Steel Institute Specification Research Articles

Cold-Formed Steel Equal Angles with Complex Edge Stiffeners under Axial-Compression Laboratory Testing, Numerical Simulation, and Design

This paper investigates the axial-compression capacity of cold-formed steel (CFS) equal angle sections with complex edge stiffeners. Both experimental and numerical analyses were carried out. In total, 10 tests were carried out and the results are presented in this paper. Preceding to compression tests, the material properties were determined and initial geometric imperfections of all the test specimens were measured. From the results of compression tests, the specimens were all susceptible to flexural buckling. A numerical model was created using the finite-element (FE) software ABAQUS version 6.11. The results of finite-element analysis (FEA) substantiated with the experimental results. The FE models were found to accurately predict the experimental behavior. Thus, the validated FE models were used for a parametric study to analyze the effect of slenderness ratio and the orientation of edge stiffeners on the axial capacity. The axial strengths obtained from parametric study were compared with the design strengths calculated by the direct strength method (DSM) from the American Iron and Steel Institute (AISI) specification. Upon comparison, it was found that the axial strengths calculated based on the current DSM are overconservative by 58% on an average.

Modifications to the Direct Strength Method of cold-formed steel design for members unsymmetric about the axis of bending

The Direct Strength Method (DSM) has been an available option for the design of cold-formed steel members in the American Iron and Steel Institute (AISI) specification since 2004. The strength of flexural members unsymmetric about the bending axis presents some challenges related to post-buckling stress redistribution, which are not fully addressed in DSM today. This paper introduces generalized modifications to the DSM strength curves to improve strength prediction for these cases. Simple adjustments for stress redistribution due to both yielding and buckling are introduced and validated against a variety of section types from various published test and simulation results. An alternate solution is also developed utilizing a novel form of the strength equation which incorporates inelastic reserve strength. Both methods provide improvement to strength predictions suitable for consideration in design specifications.

Finite element analysis and proposed design rules for cold-formed stainless steel channels with web holes under end-one-flange loading

This paper presents a finite element analysis of cold-formed stainless steel channels with circular web holes, subjected to end-one-flange loading condition. The material properties of stainless steel types EN 1.4509 (Ferritic), EN 1.4462 (Duplex) and EN 1.4301 (Austenitic) were taken from the literature. To investigate the effect of web hole size, web hole location and bearing length on the web crippling strength of such sections, a parametric study involving a total of 1728 FE models was performed. The parametric study results were used to propose new web crippling strength equations and strength reduction factor equations which outperformed the equations of American Society of Civil Engineers Specification (ASCE 8–02), American Iron and Steel Institute Specification and Australia/New Zealand Standard (AISI&AS/NZS) and Lian et al (2016). A reliability analysis was then performed, which showed that the proposed design equations can closely predict the web crippling strength of cold-formed stainless steel channels with and without web holes under end-one-flange loading condition.

Distortional Buckling of Cold-Formed Steel Flanges under Stress Gradient

The strength of cold-formed steel beams with stiffened flanges may be controlled by distortional buckling. Buckling stress prediction methods have been developed for flanges under uniform compression. However, channel sections are commonly used where bending occurs about the minor axis with flanges under a stress gradient, such that the edges that are in compression and the flanges may experience distortional buckling. Current design specifications do not explicitly address this failure mode, which could lead to unsafe designs. This paper presents and verifies an analytical approach for distortional buckling stress prediction for flanges under a stress gradient. The approach is consistent with the design method used for flanges under uniform compression in the American Iron and Steel Institute (AISI) specification for the design of cold-formed steel members. This consistency facilitates a straightforward incorporation into the design specification.

Numerical simulation and specification provisions for buckling characteristics of a built-up steel column section subjected to axial loading

The demand for lightweight materials in construction has become very popular due to its flexibility and economical importance. Cold-formed steel beams and columns are used for provision of lightweight, durable and cost-efficient structures, and its usage also helps to optimize the construction time. Cold-formed steel section exhibits post-buckling strength, in which hot rolled section is deficient. However, more theoretical background on design and behavior of cold form section is still required, especially when it is subjected to axial loading. Thus, this paper presents numerical and theoretical behavior of pin -jointed cold-formed steel (CFS) column section (built-up battened Lip channel) under axial loading. The numerical modeling was done by using ABAQUS 6.10 software. Based on American Iron and Steel Institute (AISI) specifications, two types of sections were selected for single lipped channel, and it was ensured that the selected chord spacing permits both moment of inertia about the major axis and minor axis are equal. The numerical and theoretical study were done using a varying batten number and section slenderness ratio. The ultimate loads were obtained under the two approaches, for the lipped channel built-up columns, and were compared for the effective section proposed. From the results, the prediction of buckling mode and the failure load of the column were found to be stable and approximately relevant to the FEM results from slenderness ratio ranging from 20 to 60. Also, flexural buckling of all column sections occurred about the axis parallel to the webs, where there is an opportunity for composite action.

Structural behavior of self – drilling screws applied in steel structures of prefabricated buildings

Since the fast development of prefabricated building industry facilitate the light thin – walled steel application in both low residential building and fast construction, better understanding of the labour intensive fabrication of connection indicates the problems of optimized connection design and reduced manufacturing cost can be addressed. Several parameters such as number of screws and configurations of the screw layout were varied to study the impact on shear strength. Since the connection strength governs the structural behavior of the truss system which is the main part of modern thin – walled steel structure, the connection strength is calculated according to the American Iron and Steel Institute (AISI), Euro code, and Chinese specification respectively. The main failure mode occurred in self – drilling screw connections are found to be the tilting and bearing failure based on 84 single lap shear test. All testing specimens have experience four stages. When the spacing is fixed to certain number and the screw is less than six, the effect of configuration patter on the resistance capacity is very limited. In contrast, if the screw number is more than six, certain patter layout could lead to better overall strength compare with normal layout patter and the group effect factor is becoming as a constant. The strength of connection can be increased by enlarging the screw spacing with certain range.

Investigation on sheathing effect and failure modes of gypsum sheathed cold-formed steel wall panels subjected to bending

Sheathings and external covering becomes an essential part of the structures, especially when the structure is constructed using cold-formed steel (CFS). Conventionally, the contribution of attached sheathing was ignored in the design of the CFS structural members, but in the recent times, the sheathing effect is being incorporated in the design by American Iron and Steel Institute (AISI) specifications to improve the structural economy. A latest report by AISI titled “Sheathing Braced Design of Wall Studs - RP13-1” covers various sheathing configurations such as non-identical sheathings, single-sided sheathing, and fastener spacings. However, the validation of the AISI report for the flexural loading case is not yet carried out. Hence, a comprehensive investigation has been undertaken in the present work to address the effect of sheathing, associated failure modes, and appropriateness of AISI design specifications, when the sheathed CFS panel is subjected to bending. This paper presents the results of 12 full-scale (2400 mm long) CFS sheathed panels subjected to out-of-plane bending followed by design predictions using the current AISI specifications. Three different CFS studs based on global slenderness values (λe) were investigated with 4 different sheathing configurations. The experimental results indicate that the efficacy of sheathing increases with the increase in global slenderness of CFS studs. In addition, numerical studies of sheathed CFS wall panels based on a simple finite element modeling method suggested by the previous researchers is carried out, and the appropriateness of the model is verified. The design prediction results using the AISI specifications indicates that the effect of sheathing is overestimated, thereby leading to unconservative prediction for most of the sheathed CFS wall panel specimens.

Effect of stiffened element and edge stiffener in strength and behaviour of cold formed steel built-up beams

The aim of this study is to investigate the effect of stiffened element and edge stiffener in the behaviour and flexural strength of built-up cold-formed steel beams. An experimental and analytical analysis of CFS channel sections in four different geometries is conducted, including simple channel sections, a stiffened channel section with or without edge stiffeners. Nonlinear finite element models are developed using finite element analysis software package ANSYS. The FEA results are verified with the experimental results. Further, the finite element model is used for parametric studies by varying the depth, thickness, and the effect of stiffened element, edge stiffener and their interaction with compression flanges on stiffened built-up cold-formed steel beams with upright edge stiffeners. In addition, the flexural strength predicted by the finite element analysis is compared with the design flexural strength calculated by using the North American Iron and Steel Institute Specifications for cold-formed steel structures (AISI: S100-2007) and suitable suggestion is made.

Experimental testing of cold-formed built-up members in pure compression

Cold-formed built-up members are compression members that are common in multiple areas of steel construction, which include cold-formed steel joints and stud walls. These members are vulnerable to unique buckling behaviors; however, limited experimental research has been done in this area. Give this gap, experimental testing of 71 built-up members was conducted in this study. The variations of the test specimens include multiple lengths, intermediate welds, orientations, and thicknesses. The experimental testing was devised to observe the different buckling modes of the built-up C-channels and the effects of the geometrical properties; to check for applicability of multiple intermediate welding patterns; and to evaluate both the 2001 and 2007 editions of the American Iron and Steel Institute (AISI) Specification for built-up members in pure compression. The AISI-2001 and AISI-2007 were found to give inconsistent results that at times were un-conservative or overly conservative in terms of axial strength. It was also found that orientation of the member has an important impact on the maximum failure load on the member.

Behaviour of stiffened cold-formed steel built-up sections with complex edge stiffeners under bending

This paper is concerned with the effect of stiffened element at the flange/web junction and complex edge stiffener in behaviour and strength of built-up cold-formed steel flexural members. An extensive experimental investigation and a finite element analysis of stiffened built-up cold-formed beam sections with complex stiffeners under two point loading is presented. A nonlinear finite element model is developed and verified against test results. All the results are compared with the design strength calculated using the North American Iron and Steel Institute Specification for cold-formed steel structures (AISI: S100, 2007). Following the validation, an extensive finite element parametric study is conducted to study the influences of a range of parameters, and the results are compared with the nominal design strength by AISI: S100 (2007) and suitable recommendation are made.

Experiments on sheathed cold-formed steel studs in compression

The stability and strength of cold-formed steel lipped C-section columns (studs) with sheathing attached to the flanges is the subject of this paper. Stud configurations both with and without sheathing, either oriented strand board or gypsum board, are tested for failure in compression. A total of twenty-six tests covering short, intermediate and long specimens, varied sheathing configurations, and varied end boundary conditions are completed. Dimensions and geometric imperfections of the specimens are measured in detail. The measured geometric imperfections are reduced to scalar magnitudes consistent with local, distortional, and global buckling modes. During the testing, mid-height cross-section deformations are recorded using five position transducers. The deformations indicate the impact of the different combinations of sheathing, and of the end boundary conditions, on the strength and stability of the studs. Composite action between the stud and sheathing, and isolating direct loading of the sheathing, are shown to be significant in determining the strength and controlling limit state of the stud. Tested strengths are compared with existing North American (American Iron and Steel Institute) specification methods and potential improvements are explored.

Strength of biaxially loaded slender I-section beam-columns

The strength of a slender section is governed by local buckling of its elements. The local buckling mode is mainly affected by the width to thickness ratios of elements forming the section and the member slenderness ratio. A nonlinear finite element model was developed in this paper to study the effect of the mentioned factors on the capacity of biaxially loaded slender I-section beam–columns. A group of I sections was selected with varying flange width to flange thickness and web width to web thickness ratios. Different member slenderness ratios were chosen to study the different modes of failure. The results show that the linear interaction equation is safe and provides a good fit to the ultimate capacity of members with intermediate slenderness ratios. It is conservative, however, for short member slenderness ratios. Lastly, compared with the newly developed finite element model, the 1996 edition of the American Iron and Steel Institute specification for cold-formed steel structural members and the European Committee for Standardization Eurocode 3 conservatively predict the capacity of members, especially for large ratios of minor axis to major axis bending.Key words: structural engineering, steel, stability, buckling, biaxial loads, ultimate strength.

Compression Tests of Cold-Reduced High Strength Steel Sections. I: Stub Columns

This paper describes a series of compression tests performed on stub columns fabricated from cold-formed high strength steel plates with nominal yield stress of 550MPa. The steel is classified as G550 to Australia Standard AS1397. The test results presented in this paper are the first stage of an Australian Research Council research project entitled “Compression stability of high strength steel sections with low strain-hardening.” The tests include lipped-square and hexagonal sections, including 94 box-shaped fix-ended stub columns. The purpose of these tests was to determine the influence of low strain hardening of G550 steel on the compressive section capacities of the column members. The results of the successful stub column tests have been compared with the design procedures in the Australian/New Zealand Standard for Cold-Formed Steel Structures and recent (1999) amendments to the American Iron and Steel Institute Specification. As expected, the greatest effect of low strain hardening was for the stoc...

Web crippling of cold-formed unlipped channels with flanges restrained

The paper describes a series of web crippling tests on cold-formed unlipped channels with flanges restrained (fastened) as well as channels with flanges unrestrained (unfastened). The tests were performed under end and interior two-flange loading conditions specified in the North American Specification and Australian/New Zealand Standard for cold-formed steel structures, namely end-two-flange and interior-two-flange loading conditions. The concentrated load was applied by a bearing plate at the top flange of the channels, and the reaction force applied by an identical bearing plate at the bottom flange of the channels. The bearing plates acted across the full flange widths of the channels. The flanges of the channels were either bolted to one or two bearing plates for the specimens with flanges restrained. The web crippling test strengths are compared with the design strengths obtained using the North American Specification, Australian/New Zealand Standard and American Iron and Steel Institute Specification for cold-formed steel structures. It is shown that the design strengths predicted by the North American Specification using the unfastened design rules are generally conservative, but unconservatively predicted using the fastened design rules, even when the flanges of the specimens were restrained. The design strengths predicted by the Australian/New Zealand Standard and American Iron and Steel Institute Specification are unconservative.

Compression Tests of Channels with Inclined Simple Edge Stiffeners

The paper describes a series of tests on cold-formed channels with inclined simple edge stiffeners compressed between fixed ends. The simple edge stiffeners of the channel sections consist of simple lips. The new North American Specification and the Australian/New Zealand Standard for cold-formed steel structures provide design rules for channels with inclined edge stiffeners. However, the design rules are mainly based on tests of sections having edge stiffeners perpendicular to the flanges. The provisions for inclined edge stiffeners are determined based on intuition without rigorous experimental evidence. Hence, it is important to obtain test data for sections with edge stiffeners not perpendicular to the flanges. A series of compression tests was performed on cold-formed channels with inclined edge stiffeners. The edge stiffeners of the channels were inclined at different angles for both outwards and inwards. The distortional buckling mode, where the flange and lip rotate about the flange-web junction restrained by the web, was observed in all tests. The test strengths are compared with the design strengths predicted by the North American Specification, the American Iron and Steel Institute Specification, and the Australian/New Zealand Standard for cold-formed steel structures. For the North American Specification and the American Iron and Steel Institute Specification, the distortional buckling mode is not explicitly accounted for in design. However, the Australian/New Zealand Standard has explicit design rules for distortional buckling in addition to the edge stiffened design rules which are the same as the American Iron and Steel Institute Specification.

Cold-Formed Steel Channels Subjected to Concentrated Bearing Load

A test program on cold-formed steel channels subjected to concentrated bearing load is presented in this paper. The web slenderness values of the channel specimens ranged from comparatively stocky webs of 15.3 to relatively more slender webs of 62.7. The tests were performed under end and interior loading conditions. The test setup was different from the one specified in the North American Specification and the Australian/New Zealand Standard for cold-formed steel structures where the loading support is assumed free to rotate in the plane of the beam. The test specimens were seated on a fixed flat solid steel base plate, and a concentrated load was applied through a bearing plate to the top flange of the channels. The test setup simulates a floor joist member subjected to concentrated load. The test strengths are compared with the design strengths obtained using the North American Specification and the Australian/New Zealand Standard. It is concluded that the design strengths predicted by the North American Specification are generally conservative for end-two-flange and interior-two-flange loadings, and these design rules are shown to be reliable using reliability analysis. However, the design strengths predicted by the Australian/New Zealand Standard, that is similar to the American Iron and Steel Institute Specification, are generally unconservative.

Cold-formed steel structures

Abstract Cold-formed steel structures are steel structural products that are made by bending flat sheets of steel at ambient temperature into shapes which will support more than the flat sheets themselves. They have been produced for more than a century since the first flat sheets of steel were produced by the steel mills. However, in recent years, higher strength materials and a wider range of structural applications have caused a significant growth in cold-formed steel relative to the traditional heavier hot-rolled steel structural members. This paper contains three components. First, it reviews and summarises the major research developments in cold-formed steel structures over the last 3 years (1999–2001) as published in leading journals on steel structures and thin-walled structures. Secondly, it summarises the development of the North American Specification for the Design of Cold-Formed Steel Structural Members. Finally, it provides a brief summary of the Direct Strength Method being developed by the American Iron and Steel Institute Specification Committee.

Web Crippling Behavior of Floor Joist/Rim Members in Built Assemblies

This paper presents the results of a pilot study of the web crippling performance of two common exterior load-bearing wall conditions (rim joist and rim track with a framing joist) in light framed cold-formed (light-gauge) steel construction. The intent of the study was to develop some preliminary data on the web crippling performance of built assemblies. The test results show that the ultimate strength for the two web crippling conditions considered may be greater than the sum of the individual strengths of the components (based on current American Iron and Steel Institute Specification equations). Further, on the basis of the configurations tested, it appears that the measured higher strengths may be due to a beneficial distribution of load at the corners of a track section. The tests also showed that although the measured strengths may be high, the associated cross-sectional deformations tend to be relatively large. For gravity load design, this deformation may be treated as a serviceability limit stat...

Tests of Channels Subjected to Combined Bending and Web Crippling

An experimental investigation of cold-formed channels subjected to combined bending and web crippling is described in this paper. A series of tests was performed on unlipped channels rolled from high strength structural steel sheets having nominal plate thickness up to 6 mm, and a maximum web slenderness value of 45. This value is considerably lower than the intended web slenderness values used in the Australian/New Zealand Standard (AS/NZS 1996) and the American Iron and Steel Institute (AISI 1996) specification for cold-formed steel structures. Therefore, the appropriateness of the combined bending and web crippling design rules for members with comparatively stocky webs is investigated in this paper. The specimens were tested at various lengths using the Interior-One-Flange loading condition specified in the AS/NZS (1996) and the AISI (1996) specification, and the test strengths are compared with the design strengths obtained from these specifications. Generally, it is shown that the specifications conservatively predicted the strengths of unlipped channels having stocky webs subjected to combined bending and web crippling.

Neural Network Model for Uplift Load Capacity of Metal Roof Panels

The metal roofing industry uses a variety of commonly used methods to determine the structural performance (positive load capacity and negative or uplift load capacity) of various cold-formed metal roof panel configurations. The metal roof panel system considered in this paper consists of cold-formed U-shaped panels fabricated from 0.024-in. (0.61-mm) thick coated steel that are attached to cold-formed Z-shaped 0.060-in. (1.52-mm) thick coated steel purlins using concealed clips. Uplift capacity may be calculated for a given panel section according to the approach described in the American Iron and Steel Institute specifications. Its method for calculating load capacity of metal roofing systems is considered unreliable because it typically produces results dramatically different than results obtained from actual testing. A new method of determining the load capacity of U-shaped metal roof panel systems is presented using a counterpropagation neural network. The new method accounts for distortional changes...