Cold-formed Steel Structural Members Research Articles

Proposal for design rules of axially loaded CFRP strengthened cold formed lipped channel steel sections

Carbon fiber reinforced polymer (CFRP) composites are considered to have high performance and potential for use in strengthening , retrofitting and for the rehabilitation of structural sections. In this paper, design procedures are proposed for the axial load capacity of cold formed steel lipped channel columns strengthened with carbon fiber reinforced polymer (CFRP). For the purpose of validation, the results are based on the proposed design equation from the North American specification for the design of cold-formed steel structural members (AISI-2007) and Euro code for cold-formed members and sheeting (EC3-EN1993-1-3:2006) are compared against the experimental test data. The test results showed that the capacity of the columns are close to the theoretical values predicted by the AISI-2007 and EC 3 provisions. Some tested specimens showed reduced capacity and premature failure due to peeling and debonding of the CFRP from the steel. Various experimental investigations are suggested for future work to further validate and update the design equations. From the experimental studies, it has been observed that there is significant increase in strength due to CFRP strengthening.

Experimental Study of Axially Compressed Cold Formed Steel Channel Columns

Analysis and design of axially compressed cold formed steel channel section presented in this paper was conducted through experimental study, design based on British standards and North American Specification for the design of cold-formed steel structural members. More than 18 laboratory experiments were undertaken first on these steel channel columns under axial compression. A series of parametric studies were also carried out by varying the thickness and column length. All of these columns failed by local and distortional buckling. The test results were compared with American (AISI-2007) and British Standards (BS5950-Part5) for the design of cold-formed steel structural members. The details of these investigation and the outcomes are presented in this paper.

Investigation of cold-formed steel structural members with perforations of different arrangements subjected to compression loading

An investigation of cold-formed steel sections subjected to compression loading was undertaken using Finite Element Analysis to study the effects of perforation positions on the load capacity of column members of lipped channel cross-section. For this purpose, a finite element model was developed using ANSYS and its accuracy was verified using experimental and theoretical results. The study showed that the ultimate load of the lipped channels under compression varied greatly with the perforation position. Comparisons of the finite element results and the test results are also made with existing design specifications, and conclusions are drawn on the basis of the comparisons.

Ultimate capacity of battened columns composed of four equal slender angles

Cold-formed steel structural members play a great role in modern steel structures due to their high strength and light weight. The behavior and strength of battened column members composed of slender angle sections are mainly governed by local buckling of angle legs or torsional buckling of the angle between batten plates. Moreover, local buckling depends on the interaction between the width–thickness ratio of angle leg, overall slenderness ratio of angle between batten plates and overall slenderness of column. Theoretical study has been carried out by a nonlinear material and geometrical finite element model. Numerous cases of slender battened column sections having different width–thickness angle leg ratios, overall slenderness ratios between batten plates and overall slenderness ratios are chosen in this study. Complete ultimate strength curves are drawn and different failure modes are studied by taking different member lengths, which produce local or torsional buckling of single angles between batten plates or overall buckling of the member. Empirical equations for the effect of shear deformation factor and the ultimate axial load capacities of members formed of battened slender angle sections are proposed. Strengths of axially loaded battened members predicted using finite element as well as the proposed empirical equations is compared with the design strengths obtained using North American and European codes. It is concluded that the design strengths predicted by North American and European codes are generally conservative, and these design rules have been shown to be reliable using reliability analysis.

Simplified Method for Critical Elastic Distortional Buckling of Cold-Formed Steel C and Z Sections

The Direct Strength Method (DSM) is a recently adopted design approach by the North American Specifications for Cold-Formed Steel Structural Members (AISI S100) for calculating the nominal strength of cold-formed steel (CFS) sections. The critical elastic buckling load shall be obtained in order to employ the DSM in computing the nominal strength of CFS members. The AISI S100 provides simplified methods for determining the critical elastic distortional buckling load. However it is found that the AISI S100 simplified methods are over conservative for the industrial standard C and Z sections in the U.S. This paper presents revised simplified methods for calculating the critical elastic distortional buckling loads of typical CFS C and Z sections in bending and axial compression loading respectively. The new methods yield more accurate results but similar computation cost compared to the existing methods. The new methods can be added to the DSM methodologies for designing CFS members.

Simplified Method for Elastic Distortional Buckling Stress of Cold-Formed Thin-Wall Steel Members

For the distortional buckling of cold-formed thin-wall steel members, the Direct Strength Method (DSM) is a recently adopted design approach by foreign standard, and Chinese professional standard Technical specification for low-rise cold-formed thin-wall steel buildings present the calculation formulas based on the Effective Area Method (EAM) .The key of both methods is the elastic distortional buckling stress .At present, the calculation methods about it are over conservative .Compare the calculation results of method in AISI S100with the one calculated by software CUFSM ,for C and Z sections in bending and axial compression loading respectively in the North American Specifications for Cold-Formed Steel Structural Members (AISI S100). This paper presents revised simplified methods for calculating the elastic distortional buckling stress. The new methods yield more accurate results but similar computation cost compared to the existing methods.

Composed columns from cold-formed steel Z-profiles: Experiments and code-based predictions of the overall compression capacity

Built-up cold-formed steel members are tested in compression. The main objective behind the experiments is to determine the overall compression capacity of double-Z columns, which are often used in the Belgian engineering practice. Eight full-scale tests on 4.45m long columns are performed and out-of plane displacements and strains at six locations per member are recorded. The effect of initial imperfections is evaluated based on the measured longitudinal strains at mid-height. An attempt to relate the obtained ultimate capacity to prediction methods, based on the European standard for steel structures [1,2], is presented. The assumptions made in the analytical prediction and the gaps within the cited standard are explained and discussed. Certain aspects of the behaviour of such members cannot be represented in an Eurocode-base prediction, due to the restricted scope of [1,2]. A reference is made to North American Specification for the design of cold-formed steel structural members [3] as well, where a slightly better design methodology is available. Amendments to EN 1993-1-3:2006 are proposed and a design approach, based on the direct strength method is presented.

Shear Strength of a Cold-Formed Steel Sheet in Bolted Connections Using Oversized Holes

AbstractThe North American specifications for the design of cold-formed steel (CFS) structural members provides equations for determining the sheet shear strength in bolted connections when standard holes are used. In applications of oversized holes, the specification requires experimental analysis to be conducted to ensure satisfactory performance. A research project was recently completed at the University of North Texas to investigate the behavior and performance of CFS bolted connections using oversized holes. This paper presents the findings on the sheet shear strength for oversized hole applications. The studied parameters in this research included the following: sheet thickness from 0.762 to 2.997 mm; connection type of single shear and double shear with a single bolt; and bolt diameters of 6.4, 9.5, 12.7, and 15.9 mm. The experimental results indicate that the use of oversized holes without a washer did not significantly weaken the sheet shear strength. Recommendations are provided for predicting ...

Design rules for web crippling of CFRP strengthened aluminium rectangular hollow sections

Web crippling failure (web buckling and web yielding) is critical for thin-walled members when subjected to concentrated load. Carbon fibre reinforced polymer (CFRP) is attracting increasing research interest as a strengthening material for metallic structural members. Improved web crippling capacity of aluminium rectangular hollow sections has been achieved with CFRP being attached to the exterior and/or interior of the webs from a series of tests conducted by the authors. This paper focuses on developing design rules for predicting the nominal crippling strength of CFRP strengthened sharp-corner aluminium tubular sections: rectangular hollow section (RHS) and square hollow section (SHS), under end bearing load. The existing design rules for bare sections without CFRP strengthening are firstly reviewed and assessed, including design rules for both cold-formed steel structural members (Australian/New Zealand standard (AS 4100-1998) and North American Specification) and aluminium structures (Australian/New Zealand standard (AS 1664-1997) and American aluminium design manual). They are modified to take account of the improved capacity due to CFRP strengthening. The proposed design rules are calibrated against test results.

Optical Measuring Technique for the Investigation of Built-Up Cold-Formed Steel Structural Members

The construction industry uses cold-formed steel (CFS) sheets in the form of galvanised thin-walled profiles and corrugated sheets. In the past decade, CFS profiles have been competing with their hot-rolled counterparts as primary structural members of industrial halls, office buildings and residential housing of up to 3-4 storeys. The spans and column heights achieved with CFS profiles are ever larger. Due to the large slenderness of these members, adequate strength and stability are necessary, as well as reliability in design. Thin-walled members go through buckling during all stages of their working life. Local buckling appears at loads sometimes much lower than the design load. Distortional buckling seriously reduces the member resistance. It interacts with warping and lateral-torsional buckling, being significant for these asymmetric open sections. To restrict these effects, builders employ double sections - usually two standard cold-formed shapes bolted together to form a built-up section. These sections have the advantages of symmetry, higher stability and strength. The design of built-up members involves many uncertainties - although the European standard includes guidelines on the prediction of local, distortional and global buckling, the partial integrity and interaction between the parts of the composed members is still not studied. To study the actual behaviour, built-up members are tested in bending. An optical device for 3D motion analysis measures the displacement of points of interest on the specimen. Two interacting cameras use parallax to obtain the position of an arbitrary number of reflective markers glued to the specimen. The device tracks the movement of the markers in a 3D coordinate system without any contact with the specimen. Standard displacement transducers measure vertical displacements to validate the results. The paper gives an appraisal of the applicability of the method, a summary of the difficulties faced and the outcome of the test campaign.

Materials properties of thick-wall cold-rolled welded tube with a rectangular or square hollow section

In order to determine the behavior of thick-wall cold-rolled steel sections with square and rectangular hollow cross-section, experiments concerning materials properties of the flat coupons, corner coupons, parent plate coupons and stub columns were carried out. Effects of cold forming process on material properties were investigated. The stub column test strengths were compared with the compressive strengths determined by the Australian/New Zealand and Chinese standards for designing the cold-formed steel structural members respectively. It has been shown that both strengths predicted by the Australian/New Zealand standard using material properties obtained from the flat coupon tests and strengths forecasted by the Chinese standard based on the mean design yield stress of the full section are quite conservative. The mean design strength determined by the Australian/New Zealand standard using the average design yield stress of the full section is just identical to that predicted by the Chinese standard based on material properties obtained from the flat coupon tests. The latter two design processes are preferable to the present steel tubes because safety and economical efficiency are both attainable. Coarse grains and Widmanstätten microstructure formed in welded joints contribute to high strengths and low plasticity of the flat specimens with welding seams.

Load-Carrying Capacity Estimation Methods for Cold-Formed Steel Lipped Channel Member Using Effective Width Method

Distortional buckling may occur for Cold-formed thin-walled steel lipped channel member except local buckling and overall buckling. The buckling of flange and lip are the important factor for the occurrence the distortional buckling. The different design codes have different design method for calculating plate buckling coefficient of flange and lip using the effective width method. So the effective width method in different codes are introduced and the load-carrying capacities of 100 lipped channel section compressive members collected from reference are computed using ‘Cold-formed steel structures (AS/NZS 4600:2005)’, ‘Supplementary rules for cold-formed members and sheeting(EN1993-1-3:2006)’, ‘North American specification for the design of cold-formed steel Structural Members(AISI-S100:2007)’, ‘Specification for the design of cold-formed steel structural members (AISI:1996)’ and ‘Technical code of cold-formed thin-walled steel structures’(GB50018-2002). The calculated results show that ‘Technical code of cold-formed thin-walled steel structures (GB50018-2002)’ and ‘Supplementary rules for cold-formed members and sheeting (EN1993-1-3:2006)’ are conservative and ‘Cold-formed steel structures (AS/NZS 4600:2005)’, ‘North American specification for the design of cold-formed steel Structural Members (AISI-S100:2007)’ and ‘Specification for the design of cold-formed steel structural members (AISI:1996)’ are unsafe. The elastic buckling stress of different lipped channel sections are predicted by finite strip program (CUFSM) and get the suggested calculation formula of plate buckling coefficient of flange according to regression Analysis. The calculated results using suggested plate buckling coefficient of flange are agree to test results.

Shear capacity and tension capacity of arc-spot welds for multi-overlap deck panels

Arc-spot welds fabricated in multi-overlap configurations are found in roof deck construction when steel sheets are stacked at a sidelap or endlap. A welding technique that maximizes the quality of arc-spot welds fabricated through several layers of thick sheets is presented. Weld specimens were fabricated through 1, 2 or 4 layers of steel sheets with thicknesses ranging from 0.76 to 1.52 mm (22 to 16 gauge). The most important factors to control during the welding are the current (high intensity), the electrode type (E4311) and the welding technique. Various sheet steel/weld configurations found in roof deck construction were included. Adequate weld quality could be achieved in all cases except that welds were undersized when the ratio of the thickness of the underlying material to total sheet thickness was less than 0.7. A total of 72 tension tests and 107 shear tests were completed. Of those, 31 shear specimens were loaded with a reversed cyclic protocol to examine the behaviour of arc-spot welds subject to seismic loading. All other specimens were loaded under monotonically increasing displacement. The results were compared with the provisions of the CSA S136 North American Specification for the Design of Cold-Formed Steel Structural Members. The CSA S136 equations for shear and tension resistance of arc-spot welds are generally conservative, even for welds fabricated through multi-overlap configurations with total sheet steel thicknesses exceeding the 3.81 mm limit. Nonetheless, modifications to the equation for the effective diameter and to Equations E2.2.1.2-2, E2.2.2-1, and E2.2.2-2 are recommended.

Experimental Investigation of High Strength Cold-Formed C-Sections in Combined Bending and Shear

In roof systems, a high strength steel profiled sheeting fastened to high strength steel cold-formed purlins of a lipped C- or Z-section is commonly used throughout the world. The design of such systems is performed according to the provisions of the limit states Australia/New Zealand Standard for Cold-Formed Steel Structures in Australia and the North American Specification for the Design of Cold-Formed Steel Structural Members in the United States. In both standards, which include the newly developed direct strength method of design (DSM), the method presented is limited to pure compression and pure bending. The situations of pure shear and combined bending and shear as occurs in a continuous purlin system are not considered. In order to extend the DSM to purlin systems, three different test series on high strength cold-formed C-section purlins have been performed at the University of Sydney. The test series include predominantly shear, combined bending and shear, and bending only test series. Two different section depths and three different thicknesses of the lipped channel section were tested in this study. Further, tests with and without torsion/distortion restraint straps screwed on the top flanges adjacent to the loading points were also considered. This paper summarizes the test results and formulas developed from the effective width method and the DSM. Proposals for design are included in this paper. Comparisons with the Australian Steel Structures Standard are also included to take account of the tension field action.

Strength of Screw Connections in Cold-Formed Steel Construction

This paper presents a review of the design provisions for screw-fastened cold-formed steel connections in the United States, including criteria for testing and evaluating the strength of screw fasteners. In addition, the paper examines the relationship between the connected elements/components computed connection strength and the strength of the connector (screws). Fastener strength test data from three independent manufacturers is presented and it is shown that as the thickness or yield strength of the connected elements/components is increased, the ratio of the fastener strength to the bearing/tilting strength decreases to values less than one-half in some cases. Analysis of the test data showed that even when the 2001 North American Specification (NASPEC) for the Design of Cold-Formed Steel Structural Members statistical requirements for distribution of the test data are met, the computed safety and resistance factors can exceed the recommended limits in Section E4 of the 2001 NASPEC. On this basis, it is recommended that the current language in the 2001 NASPEC be revised to specify, if necessary, limits on manufacturer computed safety and resistance factors. Finally, it is recommended that fastener tilt during screw shear strength tests be eliminated to facilitate an accurate evaluation of the shear strength of a fastener.

Web crippling strength of a steel sandwich panel with V-shaped webs

Steel sandwich panels with V-shaped web flutes (V-core panels) serve the structural functions of a proposed energy-efficient roof system for residential construction. Due to its intended use as a flexural member spanning between a ridge beam and a structural wall, and required slender webs for weight considerations, web crippling under end one-flange loading is a critical strength limit state for the V-core panels. Although the 2001 North American Specification for the Design of Cold-Formed Steel Structural Members provides a design procedure to address web crippling, those design rules were developed for members whose cross sections are different from that of V-core panels. Consequently, nine specimens were tested to collect data on V-core panels subjected to end one-flange loading. Test observations suggested that V-core panels behave very similarly to multi-web decks that are strapped and unfastened to the supports. Experimental data reported in the literature was used to modify the web crippling strength equation in the Specification to reflect these particular conditions. The modified equation was found to adequately predict the measured web crippling strength of V-core panels.

Flexural strength of cold-formed steel built-up box sections

Presented in this paper is a study involving finite element analysis to investigate the flexural strength of built-up box sections which have been extensively used in residential and commercial construction in North America. In the North American Specification for the Design of Cold-Formed Steel Structural Members [CSA, North American specification for the design of cold-formed steel structural members, S136, Canadian Standard Association, 2002], there is no guideline or design equation to calculate the flexural strength of this type of section. Both the Lightweight Steel Framing Design Manual [CSA, Supplement 2004 to the North American specification for the design of cold-formed steel structural members, S136, Canadian Standard Association, 2004] and Cold-Formed Steel Framing Design Guide [AISI, Cold-formed steel framing design guide", American Iron and Steel Institute, 1st ed., 2002, 2nd ed., 2007] have recommended that the flexural strength and moment of inertia of the built-up sections to be taken as the sum of the two components based on deflection compatibility of the components. However, this design approximation has yet to be justified by experimental or numerical study especially for the cases of eccentric and concentric loading. In this study, the proposed finite element model of the built-up box sections was validated with the experimental tests carried out by Beshara and Lawson [Beshara B, Lawson TJ. Built-up girder screw connection variation flexural tests, Internal Report, Dietrich Design Group, 2002]. The flexural strengths obtained from the finite element analysis were then compared with the nominal strength evaluated based on the current design method in order to assess its suitability. Parametric studies were carried out for more than 30 specimens to identify factors affecting the flexural strength of cold-formed steel built-up box sections. A recommendation is made for current design practice of evaluating the flexural strength of the box section when subjected to eccentric loading.

Direct Strength Design of Cold-Formed Purlins

The Limit States Australian/New Zealand Standard AS/NZS 4600:2005 and the North American Specification (NAS) for the Design of Cold-Formed Steel Structural Members 2001 (2004 Supplement) include the newly developed direct strength method of design (DSM). In both standards, the method presented (Chapter 7 of AS/NZS 4600:2005, Appendix 1 of NAS) is limited to pure compression and pure bending. The situation of combined bending and shear as occurs in a continuous purlin system is not considered. In order to extend the DSM to purlin systems, it is necessary to prescribe and calibrate a method for combined bending and shear. Eight different test series on purlin sheeting systems with single, double, and triple spans and both uplift and downwards load cases as well as screw and concealed sheeting have been performed at the University of Sydney over a 10-year period. As many of these tests consisted of continuous lapped purlins where combined bending and shear occurred at the purlin section just outside the end ...

Web Crippling of Cold-Formed Stainless Steel Tubular Sections

Experimental and theoretical investigations on cold-formed stainless steel tubular sections subjected to web crippling performed by the authors are summarized in this paper. The web crippling test results of cold-formed stainless steel tubular sections subjected to four loading conditions specified in the American and the Australian/New Zealand specifications are presented in this paper. Moreover, web crippling tests conducted under end and interior loading conditions to simulate a floor joist member seated on a solid foundation subjected to a concentrated load are also reported, and these loading conditions are not currently specified in the specifications. All of these test results are compared with the design strengths obtained using the American, the Australian/New Zealand and the European specifications for cold-formed stainless steel members as well as the North American specification for cold-formed carbon steel structural members. It is shown that the design strengths predicted by these specifications are either unconservative or very conservative for high strength stainless steel tubular sections. Hence, a unified web crippling equation with carefully calibrated coefficients for cold-formed stainless steel tubular sections is proposed. Furthermore, tests on combined bending and web crippling are also described in this paper. The test strengths are also compared with the design strengths obtained using the American and the Australian/New Zealand specifications. It is shown that the design strengths predicted by these specifications are generally conservative for tubular sections subjected to combined bending and web crippling. In addition, the yield line mechanism analysis is used to investigate the web crippling behaviour of cold-formed stainless steel tubular sections.

Experimental and numerical investigation of high strength stainless steel structures

The paper summarises research on high strength stainless steel tubular structures conducted at the University of Hong Kong, and the Hong Kong University of Science and Technology. Square and rectangular hollow sections were investigated. The test specimens were cold-rolled from high strength austenitic and duplex stainless steel sheets. The material properties of the test specimens were determined by tensile coupon tests at normal room and elevated temperatures. The initial geometric imperfection and residual stress of the specimens were measured. The experimental and numerical investigation focused on the design and behaviour of cold-formed high strength stainless steel structural members. The results were compared with design strengths calculated using the American, Australian/New Zealand and European specifications for cold-formed stainless steel structures.