Cold-formed Steel Structural Members Research Articles

Pilot study: lateral braced C-sections under bending

The overall behavior under uniform load of cold-formed steel C-sections assemblies was investigated. Each test assembly consisted of C-sections acting as beams having a track section to restrain its ends. A lateral brace to restrain the C-sections from rotation was provided at mid-span. To better understand the influence of the brace on the flexural behavior, an experimental investigation was carried out with particular emphasis placed on the study of the effect of the mid-span brace connection when wallboard was attached to the tension flange. The tested moment capacities are compared to predictions based on the 1996 edition American Iron and Steel Institutes' Specification for design of cold-formed steel structural members.

Shift of Effective Centroid of Channel Columns

In the design of pin-ended channel columns, it is necessary to account for the shift of the effective centroid caused by local buckling. The current American Iron and Steel Institute's 1996 Specification for the Design of Cold-Formed Steel Structural Members and the 1996 Australian/New Zealand standard Cold-Formed Steel Structures calculate the shift by use of effective widths. However, the ability of the effective width rules to accurately predict this shift has not been experimentally assessed. In this paper, recent tests on fixed-ended channel columns are used to obtain values of the shift of the effective centroid, including its variation with the applied load. It is concluded that effective width rules of the American and Australian specifications accurately predict the direction and magnitude of the shift of the effective centroid for plain channels but not for lipped channels with slender flanges. The paper proposes simple modifications to the current effective width rules that provide agreement between the measured and predicted shifts of the effective centroid for lipped channels. The modifications are shown to produce more accurate design strengths for lipped channel columns.

Crippling Capacity of Web Elements with Openings

Commonly used cold-formed steel sections utilized as either wall studs or floor joists contain web holes. The web holes may be factory punched or field cut. Because the Specification for the Design of Cold-Formed Steel Structural Members does not address the potential impact that a web hole can have on the structural integrity of the cold-formed steel member, research was necessary. Researchers at the University of Missouri-Rolla have explored the behavior of a flexural member that possesses a web hole. The scope of the UMR research includes flexure, shear, web crippling, and combinations thereof. The present paper will summarize the findings and design recommendations pertaining to web crippling resulting from either end-one-flange or interior-one-flange loading. The research determined that the paramount factors influencing the web crippling behavior were the relationship between the hole depth and the depth of the web and the relationship between the distance from the edge of the bearing and the flat depth of the web. Easily applied design relationships have been developed.

The behaviour of cold-formed stainless steel structural members

The behaviour of cold-formed stainless steel structural members

Effective design width for perforated cold-formed steel compression members

Perforations are often provided in the web and (or) flange plates of beams and columns of cold-formed steel (CFS) structural members in order to facilitate duct work, piping, and bridging. This paper is concerned with the establishment of effective design width equations for the determination of the ultimate strength of such perforated members in compression. A proven finite element model has been used to study the effects of perforation parameters on the ultimate strength of perforated members. The finite element model consists of short columns of lipped channel CFS sections, discretized using nonlinear "assumed strain" shell finite elements, and utilising experimental-based material properties models. The parametric study covers web slenderness values between 31 and 194, perforation width to web width ratios up to 0.6, and perforation height to perforation width ratios up to 3.0. Effective design width equations for plates having square perforations and elongated perforations were developed. The efficiency and accuracy of these two equations in predicting the ultimate strength of perforated CFS compression members have been verified through a comparison with the ultimate load results of several experimental studies from the literature.Key words: cold-formed steel, compressive loads, local buckling, perforations, finite element analysis, experimental, post-buckling strength, ultimate strength, effective width, design.

Material Properties Models for Analysis of Cold-Formed Steel Members

The development and accuracy of an appropriate analytical model to predict the behavior of cold-formed steel (CFS) structural members necessitate a correct representation of the corresponding material characteristics. The results of two series of experimental investigations to evaluate the mechanical properties and the built-in residual stresses of CFS sections are reported in this paper. These investigations were performed on channel-shaped CFS sections manufactured using the cold-roll forming technique. Tensile coupon tests were used to evaluate the mechanical properties at different locations such as flat area, and the corner areas, of the channel sections. Electrical resistance strain gauges with an “electrical discharge machining” cutting technique were used to establish the magnitudes and the distributions of residual stresses within the channel sections. Based on the experimental results, appropriate analysis models for the stress-strain relationship, the variation of the yield strength, and the re...

University of Missouri-Rolla research on cold-formed steel structures

During the past 27 years, numerous research projects have been conducted at the University of Missouri-Rolla (UMR) under the sponsorships of the American Iron and Steel Institute, National Science Foundation, American Society of Civil Engineers, Metal Building Manufacturers Association, Steel Deck Institute, Metal/Lath Steel Framing Association, Chromium Center, Nickel Development Institute, and several steel companies located in the USA, Canada, and South Africa. The purpose of these investigations has been to study the structural strength of cold-formed steel members, connections, and structural systems. Some of the research findings have been used in the development of the AISI Specification for the Design of Cold-Formed Steel Structural Members, the AISI Automotive Design Manual, and the ASCE Standard Specification for the Design of Cold-Formed Stainless Steel Structural Members. This paper reviews the research work and other related activities on cold formed steel structures conducted at UMR.

Explicit Approach to Design of Stainless Steel Columns

The paper describes a design procedure for stainless-steel columns failing by flexural buckling. In the approach, the stress-strain curve is assumed to be expressed as a Ramberg-Osgood curve, defined in terms of the initial modulus (\iE\d0), the 0.2% proof stress (σ\d0\d.\d2), and the parameter \in. It is shown that the column curve can be described in terms of the Ramberg-Osgood parameters by adopting a Perry curve as the basic strength curve, and expressing the imperfection parameter in terms of \iE\d0, σ\d0\d.\d2, and \in. By using a Perry curve, the design procedure is explicit. This contrasts with the iterative approach described in the ASCE load and resistance factor design (LRFD) specification for the design of cold-formed stainless steel structural members. The proposed strength curves are compared with those from tests on stainless steel columns. It is shown that the coefficient of variation of the ratio of test strength to design strength is lower using the proposed design approach than when using the ASCE specification; thus, the proposed approach is more accurate than that described in the ASCE specification. It is also more efficient because it is explicit. Using the comparison with test results, the resistance factor to be used with the proposed design procedure is derived.

The accuracy of some codes of practice in predicting the load capacity of cold-formed columns

The accuracy of existing codes of practice for the design of cold formed steel sections, namely, from AISI [American Iron and Steel Institute. The Specification for the Design of Cold-formed Steel Structural Members (Aug. 1986)], BS (British Standards Institution. BS5950: Part 5—Structural Use of Steelwork in Building. Code of Practice for Design of Cold Formed Sections (1987).] and EUR [European Convention for Constructional Steelwork, ECCS. European Recommendations for the Design of Light Gauge Steel Members. Design of Cold Formed Steel Sheeting and Sections (1987).] is examined. Selected experimental results (ultimate load capacity) on columns with different cross-sections were used to compare with the predictions by the codes of practice. Results show that the accuracy of all the codes of practice examined varies from section to section. Some recommendations and proposed modifications to the codes were also made.

Web crippling of stainless steel cold-formed beams

The results of an investigation on the web crippling strength of cold-formed, stainless steel channel sections are presented in this paper. The stainless steels under consideration are AISI Types 304, 430 and a modified Type 409, designated Type 3CR12 corrosion-resisting steel. The lipped channel sections were manufactured by a press braking process. Beams were tested in pairs, lips facing, in an exterior-one-flange loading configuration. Experimental results were compared with the theoretical predictions given in the 1991 edition of the Specification for the Design of Cold-Formed Stainless Steel Structural Members. It was concluded in this study that the experimental results compare reasonably well with the theoretical predictions. For longer bearing lengths the theoretical strengths appear to be conservative.

Design approaches for cold-formed steel structures in the People's Republic of China

This paper briefly describes the limit state design method for cold-formed steel structures in China. Some basic factors affecting the structural safety, such as the reliability index, partial coefficients for loads and resistances etc. and design general expression are systematically discussed and presented. Besides, the design method for various cold-formed steel structural members and connections adopted by current Chinese Specification (GBJ 18–87) are also given in the text.

Cold-formed steel members — design approaches in the United States

In the United States, design specifications for cold-formed steel structural members have been developed and refined over a period of 50 years or so by a consensus group managed by the American Iron and Steel Institute (AISI). Recently, the scope of these specifications has broadened significantly. The traditional allowable stress design (ASD) specification for carbon and high-strength steel sheets was extensively revised in 1986 to reflect an allowable member moment or load approach. Referred to as the unified approach, the revised specification treats all types of compression elements with a consistent effective width approach and treats all types of compression members in a consistent manner. The specification was further modified by a 1989 addendum to reflect the results of continuing research. In 1991, the ASD specification was supplemented by a separate load and resistance factor design specification (LRFD), intended to provide a more consistent index of structural reliability. The ASD and LRFD specifications of the AISI have been organized on a parallel basis to facilitate consolidation at an appropriate date. Also, as discussed in a separate paper, a new specification for the design of cold-formed stainless steel members has been recently developed by a consensus group under the auspices of the American Society of Civil Engineers (ASCE). This ASCE document, which replaces an AISI ASD specification that had not been updated for many years, is an LRFD specification that includes an appendix with the ASD approach. Thus, specification development for the design of cold-formed members in the USA has been very active. This is made possible not only by the efforts of the supporting groups, but by the extensive volunteer efforts of the many engineers who participate.

Utilization of Cold Work in Cold-Formed Steel

An analysis to predict the yield strength of corners in cold-formed steel structural members was presented by Karren in 1967. It is based on plastic theory, using isotropic power-law strain hardening with von Mises’ yield condition and plastic potential. The analysis and consequent design formulas are quite complicated. This paper presents an alterative elementary analysis; specific assumptions of isotropy, von Mises’ yield condition, and isotropic power-law strain hardening has been relaxed. The solution is specialized for the case of linear strain hardening, leading a simple and perspicuous design formula. The proposed formula gives practically the same result as existing code procedures.

Structural Behavior of Thick Cold-Formed Steel Members

A study was made on the use of the “Specification for the Design of Cold-Formed Steel Structural Members” of the American Iron and Steel Institute (AISI) for the design of steel members cold-formed from thick sheets and plates. Experiments were conducted to study the increase in yield point caused by the cold work of forming. The investigation indicates that the design formulas for determining the effective design width of stiffened elements and the allowable stress for unstiffened compression elements currently included in the AISI Specification can be conservatively used for sections cold-formed from thick sheets and plates. It was also found that the AISI design provision for computing corner yield point provides good results for thick steel sheets and plates having a sharp yielding stress-strain curve with a small plateau and for cold-rolled sheets and strip.

Cold-Formed Steel Members with Perforated Elements

In cold-formed steel structural members, holes are sometimes provided in webs, or flanges, or both of beams and columns for duct work, piping, ease of handling, and for other purposes. The presence of such holes may result in a reduction in strength of individual component elements or the overall strength of the member, or in both. At present, only a limited amount of design information is available for relatively heavy steel sections with perforated elements; however, no provisions are included in the American Iron and Steel Institute specification for the design of cold-formed steel members with perforated elements. The structural behavior of cold-formed steel beams and columns with a single circular or square hole in the web or flange has been studied in this preliminary investigation. Design formulas subject to a limited scope have been developed from this study for possible determination of effective design width and load-carrying capacities.

Optimization of light-gage cold-formed steel shapes by parametric bandwidth constriction

Optimization of structural shapes governed by the American Iron and Steel Institute Specification for the Design of Cold-Formed Steel Structural Members presents particular problems. Not only must a variety of buckling formulas be considered for flexural-torsional buckling of the shape as a whole as well as for buckling of the separate plate elements of the cross-section, but also the section properties used to evaluate buckling stress constraints are themselves stress dependent. A simplicial technique is detailed for forcing convergence to competitive designs in spite of the iterative computational oscillations caused by the nonlinear complexity and discontinuities that are present in the mathematical programming problem which must be solved. The set of constraints includes all applicable and unmodified design formulas appearing in the AISI specification. The technique is a two-phase process which gradually constricts the range limits of the design parameters as observed over a set number of iterations and adaptively relieves cyclic infeasibilities caused by the constriction. Convergence is also aided by the use of a character string manipulation language to generate machine readable expressions for the exact differentials of all nonlinear functions. The behavior of the convergence forcing technique is demonstrated for a lipped Z shape in flexure and for a two-channel lipped wide flange beam column.

Minimum Weight Design of Light Gage Steel Members

Light gage steel is used extensively in light construction components. Large tonnages of a standard design are commonly produced, thus the minimum material requirements are of utmost importance to the product designer. A technique is presented for designing a minimum weight member to support a given loading condition. The problem is treated as a numerical optimization problem in which the variables are the dimensions and thickness of a given type of cross-sectional shape. Design requirements are based on the American Iron and Steel Institute Specification for the Design of Cold-Formed Steel Structural Members, 1968 Edition. These requirements are used to calculate a minimum acceptable thickness for a section whose other dimensions are considered temporarily fixed. This establishes the minimum weight design for the particular set of dimensions. Search methods are then employed to systematically establish sets of dimensions yielding reduced weight sections. Both a direct search and gradient search were examined and the latter found to be more efficient.