting. Similarly auto adjustments for deflection measurements are made. Now, loading is done and deflections are tabulated Similarly the experiment is repeated with increment of loads and the readings are tabulated. It is continued until the beam fails and the final load is noted. Figure 5 Before & After loading - Channel section C. Flexural tests on CFS Sections Figure 6 Before & After loading - Hat section 1. Flexural tests on CFS C Channel Section Data: Depth of web (h w ) = 94mm Breadth of flange (b f ) = 52mm Thickness of plate (t) = 4mm Span (L) = 1000mm Moment of inertia (I x ) = 2.1 x 10 6 mm 4 Section modulus (Z x ) = 1.3 x 10 5 mm editor@iaeme.com

6 Sivaranjani.S, Nalini.S and Annapurani.M S.No Table 4 Deflection Measurement Load (kn) Deflection Measurements (mm) Vertical Lateral 1 10 (min) (middle) (max) Figure 7 Load vs Vertical Deflection From this graph we can say that the vertical deflection of the section is deeply increasing from 20kN to 25kN. Final vertical deflection is of 27mm. Figure 8 Load vs Lateral Deflection The lateral deflection of the section starts from 5kN and increasing deeply from 35kN to 40kN. Final lateral deflection is 12mm. 2. Flexural tests on CFS Hat Section Data: Depth of web (h w ) = 94mm Breadth of flange (b f ) = 52mm Depth of lip (d 1 ) = 32mm Thickness of plate (t) = 4mm Span (L) = 1000mm Moment of inertia (I x ) = 1.53 x 10 6 mm 4 Section modulus (Z x ) = 1.6 x 10 5 mm editor@iaeme.com

7 Flexural behaviour of Cold Form Steel Sections Subjected to Static Loading S.No Table 5 Deflection measurement Load (kn) Deflection Measurements (mm) Vertical Lateral 1 15 (min) (middle) (max) 33 8 Figure 9 Load vs Vertical Deflection The response to the load given by hat section starts from 10kN. A constant deflection occurred in the load range of 27kN. 34mm is the final vertical deflection. Figure 10 Load vs lateral deflection The hat section shows its lateral deflection from 10kN. A constant deflection is occurred in the loads of 50kN to 60kN. Overall lateral deflection is 8 mm. 5. DISCUSSIONS Descriptions Table 6 Comparision table Channel section Hat section Dimension(mm) 94 x 52 x 4 94 x 52 x 32 x 4 Load Bearing Capacity (kn) Vertical deflection Lateral deflection Min(mm) 4 2 Max(mm) Min(mm) 2 2 Max(mm) editor@iaeme.com

8 Sivaranjani.S, Nalini.S and Annapurani.M From this table VI, we can say that, the hat section takes 41% more load than that of channel section. The ability of resistance against vertical loading in hat section is 42% more than the channel section. Also hat section shows 50% resistance against lateral deflection than the channel section. 6. RESULTS It is clear that the hat section is stable against more load than the channel section. Deflection occurred in the hat section is less than the channel section. While considering both vertical and lateral deflection, lateral deflection is less than that of vertical deflection in HAT and CHANNEL section. But the cost of making of hat section is more the channel section. Apart from this cost consideration hat section is quite sound than channel section. REFERENCES [1] M.S. Deepak, R. Kandasamy and R. Thenmozhi, Investigation On Lateral- Torsional Buckling Performance Of Cold Formed Steel C Channel Sections. International Journal of Emerging Trends in engineering and development, Issue 2, vol. 4 (2012). [2] Wen Yu Wei, Cold Formed Steel Structures Design and Analysis Construction, Tata Mc craw Hill Book Company (2002). [3] Asim Kasim and Hojiat Adeli, Global Optimum Design of Cold Formed Steel Hat- Shape Beams, Thin Walled structure (1999). [4] P.Avery, M. Mahendren and A. Nasir, Flexural Capacity of Hollow Flange Beams, Journal of Construction Steel Research (2000). [5] M. Bogdan Put, Yong-Lin Pi and N.S. Trahair, Lateral Buckling Tests on Cold Formed Channel Beams. Structural Engineering, pp 125 (2011). [6] B. Gangadhara Prusty Free Vibration and Buckling Response of Hat- Stiffened Composite Panels under General Loading. International journal of mechanical science, Vol.50 (2008). [7] Haming wang, Yaochun Zhang, Experimental and Numerical Investigation of C-section Flexural Members. Constructional Steel Research (2009). [8] G.J Hancock, Cold-Formed Steel Structures. Journal of Constructional Steel Research (2003). [9] IS Code of Practice for Use of Cold-Formed Light Gauge Steel Structural Members in General Building Construction. [10] IS Code of Practice for General Construction in Steel editor@iaeme.com