Cold-formed Steel Channel Sections Research Articles

An analytical solution of distortional buckling resistance of cold-formed steel channel-section beams with web openings

Circular holes can be commonly found in the web of cold-formed steel beams to accommodate services such as electric wires and pipelines. The presence of holes will reduce the critical buckling stress of the beams. Hancock proposed solution for determining the distortional critical stress of channel section beams, but limited to the sections without holes. This paper presents an analytical study on the distortional buckling of cold-formed steel channel-section beams with circular holes in the web. Hancock's solution has been modified to derive a simple formulation for approximating the elastic critical stress and moment of distortional buckling of the channel-section beams with circular holes in the web, which are compared with those from the finite element buckling analysis using ANSYS. Finally, the influence of multiple holes on the distortional buckling behaviour and corresponding elastic buckling stress of beams in bending is discussed.

Mechanical Behaviour for Connection of Cold-Formed Steel Channel Section with Intermediate Web Stiffener

Cold-formed steel (CFS) is a popular steel-based material for building such as roof truss system and wall frame panel. CFS with a variety of shapes, cross-sections and thickness produce a lot of advantages such as ease of production, corrosion resistance and high strength to weight ratio. Connection of the CFS sections between them uses screw, bolt and nut, rivet or weld. But, the detail information for the connector in standard either by Eurocode 3 or American Iron and Steel Institute (AISI) is still incomplete especially methods for testing and also lack in the basic knowledge of testing for the connector or combination of connectors. The connector that was used in this study was a self-drilling screw. The objective of the study is to provide the mechanical behaviour information of self-drilling screws from shear and pull-out tests. Both tests utilised Universal Testing Machine with 100 kN capacity to determine the ultimate load and load-deformation behaviour of the self-drilling screws with different numbers. As a result, the ultimate load of the specimen was found to increase with increasing number of the self-drilling screws for shear and pull-out connection tests.

Experimental and numerical investigation into the behaviour of face-to-face built-up cold-formed steel channel sections under compression

Face-to-face built-up cold-formed steel channel sections are becoming increasingly popular for column members in cold-formed steel structures; its applications include cold-formed steel trusses, space frames and portal frames. In such an arrangement, the independent buckling of the members is resisted by intermediate fasteners. In the literature, no research is available for such face-to-face built-up cold-formed steel columns. The issue is addressed herein. This paper presents the results of 36 experimental tests, conducted on face-to-face built-up cold-formed steel channel-sections covering a wide range of slenderness from stub to slender columns. A nonlinear finite element model is then described that shows good agreement with the experimental results. The finite element model includes material non-linearity, initial imperfections and modelling of intermediate fasteners. Both finite element and experimental results are compared against the design strengths calculated in accordance with the American Iron and Steel Institute (AISI), Australian and New Zealand Standards (AS/NZS) and Eurocode (EN 1993-1-3). The verified finite element model is used for the purposes of a parametric study comprising 90 models. The effect of fastener spacing on the axial strength was investigated. From the results of experiments and finite element investigations, it is shown that the design in accordance with the AISI & AS/NZS and Eurocode (EN 1993-1-3) is generally conservative by around 15%, however, AISI & AS/NZS and Eurocode (EN 1993-1-3) can be un-conservative by 8% on average for face-to-face built-up columns failed through local buckling.

Effect of thickness on the behaviour of axially loaded back-to-back cold-formed steel built-up channel sections - Experimental and numerical investigation

In cold-formed steel structures, such as trusses, wall frames and portal frames, the use of back-to-back built-up cold-formed steel channel sections are becoming increasingly popular. In such an arrangement, intermediate fasteners are required at discrete points along the length, preventing the channel-sections from buckling independently. Current guidance in the AISI &AS/NZS for such back-to-back built-up cold-formed steel channel sections requires the use of modified slenderness in order to take into account the spacing of the fasteners. Limited research has been done on back-to-back built-up cold-formed steel columns to understand the effect of column thickness and slenderness's on axial capacity. This issue is addressed herein. This paper presents the results of 60 experimental tests performed on back-to-back built-up cold-formed steel channel sections under compression. Detailed observations on different failure modes and column strengths were made through varying thickness, length and cross section of columns. A non-linear finite element model was developed which includes material non-linearity, geometric imperfections and explicit modelling of web fasteners. The finite element model was validated against experimental results. A comprehensive parametric study consisting of 204 models has been carried out covering a wide range of thickness and slenderness for the considered back-to-back built-up columns. Axial capacities obtained from the numerical study were used to assess the performance of the current AISI& AS/NZS standards when applied to cold-formed back-to-back built up columns; obtained comparisons showed that AISI& AS/NZS standards are un-conservative for stub and short columns which were failed by local buckling whereas standards were over-conservative for the strength of intermediate and slender columns which were failed mainly by overall member buckling. This paper has therefore proposed improved design rules and verified their accuracy using finite element analysis and test results of back-to-back built-up cold-formed channel sections, subjected to axial compression.

Nonlinear behaviour of back-to-back gapped built-up cold-formed steel channel sections under compression

In cold-formed steel structures, such as trusses and portal frames, the use of back-to-back gapped built-up cold-formed steel channel-sections for column members are becoming increasingly popular. In such an arrangement, the lowest flexural buckling mode may not necessarily be overall buckling of the whole column. In the literature, only three test results have been previously reported for such cold-formed steel columns, and limited to values of non-dimensional slenderness ranging from 1.08 to 1.16. This issue is considered herein. The results of 40 experimental tests are reported, conducted on back-to-back gapped built-up cold-formed steel channel-sections covering the range of non-dimensional slenderness from stub to slender columns. A nonlinear finite element model is then described that shows good agreement with the experimental results. The finite element model is then used for the purposes of a study comprising 84 models. Using the experimental and finite element results, it is shown that design in accordance with the American Iron and Steel Institute (AISI) and Australian and New Zealand Standards (AS/NZS) can be conservative by as much as 53%. However, use of a modification to the non-dimensional slenderness, that considers the gap, results in the design standards being within 5% conservative with respect to the experimental and finite element results.

Geometric Imperfection Measurements and Validations on Cold-Formed Steel Channels Using 3D Noncontact Laser Scanner

A three-dimensional (3D) noncontact laser-scanning method to quantify the deviations in cold-formed steel (CFS) channel sections (plain and lipped) is presented. The methodologies to segregate the different categories of imperfections from the deviations in the geometry of CFS member are also presented. A total of 24 different C-sections (minimum of six samples in each section) with varying cross-sectional parameters totaling 188 specimens were studied. The nature of imperfections in the CFS members was found to correlate with geometric properties such as slenderness ratios, torsional constant, and plate slenderness. The bow and camber imperfection (global out-of-straightness) in the members is presented with respect to the minor and major axis slenderness ratios. A new combined global and cross-sectional parameter (J/L) is introduced against the deviation caused by twisting of the CFS member. To predict the imperfection magnitudes based on their geometrical properties, a new set of expressions are suggested.

A simplified flange–lip model for distortional buckling of cold-formed steel channel-sections with stiffened web

This paper presents a simplified analytical model for determining the critical stress of distortional buckling of lipped channel-sections with stiffened web made from cold-form steel (CFS). Lipped channel-section with stiffened web have been shown to have a distinct advantage in resisting local buckling and are associated with the higher distortional buckling stress, when compared to the channel-section without stiffeners. It is widely used as a substitution for standard channel-section in cold form steel construction applications. In the current work, CFS channel-sections with stiffened web are investigated based on the flange–lip model. In order to determine the stiffness of rotational springs representing the restraining effect of the web to the flange–lip system, the web with different type of stiffeners is modeled as an orthopedic plate. Using the total potential energy principle, the formula for calculating the local buckling stress of the stiffened web considering loading scenarios including a pure compression and a pure bending moment are derived. The stiffness of rotational spring can be obtained. Finally, the prediction of distortional buckling critical stress of lipped channel-section with different type of stiffened webs is carried out, which is shown to be in good agreement with those calculated by the finite strip method (FSM).

Design Optimization of Long-Span Cold-Formed Steel Portal Frames Accounting for Effect of Knee Brace Joint Configuration

The application of cold-formed steel channel sections for portal frames becomes more popular for industrial and residential purposes. Experimental tests showed that such structures with long-span up to 20 m can be achieved when knee brace joints are included. In this paper, the influence of knee brace configuration on the optimum design of long-span cold-formed steel portal frames is investigated. The cold-formed steel portal frames are designed using Eurocode 3 under ultimate limit states. A novel method in handling design constraints integrated with genetic algorithm is proposed for searching the optimum design of cold-formed steel portal frames. The result showed that the proposed routine for design optimization effectively searched the near global optimum solution with the computational time is approximate 50% faster than methods being popularly used in literature. The optimum configuration for knee brace joint can reduce the section size of rafter and so the lighter frame could be obtained especially for long-span portal frame. The minimum weight of main frame obtained from optimization process is approximate 19.72% lighter than a Benchmark Frame used in the full-scale experimental test.

Experimental Study of Axially Tension Cold Formed Steel Channel Members

Experimental testing is commonly used as one of the steps to determine the cause of the collapse of a building structure. The collapse of structures can be due to low quality materials. Although material samples have passed laboratory tests and the existing technical specifications have been met but there may be undetected defects and known material after failure. In this paper will be presented Experimental Testing of Axially Tension Cold Formed Steel Channel Members to determine the cause of the collapse of a building roof truss x in Pekanbaru. Test of tensile strength material cold formed channel sections was performed to obtain the main characteristics of Cold Formed steel material, namely ultimate tensile strength loads that can be held by members and the yield stress possessed by channel sections used in construction. Analysis of axially tension cold formed steel channel section presents in this paper was conducted through experimental study based on specificationsAnnualBook of ASTM Standards: Metal Test methods and Analitical Procedures, Section 3 (1991). The result of capacity loads experimental test was compared with design based on SNI 03-7971-2013standard of Indonesia for the design of cold formed steel structural members. The results of the yield stress of the material will be seen against the minimum allowable allowable stress range. After the test, the percentace of ultimate axial tension capacity theory has a result that is 16.46% larger than the ultimate axial tension capacity experimental. When compared with the load that must be borne 5.673 kN/m it can be concluded that 2 specimens do not meet. Yield stress of member has fulfilled requirement that wass bigger than 550 MPa. Based on the curve obtained ultimate axial tension capacity theory, results greater than experimental. The greatest voltage value (fu) is achieved under the same conditions as its yield stress. For this specimen with a melting voltage value fy = 571.5068 MPa has fulfilled the minimum melting point value of 550 MPa required for standard mild steel materials in accordance with the code SNI 03-7971-2013 about Cold formed steel.

Experimental Study of Axially Tension Cold Formed Steel Channel Members

Experimental testing is commonly used as one of the steps to determine the cause of the collapse of a building structure. The collapse of structures can be due to low quality materials. Although material samples have passed laboratory tests and the existing technical specifications have been met but there may be undetected defects and known material after failure. In this paper will be presented Experimental Testing of Axially Tension Cold Formed Steel Channel Members to determine the cause of the collapse of a building roof truss x in Pekanbaru. Test of tensile strength material cold formed channel sections was performed to obtain the main characteristics of Cold Formed steel material, namely ultimate tensile strength loads that can be held by members and the yield stress possessed by channel sections used in construction. Analysis of axially tension cold formed steel channel section presents in this paper was conducted through experimental study based on specificationsAnnualBook of ASTM Standards: Metal Test methods and Analitical Procedures, Section 3 (1991). The result of capacity loads experimental test was compared with design based on SNI 03-7971- 2013standard of Indonesia for the design of cold formed steel structural members. The results of the yield stress of the material will be seen against the minimum allowable allowable stress range. After the test, the percentace of ultimate axial tension capacity theory has a result that is 16.46% larger than the ultimate axial tension capacity experimental. When compared with the load that must be borne 5.673 kN/m it can be concluded that 2 specimens do not meet. Yield stress of member has fulfilled requirement that wass bigger than 550 MPa. Based on the curve obtained ultimate axial tension capacity theory, results greater than experimental. The greatest voltage value (fu) is achieved under the same conditions as its yield stress. For this specimen with a melting voltage value fy = 571.5068 MPa has fulfilled the minimum melting point value of 550 MPa required for standard mild steel materials in accordance with the code SNI 03- 7971-2013 about Cold formed steel.

Web crippling studies of SupaCee sections under two flange load cases

Cold-formed steel channel sections are generally used as flexural members in light weight steel construction. Improved channel section profiles such as SupaCee sections with longitudinal web stiffeners and curved lips are also used instead of the conventional lipped channel sections. Web crippling capacities of these innovative sections can be different from those of conventional lipped channel sections. However, the web crippling behaviour and strength of these high strength SupaCee sections has not been investigated yet. Current web crippling design methods given in cold-formed steel design standards do not include any design procedures for SupaCee sections. Hence an experimental study involving 36 web crippling tests was first undertaken to investigate the web crippling behaviour and strengths of SupaCee sections under two flange load cases with their flanges unfastened to the supports. Comparison of experimental results showed that the web crippling capacities of SupaCee sections are reduced in comparison to lipped channel sections. Therefore the current web crippling design equations in the American and Australian/New Zealand cold-formed steel design standards were modified by including suitable web crippling coefficients for SupeCee sections. Finite element models of tested SupaCee sections were also developed and validated using the experimental results. This paper presents the details of the experimental and numerical web crippling studies of SupaCee sections under two flange load cases and the results. It also presents the details of direct strength method based design equations developed in this research.

Recent Contributions to the Analysis and Design of Cold Formed Steel Channels

Background: Cold formed steel channels are widely used in building construction. Advances in material technology contributed to the production of very thin cold formed steel channel sections with high yield strength that can be utilized in the industry in order to achieve light weight design. Extensive research work was conducted in the past three decades to explore the behavior of channel members used in various engineering applications and improve the design procedures. Objectives: The paper presents a comprehensive review of recent contributions and patents for the analysis and design of thin walled steel channel members. Method: The paper reviews engineering work developed in the past three decades to detail the behavior of channel members under various types of loadings. North American and European design code provisions are discussed. Empirical and simplified analytical models that were developed to estimate the channel ultimate strength for various limit states are also described. Results: Design investigations for local/distortional buckling effective width, influence of perforations, splice connections, fire performance, optimization, composite channel sections and defective channels are discussed. Conclusion: A state of the art “reference-manual” is presented for the analysis and design of cold formed steel channels that can be effectively utilized by practicing Engineers for various industrial applications. Keywords: Cold formed steel channels, finite element, steel design, plates, residual stress, fatigue cracks, imperfections, corrosion, fire performance, composite channels, stiffened plates.

Experimental Investigation of Tensile Test on Connection of Cold-formed Cut-curved Steel Section

Cold-formed steel (CFS) is widely used as structural and non-structural components such as roof trusses and purlin. A CFS channel section with double intermediate web stiffener and lipped is chosen based on the broader usage in roof truss construction. CFS section is cut to form cold-formed pre-cut-curved steel section and lastly strengthened by several types of method or likely known as connection to establish the cold-formed cut-curved steel (CFCCS) section. CFCCS is proposed to be used as a top chord section in the roof truss system. The CFCCS is to resist the buckling phenomena of the roof truss structure and reduced the compression effect on the top chord. The tensile test connection of CFCCS section, especially at the flange element with eight types of connection by welding, plate with self-drilling screw and combination is investigated. The flange element is the weakest part that must be solved first other than the web element because they are being cut totally, 100% of their length for curving process. The testing is done using a universal testing machine for a tensile load. From the experiment, specimen with full welding has shown as a good result with an ultimate load of 13.37 kN and reported having 35.41% when compared with normal specimen without any of connection methods. Furthermore, the experimental result is distinguished by using Eurocode 3. The failure of a full welding specimen is due to breaking at the welding location. Additionally, all specimens with either full weld or spot weld or combination failed due to breaking on weld connection, but specimen with flange plate and self-drilling screw failed due to tilting and bearing. Finally, the full welding specimen is chosen as a good connection to perform the strengthening method of CFCCS section.

Tension Behaviour on the Connection of the Cold-Formed Cut-Curved Steel Channel Section

Cold-formed steel (CFS) are utilised as a non-structural and structural element in construction activity especially a residential house and small building roof truss system. CFS with a lot of advantages and some of disadvantages such as buckling that must be prevented for roof truss production are being studied equally. CFS was used as a top chord of the roof truss system which normally a slender section is dramatically influenced to buckling failure and instability of the structure. So, the curved section is produced for a top chord for solving the compression member of the roof truss. Besides, there are lacked of design and production information about the CFS curved channel section. In the study, the CFS is bent by using a cut-curved method because of ease of production, without the use of skilled labour and high cost machine. The tension behaviour of the strengthening method of cut-curved or could be recognised as a connection of the cut-curved section was tested and analysed. There are seven types of connection was selected. From the testing and observation, it is shown the specimen with full weld along the cut section and adds with flange element plate with two self-drilling screws (F7A) was noted to have a higher value of ultimate load. Finally, there are three alternative methods of connection for CFS cut-curved that could be a reference for a contractor and further design.

Effect of screw spacing on behavior of axially loaded back-to-back cold-formed steel built-up channel sections

In cold-formed steel structures, such as trusses, wall frames, and portal frames, the use of back-to-back built-up cold-formed steel channel sections for the column members is becoming increasingly popular. In such an arrangement, intermediate fasteners at discrete points along the length prevent the individual channel sections from buckling independently. Current guidance by the American Iron and Steel Institute and the Australian and New Zealand Standards for built-up sections describes a modified slenderness approach, to take into account the spacing of the screws. Limited experimental tests or finite element analyses, however, have been reported in the literature for such sections to understand the effect of screw spacing. This issue is addressed herein. The results of 30 experimental tests are reported, conducted on back-to-back built-up cold-formed steel channel sections covering stub columns to slender columns. A finite element model is then described which shows good agreement with the experimental test results. The finite element model is then used for the purposes of a parametric study comprising 144 models. It is shown that while the modified slenderness approach is in general conservative, for stub columns it can be unconservative by around 10%.

Optimum design of cold-formed steel portal frame buildings including joint effects and secondary members

In steel portal frames, cold-formed steel channel sections are increasingly used as the primary framing components, in addition to the secondary members e.g. purlins and side rails. For such framing systems, the stiffness of the joints at the eaves and apex affects the bending moment distribution, as well as the frame deflections. This paper investigates the influence of two joint configurations having full rigidity and semi-rigidity, respectively, on the optimum design of cold-formed steel portal frames. A real-coded genetic algorithm is used to search for the most cost-effective design. It is shown that through incorporating joint effects explicitly into the design process, a more appropriate balance between the joints and the member properties can be obtained, thus optimizing material use. The study then investigates the effect of secondary members on the optimum design. It is shown that incorporating the secondary members is important for portal frames having spans shorter than 12 m. For example, for a frame spacing less than 6 m, the material cost of the primary members can be reduced by up to 15%.

Cost Effectiveness of CFRP Repair Technique for Cold Formed Steel Beams

Objectives: Structural steel can be broadly classified into hot rolled steel and cold formed steel (CFS). CFS manufactured from roll forming or press braking operation. The main advantage of CFS sections are thin wall and light weight. These thin wall leads to buckling of structural member. This paper aims to study the capacity of Carbon Fibre Reinforced Polymer (CFRP) strengthened CFS channel beams, buckling behaviour, deflection and cost studies on CFRP strengthening. Methods/Statistical analysis: In this study three different length of CFS channel sections are selected for testing in which beams are tested for bending. All the beams were tested in plain section and CFRP strengthened series in universal testing machine. Findings: Experimental results shows the enhancement in capacity of beam due to CFRP strengthening. The local and distortional buckling modes were observed as failure modes. Experimental results were compared with maximum load resistance calculated by AISI specification which are in good agreement. Cost studies were compared on replacing a new member with CFRP strengthened channel member. Improvements/Applications: CFRP strengthening is suitable for enhancement of capacity of beams and repair. This CFRP strengthening technique can applied to reinforced concrete members, hot rolled steel, in filled steel tubes and bridges etc.

Distortional buckling of perforated cold-formed steel channel-section beams with circular holes in web

This paper presents the numerical and analytical investigations on the distortional buckling of perforated cold-formed steel channel-section beams with circular holes in web. The numerical investigation involves the use of finite element methods. In the analytical analysis the distortional buckling model recommended in EN1993-1-3 is employed. The influence of the web holes on the distortional buckling behaviour and corresponding critical stress and moment of perforated cold-formed steel channel-section beams are discussed. Finally, a simple analytical formulation is proposed for evaluating the effect of hole size on the reduction of critical stress and critical moment of the channel-section beams with circular holes in web.

Effects of edge-stiffened circular holes on the web crippling strength of cold-formed steel channel sections under one-flange loading conditions

Cold-formed steel sections are often used as wall studs or floor joists and such sections often include web holes for ease of installation of services. The holes are normally punched or bored and are unstiffened; when the holes are near to points of concentrated load, web crippling can be the critical design consideration. Recently, a new generation of cold-formed steel channel sections with edge-stiffened circular holes has been developed, for which web crippling may not be so critical. In this paper, a combination of experimental investigation and non-linear elasto-plastic finite element analyses are used to investigate the effect of such edge-stiffened holes under the interior-one-flange (IOF) and end-one-flange (EOF) loading conditions; for comparison, sections without holes and with unstiffened holes are also considered. A total of 90 results comprising 36 tests and 54 finite element analysis results are presented. Owing to manufacturing constraints, in the test programme, the edge-stiffener length was fixed at 13mm. Good agreement between the experimental and finite element results was obtained. For the case of the unstiffened hole, it is shown that the web crippling strength is reduced by up to 12% and 28% for the IOF and EOF loading conditions, respectively. However, with the edge-stiffened circular hole, the web crippling strength is only reduced by 3% for the IOF loading condition and there is no reduction in strength for the EOF loading condition. The finite element model was used for the purposes of a parametric study on the effects of different hole sizes, edge-stiffener length and distances of the web holes to the near edge of the bearing plate. The results indicate that with a suitable edge-stiffener length, the web crippling strength of cold-formed steel channel section with holes can be as high as the one without holes.

Web crippling behaviour of cold-formed steel channel sections with web holes subjected to interior-one-flange loading condition – Part II: parametric study and proposed design equations

A parametric study of cold-formed steel sections with web openings subjected to web crippling under interior-one-flange (IOF) loading condition is undertaken, using finite element analysis, to investigate the effects of web holes and cross-sections sizes. The holes are located either centred beneath the bearing plate or with a horizontal clear distance to the near edge of the bearing plate. It was demonstrated that the main factors influencing the web crippling strength are the ratio of the hole depth to the depth of the web, the ratio of the length of bearing plate to the flat depth of the web and the location of the holes as defined by the distance of the hole from the edge of the bearing plate divided by the flat depth of the web. In this study, design recommendations in the form of web crippling strength reduction factor equations are proposed, which are conservative when compare with both the experimental and finite element results.