INTERNATIONAL JOURNAL OF CIVIL AND STRUCTURAL ENGINEERING Volume 2, No 2, 2011

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1 INTERNATIONAL JOURNAL OF CIVIL AND STRUCTURAL ENGINEERING Volume 2, No 2, 2011 Copyright 2010 All rights reserved Integrated Publishing services Research article ISSN Cold formed steel joints and structures -A review Faculty of Civil Engineering, Universiti Teknologi Malaysia, Skudai, Johor, Malaysia doi: /ijcser ABSTRACT Cold formed steel structures are structural products that are made by forming plane sheets of steel at an ambient temperature into different shapes that can be used to convince structural and functional requirements. In years, higher strength materials and a wider range of structural applications have caused a most important development in cold-formed steel relative to the common heavier hot rolled steel structural members. Therefore, the understanding of cold formed steel performance becomes an important issue to be studied. This paper holds three works. First, it reviews an introduction on cold formed steel structures. Second, it summarizes general design considerations of cold formed steel constructions. Finally, it offers a review on research of joints and structures for cold formed steel. Keywords: Cold formed steel, buckling, joints and structures 1. Introduction Cold formed steel sections are light-weight materials suitable for building construction owing to their high structural performance. The most common sections are lipped C and Z sections, the thickness typically ranges from 1.2 mm to 3.2 mm, and sections with yield strengths from 250 to 450 N/mm 2 are commonly available (Yu et al., 2005). The higher yield stress steels are becoming more common as steel manufacturers produce high strength steel more efficiently. In general, cold formed steel members are used as secondary members in building construction, and they are connected onto primary structural members through web cleats as pinned or moment connections, depending on the connection configuration. Over the past two decades, cold formed steel has seen increased usage as the structural frame for residential and multi-story commercial buildings due to inherent features that overcome the downsides of conventional products. Their strength, light weight, versatility, noncombustibility, and ease of production have encouraged architects, engineers, and contractors to use cold formed steel products, which can improve structural function and building performance and provide aesthetic appeal at lower cost. For typical applications of cold formed steel sections, there are many design recommendations on cold formed steel structures available such as AISI (1996), BS5950 (1998) and Eurocode 3: Part 1.3. Moreover, a number of design guides and commentaries are also available to assist structural engineers to design cold formed steel structures (Chung 1993, Hancock 1998, Lawson et al. 2002, Yu 2000). Cold formed steel members have unique structural stability issues primarily due to the large width-to-thickness comparison element ratios, which is not commonly the use with sections of hot-rolled steel. In order to enhance the practical use of light steel framing, this paper provides a brief summary on behavior of cold formed steel members and provides also a list of references and recommended readings, which is of vast interest for readers concerned to advance their understanding in this field. Received on September, 2011 Published on November

2 2. Cold Formed Steel Structures and their Applications The use of cold-formed steel members in structural framing have many advantages as listed below (Yu, 2002): Buildability: The use of prefabricate and preassembled steel works lessen site workings, material waste, and advanced quality. Speed: This system requires a shorter construction period compared to that for a conventional system. Strong and Lightweight: Steel has one of the peak strength-to-weight proportions of any building material. This steel in the foundation required and the lightness also makes for easier on-site handling. Safety: Steel's natural strength and non-combustible qualities enable light steel frame houses to defend against such destructive events as fires, earthquakes, and hurricanes. Homes can be designed to meet the highest seismic and wind load specifications in any part of the country. Figure 1: Cold formed steel framing Quality: A better quality finished house that is durable and low in maintenance. Easy to modify: Modifying can be easily skilled. Non-load bearing walls can be readily relocated, removed or altered. Design Flexibility: Because of its high strength, steel can be used in longer span lengths, presenting larger open spaces and increased design flexibility without requiring intermediate columns or load bearing walls. Recyclable: All steel products are recyclable. Since 1990, there is a growing trend to use cold-formed steel sections as primary structural members in building construction for low to medium rise residential houses and portal frames of modest span (Yu et al., 2005) as example shown in Figure 1. In tall multi-story 622

3 structures the major framing is typically of heavy hot rolled shapes and the minor elements may be of cold formed steel members such as steel joists, decks, or panels. In this case, the heavy hot rolled steel shapes and the cold formed steel sections supplement each other. 3. Common Design Considerations of Cold Formed Steel Members The use of slender material and cold-forming processes results in several design problems for cold formed steel construction dissimilar to those of heavy hot rolled steel construction. The next is a short argument of some problems usually joins in design (Yu, 2000) Buckling of Cold Formed Members The three basic buckling modes of thin-walled cold formed steel members are shown in Figure 2. Local buckling is a mode involving plate flexure alone without transverse deformation of the line or lines of intersection of adjoining plates, distortional buckling is a mode of buckling involving change in cross-sectional shape excluding local buckling, and the term global buckling embraces Euler (flexural) and lateral-torsional buckling of columns and lateral buckling of beams (Hancock, 2003). Figure 2: Examples of bending and compression buckling modes (AISI, 2004) 3.2. Torsion and Distortion Cold formed open section steel members are more expected to go through torsional deformation due to their low torsional rigidity, resulting from their slender walls. Further, the sections are often loaded eccentrically from their shear centers and so are subject to considerable torques as shown in Figure 3(a) and sometimes include distortional buckling Figure 3(b) Stiffeners in Compression Elements The load-carrying capability and the buckling performance of compression components of beams and columns can be enhanced significantly by the use of edge stiffeners or 623

4 intermediate stiffeners. Requirements for the design of such stiffeners have been developed from previous research. Nevertheless, this type of stiffener generally is not practical in hot rolled shapes and built-up members. Figure 3: Torsional and distortional buckling deformations of channel sections (Hancock, 2003) 3.4. Properties of Cold Formed Steel Sections This section having a stiffened, partially stiffened, or unstiffened compression element, the whole width of the element is fully effective when the width-to thickness proportion of the element is small or when it is subjected to low compressive stress. Nevertheless, as stress rises in the element having a reasonably large width-to-thickness ratio, the parts closest to the supported edges are more structurally effective after the plate buckles. Consequently, the stress distribution is nonuniform in the compression element. In the design of such members the sectional properties are founded based on a reduced effective area Web Crippling Web crippling frequently arises in cold formed members because they have loading eccentric from the web centerline due to the rounded corners of the sections, and because the webs are often slender and unstiffened, dissimilar to hot rolled design where web stiffeners are often used. A current paper by Young and Hancock (2001) presents experimental data on cold formed unlipped channels subject to web crippling Ductility and Plastic Design Mainly due to the sectional buckling phenomena, cold formed sections are of class 4 or class 3 as shown in Figure 4, at the most, but also due to the effect of cold-forming by stress hardening; the cold formed steel sections possess a low ductility and are not generally allowed for plastic design. Cold formed sections can be used in seismic resistant structures because there are structural benefits coming from their reduced weight, but only elastic design is allowed and no reduction of shear seismic force is possible. 624

5 Figure 4: section classifications according to moment capacity 3.7. Joints Methods for connecting cold formed members are frequently quite different from those of hot rolled members. Where welding and bolting are familiar for hot rolled members, such connection forms as screws, clinching, and riveting may be used for cold formed members. Also even for bolted connections, the structural behavior of cold formed connections is often quite different from hot rolled members due to the thin sheets and higher strength steels used (Honcock, 2003). The database used to develop specifications for the design of connections among cold formed sections is mostly based on testing a very large number of connections. These experimental works are costly and take time. They can be, at least partially, replaced by numerical models using a finite element program. Fan et al. (1997) have revealed the enormous attention of such models to advance our understanding of the real performance of the connections Thickness Limitations In the design of cold formed steel structural members, the important factors are the width-tothickness ratio of compression elements and the unit stress used; the thickness of the steel itself is not a critical factor Cold Work of Forming The mechanical properties of cold formed sections are sometimes substantially different from those of the steel sheet, strip, plate, or bar before forming. This is because the cold-forming operation increases the yield point and tensile strength and at the same time decreases the ductility. The percentage increase in tensile strength is much smaller than the increase in yield strength, with a consequent marked reduction in the spread between yield point and tensile strength. Since the material in the corners of a section is cold-worked to a considerably higher degree than the material in the flat elements, the mechanical properties are different in various parts of the cross section (Chen and Young, 2006). 625

6 4. Previous Research on Joints and structures for Cold-Formed Steel All of the connection methods appropriate to hot rolled sections are also appropriate to cold formed steel sections (Rhodes and Shanmugam, 2003). For thin sections, the main design considerations tend to be the bearing of the sections. Conventionally, connections between cold formed steel sections comprising two bolts per member are considered as shear resisting connections. Review of research on joints and structures for cold formed steel is summarized below. Chung and Lawson (2000) carried out an investigation on the structural performance of shear resisting connections between cold formed steel sections where web cleats of cold formed steel strips were used to attach beams to supporting beams and columns. A total of 24 connection tests with different fasteners (bolt, screw, and rivet) were carried out. The results were compared to design rules based on BS :1998 and EC Three modes of failure were identified: failure of fasteners, shear buckling of cold-formed steel web cleats or webs of supported beams, and lateral torsional buckling of cold formed steel web cleats. It was demonstrated that the cold formed steel web cleats might be used with bolts or self-drilling self-tapping screws as practical shear resisting connections in building construction. The rationalized usage of cold formed steel web cleats allowed simple and effective connections to be formed between cold formed steel sections leading to improved buildability. Chung and Ip (2001) established a finite element model with three-dimensional solid elements to investigate the bearing failure of cold-formed steel bolted connections under shear. The finite element package ANSYS (Version 5.3) was used to predict the structural performance of bolted connections between cold-formed steel strips and hot-rolled steel plates under shear. Three dimensional eight-noded, iso-parametric solid elements SOLID45 were employed to model all the components of a typical bolted connection, namely, the cold-formed steel strip, the hot-rolled steel plate, the bolts and also the washer, in order to capture material yielding throughout the steel thickness. It was demonstrated that the predicted load extension curves of bolted connections in lap shear tests followed closely to the measured load extension curves provided that measured steel strengths and geometrical dimensions were used in the analysis. Furthermore, it was shown that the stress strain curves, contact stiffness and frictional coefficients between element interfaces, and clamping forces developed in bolt shanks were important parameters for accurate prediction of the deformation characteristics of bolted connections. This research presented an extension of the finite element investigation onto the structural behaviour of cold-formed steel bolted connections, and three distinctive failure modes observed in lap shear tests are successfully modelled: bearing failure; the shear-out failure; and the net-section failure. Consequently, semi empirical formula for bearing resistance of bolted connections is proposed after calibrating against finite element results. A general report on the developments of cold formed steel members and structures until Year 2000 presented (Rondal, 2000). He gave particular emphases to the developments in the field of distortional buckling and improvement of new types of connections. Distortional buckling plays an important role on stability with the use of thinner sections made with high strength steel. The new theory included generalized beam theory has lead to enhanced understanding 626

7 of this complex buckling form. Researchers were investigated this issue and suggested new theory to include the distortional buckling in the design of cold formed steel flexural member. For joints between cold formed members, new joints methods have been developed for shear resisting capacity, such as press-joining and rosette joint. He concluded that the last two decade has shown large and significant growth in the facts of the performance cold formed steel members and structures by joining scientific knowledge, high strength steels, and modern design specifications. LaBoube and Soko (2002) studied the behaviour of singleshear connections using self-drilling screws in cold-formed steel construction. Fastener patterns, screw spacing, stripped screws, and the number of screws in a connection was varied to determine their influence on connection strength. A design equation was established. The findings of the research demonstrated that the screw pattern did not significantly influence the strength of the connection. However, the assumption that the connection strength for a multiple screw connection is proportional to the number of screws in the connection pattern was found to be unconservative. The connection strength decreased with decreased spacing of the screws. A stripped screw in a single shear connection did not result in the erosion of the connection strength. Chung and Ho (2005) presented an analysis and design method for lapped connections between cold-formed steel Z sections after careful calibration against test obtained from a total of 26 one point-load tests on lapped connections. Once the co-existing moments and shear forces in the lapped connections were evaluated, the critical sections were readily checked against combined bending and shear using codified design rules. Moreover, design expressions were also proposed for the evaluation of effective flexural rigidities of lapped connections with various bolt configurations against practical lap length to section depth ratios. Consequently, the structural behavior of lapped sections between cold-formed steel Z section in terms of strength and stiffness is quantified rationally for general design. Fiorino et al. (2007) tested screw connections between wood- or gypsum-based panels and cold-formed steel stud profiles. The main objectives of the study were: to compare the response of different types of panels, to study the effect of sheathing orientation, to examine the effect of the loaded edge distance, to examine the effect of different cyclic loading protocols, and to assess the effect of the loading rate. The outcomes of this experimental investigation were deeply discussed, aiming to select the main parameters affecting the shear behaviour of this type of connections. In addition, a procedure for the prediction of the lateral load displacement response of steel frame panel systems based on the obtained results was presented. Dubina and Zaharia (1997) presented an experimental research program aiming to evaluate the semi-rigid behaviour of some typical bolted connections used in cold formed steel plane truss joints. Structural performance of the connections was evaluated in term of strength and stiffness. A numerical analysis of this type of truss, in which this semi-rigid behaviour was taken into account using experimental results, was performed in order to demonstrate the improvement of load capacity in comparison with the classical assumptions. Chung and Lau (1999) presented an experimental investigation on the structural performance of cold formed steel members with bolted moment connections. Two lipped C sections back-to-back with interconnections are used as beam and column members. The structural performance and modes of failure of all tests were investigated. Among sixteen component and system tests, the moment resistance of bolted moment 627

8 connections with four bolts per member was found to lie between 42% and 84% of the moment capacities of the connected members. The beam column connections with haunched gusset plates failed at a much higher applied moment when compared with the other connection configurations. Thus, it was demonstrated that moment connections among cold formed steel members are structurally feasible and economical through rational design. Wong and Chung (2002) presented an experimental investigation on bolted moment connections between cold-formed steel sections. A total of 20 column base connection tests and beam-column sub frame tests with different connection configurations were carried out to assess the strength and stiffness of bolted moment connections between cold-formed steel sections. The beam and column members were double channel section Grade 450 N/mm 2 back to back. Findings showed that there was little difference in the moment resistances of connections with different bolt pitches while thicker gusset plates always give higher moment resistances. The presence of 50 mm deep chamfers was found to be effective in gusset plates 10 mm thick as their structural behaviour is similar to those gusset plates 16 mm thick but without chamfers. The moment resistance ratios of the connections were found to be over 90% with flexural failure in connected cold formed steel sections. Consequently, it was demonstrated that through rational design and construction, effective moment connections between coldformed steel sections might be readily achieved. Engineers are encouraged to build lightweight low to medium rise moment frames with cold-formed steel sections. Lim and Nethercot (2003) studied the behaviour and design of bolted momentconnections between cold-formed steel members, formed by using brackets bolted to the webs of the section. A combination of laboratory tests and finite element analysis were used in their investigation. It was demonstrated that there was a good agreement between the measured ultimate moment-capacity and the predicted value by using the finite element method. A parametric study conducted using the finite element model showed that the moment-capacity of a practical size joint can be up to 20% lower than that of the cold-formed steel sections being connected. Web buckling so-caused must therefore be considered in the design of such connections. The study done by Wong and Chung (2002) was later analyzed by Yu et al. (2005) to predict the structural behaviour of bolted moment connections between cold-formed steel sections. A non-linear finite element model of the beam column sub-frames incorporating the effect of semi-rigid joints was presented. On the basis of the measured moment joint rotation curves of the bolted moment connections, the overall lateral load deflection curves of the sub-frames were predicted, and they were found to follow closely the curves obtained from tests. The research proposed a semi-empirical formula for flexibility prediction and design rules for the proposed bolted moment connection. Chung et al. (2005) tested four column bases with different connection configurations, to investigate their moment resistance and typical modes of failure. A finite element model was generated using the ABAQUS (Version 6.4, 2004) software package was later established using shell and spring elements to model the sections and bolted fastenings respectively. Comparison between the test and numerical results was presented. Grade 450 cold-formed double channel steel sections of size of 150 mm depth and 64 mm width were used. The thicknesses of the sections were 1.6 mm and 2.0 mm respectively. All bolts used were 16 mm diameter of Grade 8.8. Column bases were formed with hotrolled steel plates 16 mm and 20 mm thick, into a T-shape, with the bolt pitch 180 mm and 240 mm. Findings showed that the proposed design and analysis method was 628

9 structurally adequate to predict the failure loads of column-base under shear and bending. Dundu and Kemp (2006) presented tests to determine the failure modes of the eaves region of steel portal frames. This was part of a major research project to establish the over all behaviour of steel portal frames, constructed from single channels and bolted back-to-back at the eaves joint. Variables in the 4 tests include the number of bolts in the connection, the points of contraflecture, the width of the channel flanges and the strength of the channels. Three modes of failure were observed. The final failure mode in all structures was local buckling of the compression flange and web. Local buckling was made more critical by stress concentrations, shear lag and bearing deformations caused by back-to-back connections. It proposed that a factor of 0.8 should be applied to the yield moment and the buckling moment of resistance to account for stress concentrations, shear lag and bearing deformations. Tan (2009) carried out research in Universiti Teknoloji Malaysia to develop the design procedures of bolted beam to column connections for double channel cold-formed steel sections, to study the pin and partial strength behaviour of the developed connections based on their strength and stiffness performance, and to validate the performance of the proposed connection configurations by comparing the analytical calculation to experimental results. A series of full scale experimental investigation comprising of twenty-four isolated joint tests and twelve subassemblage frame tests were carried out to understand the connections strength and stiffness behaviour. The experimental results showed good agreement compared to theoretical predictions. From the experimental and analytical results, some of the connections were classified as pin joints, with the strengths less than 25% of beam capacity; while others were classified as partial strength joints with moment resistance of joints were in the range of 46% to 96% to the moment resistance of the connected beam. Uang et al. (2010) carried out cyclic tests on nine full-scale beam-column sub assemblages. With double channel beams and HSS columns interconnected by bearingtype high-strength bolts, all specimens showed a story drift capacity significantly larger than 0.04 radian. Typical response is characterized by a linear response, a slip range, followed by a significant hardening region due to bolt bearing. Three failure modes were identified. Confining in the connection region, inelastic action through bolt slippage and bearing was ductile and desirable. Such inelastic action always occurs first, but either column or beam may also experience buckling. Beam buckling was most undesirable due to significant post-buckling strength degradation. Extending the concept of instantaneous centre of rotation of an eccentrically loaded bolt group, a model that can reliably simulate the cyclic behaviour of the bolted moment connection was presented. A few research works have been done on cold formed steel frames. Tan (2001) presented the analysis and tests of cold-formed thin-walled channel frames including nonlinear flexible or semi-rigid connection behaviour. The semi-rigid connection behaviour was modelled using a mathematical approximation of the connection flexibility or momentrotation relationship. Local instability in the form of local buckling of members was included in the analysis. The full response of the frame, up to the collapse load, can be predicted. Experimental investigation was carried out on a series of simple double storey symmetrical frames with the purpose of verifying the accuracy and validity of the analysis. Agreement between the theoretical and experimental results was acceptable. The investigation also showed that affect of connection thickness on the strength of thinwalled frames is less significant compared to that of the member s thickness and lip size. Lim and Nethercot (2004) presented a linear finite element model of cold-formed steel portal frame for comparison with experimental results. Two approaches were adopted for 629

10 the analysis; a full three dimensional linear shell element using ABAQUS software and a linear beam elements with ANSYS program were used to idealize the column and rafter members, and rotational spring elements are used to represent the rotational flexibility of the joints. In addition, the beam idealization took into account the finite connection length of the joints. Deflections predicted using the beam idealization was shown to be comparable to deflections obtained from both a linear finite element shell idealization and full-scale laboratory tests. Deflection predicted using the beam elements are shown to be close to those predicted using more accurate shell model. Therefore, using the beam idealization, engineers can analyze and design cold-formed steel portal frames, including making appropriate allowances for connection effects, without the need to resort to expensive finite element shell analysis. Kwon et al. (2006) investigated the performance of the connections constituting a pitched roof portal frame by holding a series of connection tests which were composed of closed cold-formed steel sections. The flexural strength of the section was investigated first and the structural behaviour of the connections including the moment-rotation relation, the yield, and ultimate moment capacity of the connections were studied experimentally. The connection test specimens consisted of column base, eave, and apex connections of the portal frame. The main factors of the connection test were the thickness and the shape of the mild steel connection element. Finally, the portal frame was tested under both constant vertical and increasing horizontal loads to failure. The pitched roof portal frame test showed that the semi rigid connections developed had high structural performance and could successfully be applied to portal frames. A numerical model of the portal frame using LUSAS (2002) for comparison with the test results was presented. A simplified model with the beam and joint elements that could consider an overall joint characteristic explicitly was adopted for the analysis. Since the numerical analysis of the frame could not include the material inelasticity and fracture of clinching of connections, the load calculated was much higher than test results after the displacement was increased beyond twice the allowable limit. Raftoyiannis I.G (2005) prepared a linear stability analysis for establishing the combined effect of joint flexibility and an elastic bracing system on the buckling load of steel plane frames. Based on the beam-to-column model of Eurocode 3, the subsequent study showed that joint flexibility is a very important parameter that needs to be incorporated into the stability analysis of frames with semi rigid connections. It was found that assuming flexible connections in such frames always leads to a reduction of their buckling load, which is proven to be significant in many characteristic cases. Numerical results for simple elastically braced or unbraced frames with semi-rigid connections, in tabular and graphical form, reveal the pronounced effect of joint flexibility and elastic bracing on their buckling load. Dawe and Wood (2006) tested twenty three small-scale roof trusses fabricated from coldformed steel to ultimate capacity. Each specimen was subjected to a single point load at the ridge. One series of specimens was fabricated with a hinge connection at the ridge while a second series had a gusset plate connection at this location. The hinge served to isolate the strength properties of the heel connection and upper chords while the addition of the ridge plate provided information that could be used to quantify the load sharing between the ridge and heel connections. The performance of several heel plate configurations, altered by adding edge stiffeners and varying their shapes and thicknesses, 630

11 was evaluated. Local buckling of the top chord adjacent to the heel plate was the predominant failure mechanism in combination with distortion of the heel plates in instances where the plates were inadequately stiffened. Methods of reinforcing the top chords to prevent local buckling were investigated. Research on joints and structures among cold formed steel members as reviews mentioned by the authors involved the application of cold formed steel in wider area and high strength steel. It was found (from the review) that bolted moment connection among single cold-formed steel frames is a new research area. In addition, the employment of simple and effective joint can assist development of cold-formed steel structure in building construction. Review also showed that limited research was exposed on the numerical analysis in cold-formed steel structures as mentioned by McDonald et al. (2008). Ideas of testing bolted moment connections (between single cold-formed steel channel sections) of cold formed steel frame are stimulated from gap of the review; they are proposed to be studied in detail by both experimental and numerical approach. 5. Conclusions The structural use of cold formed steel in construction continually growing rapidly across the world exceeded that for hot rolled steel structural members. The use of thinner sections and high strength steels leads to design problems for structural engineers, which may not normally be encountered in routine structural steel design. This paper has concentrated on structural design consideration of cold formed steel sections and research developments on joints and structures, which have come into view in the principal journals in this area in purpose of increasing the usage of cold formed steel members. It was concluded (from the review) that studying connections and portal frame among single cold formed steel sections in both experimental and numerical approach becomes a new area of study. 6. References 1. ABAQUS (2004), User s Manual: Version 6.4 Hibbitt- Kaloss and Sorensen. Inc. 2. American Iron and Steel Institute (1996), AISI Specification for the design of cold-formed steel structural members. Washington (DC). 3. American Iron and Steel Institute (2004), Commentary on Appendix 1 Design of Cold-Formed Steel Structure Members with the Direct Strength Method. 4. ANSYS (1994), User Manual of for Revision 5.3-Procedures Vol. I. USA: Swanson Analysis Systems. 5. British Standards Institution (1998), BS5950: Structural use of steelwork in buildings: Part 5: Code of practice for the design of cold-formed sections. London. 6. British Standards Institution (2006), Eurocode 3: Design of steel structures- Part 1.3: General rules- Supplementary rules for cold-formed thin gauge members and sheeting. London. BS EN

12 7. Chen J. and Young B. (2006), Corner properties of cold-formed steel sections at elevated temperatures. Thin-Walled Structure, 44, pp Chung K.F. and Ip K.H. (2001), Finite element investigation on the structural behavior of cold formed steel bolted connections. Engineering structure, 23, pp Chung K.F., Ho H. C. (2005), Analysis and design of lapped connections between cold-formed steel Z sections. Thin-Walled Structures, 43, pp Chung K.F., Lau L. (1999). Experimental investigation on bolted moment connections among cold formed steel members. Engineering Structure, 21, pp Chung K.F., Lawson R.M. (2000), Structural performance of shear resisting connections between cold-formed steel sections using web cleats of cold-formed steel strip. Engineering Structures, 22, pp Chung, K.F. (1993), Building design using cold-formed steel sections: Worked examples to BS5950: Part 5: 1987, The Steel Construction Institute. 13. Chung, K.F.,Yu, W.K. and Wang A.J. (2005), Structural performance of coldformed steel column bases with bolted moment connections. Steel and Composite Structures, 5(4), pp Dawe J. L. and Wood J. V. (2006), Small-scale test behavior of roof trusses cold-formed steel. ASCE, 132(4), pp Dubina D. (2008), Behavior and performance of cold-formed steel-framed houses under seismic action. Journal of Constructional Steel Research, 64, pp Dundu M., Kemp A. R. (2006), Strength requirements of single cold-formed channels connected back-to-back. Journal of Construction Steel Research, 62, pp Fan L, Rondal J, Cescotto S. (1997), Finite element modelling of single lap screw connections in steel sheeting under static shear. Thin-Walled Structures, 27(2), pp Fiorino L., Corte G. D., and Landolfo R. (2007), Experimental tests on typical screw connections for cold-formed steel housing. Engineering Structures, 29, pp Hancock, G.J. (1998), Design of Cold-Formed Steel Structures. 3rd edition. 632

13 20. Hancock, G.J. (2003), Review Article: Cold-formed steel structures. Journal of Constructional Steel Research, 59, pp Kwon Y. B.; Chung H. S.; and Kim G. D. (2006), Experiments of cold-formed steel connections and portal frames. ASCE, 132(4), pp LaBoube R. A., Soko M. A. (2002), Behavior of screw connections in residential construction. ASCE, 128(1), pp Lawson, R.M., Chung, K.F. and Popo-Ola, S.O. (2002), Building Design using Cold-formed Steel Sections, Structural Design to BS5950-5: Section properties and load tables. The Steel Construction Institute. SCI-P276, Lim J. B. P., Nethercot D.A. (2004), Finite element idealization of a cold-formed steel portal frame. ASCE, 130(1), pp Lusas element reference manual & user s manual (Ver. 13.4). (2002). FEA Co. Ltd. :Surrey: U.K. 26. McDonald, M., Heiyantuduwa, M.A., Rhodes, J. (2008). Recent developments in the design of cold-formed steel members and structures. Thin-Walled Structures, 46, pp Raftoyiannis I.G (2005), The effect of semi-rigid joints and an elastic bracing system on the buckling load of simple rectangular steel frames. Journal of Constructional Steel Research, 61, pp Rhodes, J. and Shanmugam N.E. (2003), Cold-formed Steel Structures. In: Chen, W.F. and Richard Liew, J.Y. The Civil Engineering Handbook. 2nd Edition. US: CRC Press LLC. 29. Rondal J. (2000), Cold formed steel members and structures-general report. Journal of Construction Steel Research, 55, pp Tan S.H. (2001), Channel frames with semi-rigid joints. Computers and Structures, 79, pp Uang, C., Sato A., Hong J., and Wood K. (2010), Cyclic testing and modeling of cold-formed steel: special bolted moment frame connections. ASCE, 136(8), pp Wang M.F., Chung K.F. (2002), Structural behavior of bolted moment connections in cold-formed steel beam-column sub-frames. Journal of Constructional Steel Research, 58, pp Young B, Hancock GJ. (2001). Design of cold-formed channels subjected to web crippling. Journal of Structural Engineering, 127(10), pp

14 34. Yu, W.K., Chung, K.F., Wong, M.F. (2005), Analysis of bolted moment connections in cold- formed steel beam-column sub frames. Journal of Constructional Steel Research, 61, pp Yu, W.W. (2000), Cold-Formed Steel Design. 3rd edition. John Wiley and Sons Inc. 634