Cold-formed 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.

[3] The use of cold-formed steel members in building construction began in the 1850s in both the United States and Great Britain.

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,[5] the joists were adequate to carry the initial loads and spans, based on current analysis techniques.

Cold-formed steel members maintain a constant thickness around their cross-section, whereas hot-rolled shapes typically exhibit tapering or fillets.

[6] 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 [2] since 1939.

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).

[10] 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).

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.

Other nations utilize various design specifications, many based on AISI S-100, as adopted by the building codes listed below.

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 .

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.

Some of the main properties of cold formed steel are as follows:[13] A broad classification of the cold-formed shapes used in the construction industry can be made as individual structural framing members or panels and decks.

The ultimate tensile strength of steel sheets in the sections has little direct relationship to the design of those members.

Studies indicate that the effects of cold work on formed steel members depend largely upon the spread between the tensile and the yield strength of the virgin material.

The ductility criteria and performance of low-ductility steels for cold-formed members and connections have been studied by Dhalla, Winter, and Errera at Cornell University.

Uniform ductility is the ability of a tension coupon to undergo sizeable plastic deformations along its entire length prior to necking.

In order to be able to redistribute the stresses in the plastic range to avoid premature brittle fracture and to achieve full net-section strength in a tension member with stress concentrations, it is suggested that: Weldability refers to the capacity of steel to be welded into a satisfactory, crack free, sound joint under fabrication conditions without difficulty.

In high-rise commercial and multi-family residential construction, CFSF is typically used for interior partitions and support of exterior walls and cladding.

With this, it means getting all components of a Cold Rolled frame and a galvanised finish with no need for additional coating or painting.

[16] Connectors are used in cold-formed steel construction to attach members (i.e. studs, joists) to each other or to the primary structure for the purpose of load transfer and support.

Since an assembly is only as strong as its weakest component, it is important to engineer each connection so that it meets specified performance requirements.

Connectors may be fastened to cold-formed steel members and primary structure using welds, bolts, or self-drilling screws.

Annealing, also described in the earlier section, is part of the manufacturing process of cold-formed steel sheet.

An increase in prediction confidence stems from forced compatibility between section flanges and web throughout elastic buckling analysis.

This increase in prediction accuracy for any section geometry provides a solid basis for rational analysis extension and encourages cross-sectional optimization.

Either DSM or the main specification can be used with confidence as the Φ or Ω factors have been designed to insure that both methods are accurate.

Rational analysis is permitted when using optimized cold form shapes that are outside of the scope of the main specification and are not pre-qualified for DSM use.

There are currently no provisions within the DSM that pertain to shear, web crippling, holes in members, or strength increases due to the cold work of forming.

The finite strip method using CUFSM is the most commonly used approach to determine the elastic buckling loads.