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. 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). 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. It was necessary to establish some minimum requirements and laws to control the buckling and strength characteristics. Even a small change in the geometry created significant changes in the strength characteristics of the section. The material was easily workable it could be deformed into many possible shapes. Cold-formed steel allowed for shapes which differed greatly from the classical hot-rolled shapes. Cold-formed steel members maintain a constant thickness around their cross-section, whereas hot-rolled shapes typically exhibit tapering or fillets. History of AISI design standards ĭesign 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. 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. Greene engineered a recent renovation to the structure and said that for the most part, the joists are still performing well. 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. The walls were load bearing masonry, but the floor system was framed with double back-to-back cold-formed steel lipped channels. 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. 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. The use of cold-formed steel members in building construction began in the 1850s in both the United States and Great Britain. 9 Hot-rolled versus cold-rolled steel and the influence of annealing.8.2 Connectors and fasteners in framing.7.1 Minimum material thickness recommended for welding connections.4 Common section profiles and applications.When it is not done correctly, there are many ways in which the performance can be compromised.
When this is done, the cold formed steel system will deliver excellent structural performance. The fabricator must then build the system in accordance with the drawings.
It is not something that can or should be covered in AS/NZS 4600 but it relies on the experience of the design engineer to both perform an adequate design and then to document this to the fabricator so it gets built as the designer intended. This is vital in all steel construction and especially in multi-member connections in light steel framed systems. Only then can the designer be certain that the connection components carrying the loads can transfer these as intended. It is extremely important that the loads to be transferred through the connections are accurately quantified and the load paths well understood. This is especially the case where elements in a member cross section are removed to allow one member to connect into another. However, it is also a challenging material to design, especially at a system level and one in which the load transfer through connections must be very well understood and applied. Cold formed steel framing is an incredibly versatile material to work with and, properly designed and detailed, it delivers dependable structural solutions with a strength to weight ratio far superior to other structural materials.
I teach cold formed steel design at the University of Auckland and have been a technical advisor to NASH New Zealand since its formation in 1989.