Cold-formed steel

Cold-formed steel (CFS) is the common term for steel products shaped by cold-working processes carried out near room temperature, such as rolling, pressing, stamping, bending, etc. Stock bars and sheets of cold-rolled steel (CRS) are commonly used in all areas of manufacturing. The terms are opposed to hot-formed steel and hot-rolled steel.

Cold-formed steel, especially in the form of thin gauge sheets, is commonly used in the construction industry for structural or non-structural items such as columns, beams, joists, studs, floor decking, built-up sections and other components. Such uses have become more and more popular in the US since their standardization in 1946.

Cold-formed steel members have been used also in bridges, storage racks, grain bins, car bodies, railway coaches, highway products, transmission towers, transmission poles, drainage facilities, firearms, various types of equipment and others. These types of sections are cold-formed from steel sheet, strip, plate, or flat bar in roll forming machines, by press brake (machine press) or bending operations. The material thicknesses for such thin-walled steel members usually range from 0.0147 in. (0.373 mm) to about ¼ in. (6.35 mm). Steel plates and bars as thick as 1 in. (25.4 mm) can also be cold-formed successfully into structural shapes (AISI, 2007b).

History

The use of cold-formed steel members in building construction began in the 1850s in both the United States and Great Britain. In the 1920s and 1930s, acceptance of cold-formed steel as a construction material was still limited because there was no adequate design standard and limited information on material use in building codes. One of the first documented uses of cold-formed steel as a building material is the Virginia Baptist Hospital,  constructed around 1925 in Lynchburg, Virginia. The walls were load bearing masonry, but the floor system was framed with double back-to-back cold-formed steel lipped channels. According to Chuck Greene, P.E., of Nolen Frisa Associates, the joists were adequate to carry the initial loads and spans, based on current analysis techniques. Greene engineered a recent renovation to the structure and said that for the most part, the joists are still performing well. A site observation during this renovation confirmed that "these joists from the 'roaring twenties' are still supporting loads, over 80 years later!" In the 1940s, Lustron Homes built and sold almost 2500 steel-framed homes, with the framing, finishes, cabinets and furniture made from cold-formed steel.

History of AISI design standards

Design standards for hot-rolled steel (see structural steel) were adopted in 1930s, but were not applicable to cold–formed sections because of their relatively thin steel walls which were susceptible to buckling. Cold-formed steel members maintain a constant thickness around their cross-section, whereas hot-rolled shapes typically exhibit tapering or fillets. Cold-formed steel allowed for shapes which differed greatly from the classical hot-rolled shapes. The material was easily workable; it could be deformed into many possible shapes. Even a small change in the geometry created significant changes in the strength characteristics of the section. It was necessary to establish some minimum requirements and laws to control the buckling and strength characteristics. Also it was observed that the thin walls underwent local buckling under small loads in some sections and that these elements were then capable of carrying higher loads even after local buckling of the members.

In the United States, the first edition of the Specification for the Design of Light Gage Steel Structural Members was published by the American Iron and Steel Institute (AISI) in 1946 (AISI, 1946). The first Allowable Stress Design (ASD) Specification was based on the research work sponsored by AISI at Cornell University under the direction of late Professor George Winter  since 1939. As a result of this work, George Winter is now considered the grandfather of cold-formed steel design. The ASD Specification was subsequently revised in 1956, 1960, 1962, 1968, 1980, and 1986 to reflect the technical developments and the results of continued research at Cornell and other universities (Yu et al., 1996). In 1991, AISI published the first edition of the Load and Resistance Factor Design Specification developed at University of Missouri of Rolla and Washington University under the directions of Wei-Wen Yu  and Theodore V. Galambos (AISI, 1991). Both ASD and LRFD Specifications were combined into a single specification in 1996 (AISI, 1996).

In 2001, the first edition of the North American Specification for the Design of Cold-Formed Steel Structural Members was developed by a joint effort of the AISI Committee on Specifications, the Canadian Standards Association (CSA) Technical Committee on Cold-Formed Steel Structural Members, and Camara Nacional de la Industria del Hierro y del Acero (CANACERO) in Mexico (AISI, 2001). It included the ASD and LRFD methods for the United States and Mexico together with the Limit States Design (LSD) method for Canada. This North American Specification has been accredited by the American National Standard Institute (ANSI) as an ANSI Standard to supersede the 1996 AISI Specification and the 1994 CSA Standard. Following the successful use of the 2001 edition of the North American Specification for six years, it was revised and expanded in 2007.

This updated specification includes new and revised design provisions with the additions of the Direct Strength Method in Appendix 1 and the Second-Order Analysis of structural systems in Appendix 2.

In addition to the AISI specifications, the American Iron and Steel Institute has also published commentaries on various editions of the specifications, design manuals, framing design standards, various design guides, and design aids for using cold-formed steel. For details, see AISI  website.

International codes and standards

The United States, Mexico and Canada use the North American Specification for the Design of Cold-Formed Steel Structural Members, document number AISI S100-2007. Member states of the European Union use section 1-3 of the Eurocode 3 (EN 1993) for the design of cold formed steel members. Other nations utilize various design specifications, many based on AISI S-100, as adopted by the building codes listed below. Another list of international cold-formed steel codes and standards is maintained (and can be edited with permission) at Cold-Formed Steel Codes Around the World.

Africa

Ethiopia Building Codes: EBCS-1 Basis of design and actions on structures EBCS-3 Design of steel structures

South Africa Specification: SANS 10162 - The Structural Use of Steel: Part 2 - Limit-state design of cold-formed steelwork Building code: National Building Regulations of South Africa

Americas

United States Specification: North American Specification for the Design of Cold-Formed Steel Structural Members, document number AISI S100-2007 published by the American Iron and Steel Institute in October 2007. Building Code: IBC and/or NFPA may be enforced, but both reference AISI S100.

Canada Specification: North American Specification for the Design of Cold-Formed Steel Structural Members, document number CAN/CSA S136-07 as published by Canadian Standards Association which is the same as AISI S100 except for the cover. Building Code: The National Building Code of Canada is the model code adopted with amendments by individual Provinces and Territories. The Federal government is outside the jurisdiction of the Provincial/Territorial authority but usually defers to the legislated requirements within the Province/Territory of the building site.

Brazil Specification: NBR 14762:2001 Dimensionamento de estruturas de aço constituídas por perfis formados a frio - Procedimento (Cold-formed steel design - Procedure, last update 2001) and NBR 6355:2003 Perfis estruturais de aço formados a frio - Padronização (Cold-formed steel structural profiles, last update 2003) Building Code: ABNT - Associação Brasileira de Normas Técnicas

Chile NCH 427 - suspended because it was written in the 1970s. Cold-formed steel sections were based in part on AISI (U.S). The local Institute for Building code INN has specified in recent Codes for seismic design that designers must use the last edition of the AISI Specification for cold formed steel and the AISC for hot rolled, in their original versions in English until some traduced adaption will be issued here .

Argentina CIRSOC 303 for Light Steel Structures where cold formed steel is included. That Specification, now more than 20 years old, is being replaced by a new one, which will be, in general, an adaption of the current AISI one. The former CIRSOC 303 was an adaption of the Canadian code of that time. At this time CIRSOC 303 was very old, now CIRSOC 301 is in revolution to be aligned with the American codes (LRFD design). In the near future both codes will be aligned also in designations and terminology.

Asia

Philippines National Structural Code of the Philippines 2010, Volume 1 Buildings, Towers, and other Vertical Structures, Chapter 5 Part 3 Design of Cold-Formed Steel Structural Members is based on AISI S100-2007

India Specification:IS:801, Indian standard code of practice for use of cold-formed light gauge steel structural members in general building construction, Bureau of Indian Standards, New Delhi (1975). (currently under revision) Building Code : see - model code National Building Code of India

China Specification: Technical Code of Cold-formed Thin-wall Steel Structures Building Code: GB 50018-2002 (current version)

Japan Specification: Design Manual of Light-gauge Steel Structures Building Code: Technical standard notification No.1641 concerning light-gauge steel structures

Malaysia Malaysia uses British Standard BS5950, especially BS5950:Part 5; AS4600 (from Australia) is also referenced.

Europe

EU Countries Specification: EN 1993-1-3 (same as Eurocode 3 part 1-3), Design of steel structures - Cold formed thin gauge members and sheeting. Each European country will get its own National Annex Documents (NAD).

Germany Specification: German Committee for Steel Structures (DASt), DASt-Guidelines 016: 1992: Calculation and design of structures with thin-walled cold-formed members; In German Building Code: EN 1993-1-3: 2006 (Eurocode 3 Part 1-3): Design of steel structures – General rules – Supplementary rules for cold-formed members and sheeting; German version prEN 1090 2: 2005 (prEN 1090 Part 2; Draft): Execution of steel structures and aluminium structures – Technical requirements for the execution of steel structures; German version EN 10162: 2003: Cold-rolled steel sections – Technical delivery conditions – Dimensional and cross-sectional tolerances; German version