Finite Element Analysis of Floor Deck Using Cold Formed Steel

Transcription

1 Finite Element Analysis of Floor Deck Using Cold Formed Steel Bismi Shajahan 1, Remya Raju 2 1, 2 Department of Civil Engineering, Ilahia College of Engineering & Technology, Mulavoor, Kerala, India Abstract The design and development of new cold formed steel products can incur significant cost and the product may not be optimized for either performance or manufacture. This study describes the profile of a cold formed steel section and deck using a combined approach of finite element analysis and optimization techniques. To illustrate the concept, the design and development of a floor deck in the form of a sandwich panel, which is subjected to bending is presented. The performance of cold formed products is achieved by increasing the strength of the product without increasing the amount of the material used. The results of this project clearly demonstrate an efficient configuration of cold formed steel floor deck. Keywords Cold formed steel, cold formed steel structural members, cfs sections, cfs decks, single panel decks, double panel decks. I. INTRODUCTION Cold-formed steel (CFS) structures are structures composed of structural sections formed by folding at ambient temperature without any heat treatment. They are normally thin walled but sections up to 25-mm thick are now being cold-formed from plate and strip. The usual manufacturing process is by roll forming where coil steel passes through a series of rollers which progressively form the desired shape. Traditionally, simple channels (Cs), zeds (Zs), hat sections and decking have been used mainly in roof and wall systems, steel storage racks, steel-framed houses (residential) and many other similar secondary applications. However, the sections are now being used more commonly in primary structures such as portal frames and floor systems. Cold-formed steel (CFS) cross-sections are used extensively in the construction industry as secondary loadcarrying members, such as roof purlins and wall girts. In recent years, however, CFS cross-sections are also increasingly being employed as primary structural elements. For example, CFS framing systems are used in low-to mid-rise multi-storey buildings and CFS portal frames are gaining popularity in single-storey industrial buildings with short to intermediate spans. In both cases, CFS members are employed as the primary load-bearing members and consequently have to meet increased demands in terms of span length and loadcarrying capacity. Compared to hot-rolled member, CFS thinwalled members offer several advantages of economy and efficiency, including a high strength for a light weight, a relatively straight forward manufacturing process and an ease of transportation and erection. Above all, CFS sections offer flexibility and versatility in producing a variety of crosssectional shapes, which are obtained by bending relatively thin metal sheets using either a cold-rolling or a press-braking process at room temperature. The flexibility of the manufacturing process in obtaining various shapes means that there is a great potential for CFS sections to be optimized to meet specific objectives, there by bringing practical benefits to both manufacturers and structural designers. Cold-Formed Steel Structural Members: The idea behind cold-formed steel members is to use shape rather than thickness to support load. Due to the relatively easy method of manufacturing, a large number of different configurations can be produced to fit the demands of optimized design for both structural and economical purposes. Fig. 1 shows typical coldformed steel shapes. Fig. 1. Cold formed steel shapes. Cold Formed Steel Floor Deck: Cold-formed steel decks are widely used in commercial and institutional building construction. They are made by forming cold-formed steel sections into profiles, which greatly increases the bending capacity of the sheet steel and results in a very high strengthto-weight ratio. One of the great advantages of using steel deck in building construction is that it can function as a working platform and serve as a stay-in-place form that carries construction loads and concrete weight during construction, and as a permanent part of load resistance system in service. II. Fig. 2. Cold formed steel floor deck. GEOMETRY OF CFS SECTIONS AND CFS DECKS The dimensions of the cold formed steel sections considered in this study were fixed with reference to the code 251

2 IS 811:1987. The amount of steel material is kept same for all models. The steel sections considered are, Lipped C-Section, Lipped Z-Section and Hat Section. Fig. 6. Lipped Z-Section. Fig. 3. CFS-sections. TABLE I. Geometry of cfs-sections. Description Values Web height 100 mm, 70 mm (hat) Flange width 40 mm Lip height 20 mm Thickness of the section 2mm Length of the section 1000 mm Boundary condition Fully wrapped Length of the end plate 100 mm, 70 mm (hat) Thickness of the end plate 5 mm Support condition Simply supported Loading condition Two point loading The configurations of steel deck considered are, (i) Type I Single panel (ii) Type II Single panel (iii) Type III- Double panel (iv) Type IV- Double panel (v) Type V- Double panel Fig. 7 Hat Section Fig. 8. Type I single panel deck. Fig. 9. Type II single panel deck. Fig. 4. CFS-decks. TABLE II. Geometry of cfs-decks Description Values Length of the deck panel Width of the deck panel Height of the deck panel Support condition Loading condition 1000 mm 760 mm 100 mm Simply Supported Two point loading Fig. 10. Type III double panel deck. III. MODELING Fig. 11. Type IV double panel deck. Fig. 5. Lipped C-section. 252

3 CFS-decks: Fig. 12. Type IV double panel deck. III. ANALYSIS OF THE MODELS The results of the non-linear static structural analysis of the cold formed steel sections and cold formed steel decks are given below. CFS-sections: Fig. 16. Deformed shape of type I single panel deck. Fig. 13. Deformed shape of lipped C-section. Fig. 17. Deformed shape of type II single panel deck. Fig. 14. Deformed shspe of lipped Z-section. Fig. 18. Deformed shape of type III double panel deck. Fig. 15. Deformed shape of Hat section. TABLE III. Analysis results of sections Sections Deflection (mm) Load Capacity (kn) Lipped C Lipped Z Hat Fig. 19. Deformed shape of type IV double panel deck. 253

4 Fig. 23. Stress acting on the middle plate of Type III Double panel Deck. Decks Fig. 20. Deformed shape of type V double panel deck. TABLE IV. Analysis results of single panel decks Deflection (mm) Load Capacity (kn) Moment Capacity (knm) Stress acting in the Middle section (N/mm 2 ) Type I Type II Decks TABLE V. Analysis results of double panel decks Load Moment Deflection Capacity Capacity (mm) (kn) (knm) Stress coming on the Middle section(n/mm 2 ) Type III Type IV Type V The Deck IV is having low capacity to carry load as it fails due to tension in the middle plate. Fig. 24. Stress acting on the middle plate of Type IV Double panel Deck. V. RESULT AND DISCUSSION In single deck configurations, Deck I is showing good performance than the Deck II. The capacity of the Deck I is due to the higher stiffness at the middle section of the panel. Fig. 25. Stress acting on the middle plate of Type V Double panel Deck. Fig. 21. Stress acting on the middle section of Type I Single panel Deck. Fig. 22. Stress acting on the middle section of Type II Single panel Deck. The load capacity of Deck V is reduced due to the compression failure of the middle plate because of the uneven spacing between the sections in the lower panel. VI. RECTIFICATION From the analysis, it is clear that the Deck IV and Deck V are failed patterns, due to the insufficient capacity to take loads and stress coming over on it. So these configurations are rectified by changing the configuration pattern of the lower panel as shown in the fig. No 25 and fig.no.28. The rectified pattern of Type IV Double panel Deck is named as Type VI Double panel Deck. And Type V Double panel Deck is named as Type VII Double panel Deck. In double deck configuration, Deck III is showing high performance than Deck IV and Deck V. The capacity of the Deck III is due to the capacity of the sections achieved by the uniform spacing of the sections and the capacity of the middle plate. 254

5 Fig. 26. Configuration of deck VI. Fig. 31. Stress acting on the middle plate of Type VI Double panel Deck. TABLE VI. Analysis results of type VI and VII double panel decks. Decks Load Moment Stress coming Deflection Capacity Capacity on the Middle (mm) (kn) (knm) section(n/mm 2 ) Type VI Type VII Fig. 27. Deformed shape. Fig. 28. Stress acting on the middle plate of Type VI Double panel Deck. Fig. 29. Configuration of deck VII. Fig. 30. Deformed shape. So the reduced load capacity in the decks can be improved by providing the same configuration of sections on the both upper and lower panel or by increasing the thickness of the middle plate. VII. CONCLUSIONS Among the three different sections lipped C-section showed slightly better performance than other two sections by keeping the amount of material same. So Lipped C-section is chose for developing different configurations of cold formed steel decks. The ultimate strength (load capacity) of each case is identified from the stress-strain curve plotted with the results of analysis. Among the two single panel deck configuration, Type I Single Panel Deck is showing better performance than Type II single panel deck. Among the three double panel deck configuration, Type III double panel deck is having high capacity to withstand the load coming over on it. Double panel decks with same configuration of sections on the upper and lower panel is showing almost same result. That means a double deck which is formed by the assemblage of same configuration at the upper and lower panel will show always good result than different panel configuration at top and bottom. Among Type III, Type VI and Type VII double panel floor decks, all of them showing almost same result but the Type VI Double Panel Deck is having little more load capacity than others. By comparing single panel deck and double panel deck, it can be easily understood that, a double panel floor deck is more capable of taking load and showing good performance than single panel floor deck with same pattern of configurations. Likewise it is predictable that triple deck pattern will show more results than single deck and double deck. But it is not advisable due to the high fabrication cost, labor charges and difficulty in installation process. 255

6 Therefore it can be concluded that, Type I Single Panel Floor Deck and Type VI Double Panel Floor Deck are the good configurations. REFERENCES [1] G J Hancock, Cold-formed steel structures: Research review , Advances in Structural Engineering, vol. 19, issue 3, pp. 1-16, [2] B. W. Schafer, Review: The Direct Strength Method of Cold-Formed Steel Member Design, Stability and Ductility of Steel Structures, [3] A. Bayan, S. Sariffuddin, and O. Hanim, Cold formed steel joints and structures -A review, International Journal of Civil and Structural Engineering, vol. 2, no. 2, pp , [4] B. P. Gilbert, T. J.-M. Savoyat, and L. H. Teh, Self-Shape optimisation application: Optimisation of cold-formed steel columns, Thin-Walled Structures, vol. 60, pp , [5] P. S. Ajay, Flexural behaviour of cold formed steel beams with diagonal stiffener, International Journal of Engineering Trends and Technology, vol. 17, no. 8, pp , [6] A. Dandens, J. Kreilis, and G. Andersons, Properties of cold-formed steel sections, Materials and Structures, [7] M. MacDonald and M. P. Kulatunga, Finite element analysis of cold formed steel structural members with perforations subjected to compression loading, Mechanics and Mechanical Engineering, vol. 17, no. 2, pp ,