10 Cold Form Steel

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    Cold Form SteelConstructions Material Technology

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    That are cold formedsteel structures!!!

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    So what is cold formed steel ?

    Cold-formed steel (CFS) is the common term forproducts made by rolling or pressing thin gauges ofsheet steel into goods.

    Cold-formed steel goods are created by theworking of sheet steel using stamping, rolling, orpresses to deform the sheet into a usable product.

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    Cold-formed steel products are just what the nameconnotes: products that are made by bending a flatsheet of steel at room temperature into a shape

    that will support more load than the flat sheetitself.

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    The history

    The use of cold-formed steel members in buildingconstruction began in the 1850s in both the UnitedStates and Great Britain.

    In the 1920s and 1930s, acceptance of cold-formedsteel as a construction material was still limitedbecause there was no adequate design standard andlimited information on material use in building codes.

    One of the first documented uses of cold-formed steelas a building material is the Virginia Baptist Hospital,constructed around 1925 in Lynchburg, Virginia.

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    The history (continued)

    The walls were load bearing masonry, but the floorsystem was framed with double back-to-back cold-formed steel lipped channels.

    According to Chuck Greene, P.E of Nolen FrisaAssociates, the joists were adequate to carry theinitial loads and spans, based on current analysistechniques.

    Greene engineered a recent renovation to thestructure and said that for the most part, the joistsare still performing well.

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    The history (continued)

    A site observation during this renovation confirmedthat "these joists from the 'roaring twenties' arestill supporting loads, over 80 years later!" In the

    1940s, Lustron Homes built and sold almost 2500steel-framed homes, with the framing, finishes,cabinets and furniture made from cold-formedsteel.

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    The process of making

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    The benefit As compared with thicker hot-rolled shapes, coldformed light members can bemanufactured for relatively light loads and/or short spans.

    Unusual sectional configurations can be produced economically by cold-formingoperations, and consequently favorable strength-to-weight ratios can be obtained.

    Nestable sections can be produced, allowing for compact packaging and shipping.

    Load-carrying panels and decks can provide useful surfaces for floor, roof, and wallconstruction, and in other cases they can also provide enclosed cells for electrical andother conduits.

    Load-carrying panels and decks not only withstand loads normal to their surfaces, butthey can also act as shear diaphragms to resist force in their own planes if they areadequately interconnected to each other and to supporting members.

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    The benefit (continued ) Compared with other materials such as timber and concrete, the

    following qualities can be realized for coldformed steel structuralmembers

    1. Lightness2. High strength and stiffness

    3. Ease of prefabrication and mass production4. Fast and easy erection and installation5. Substantial elimination of delays due to weather6. More accurate detailing7. Non-shrinking and non-creeping at ambient temperatures8. Formwork unneeded

    9. Termite proof and rot proof 10. Uniform quality11. Economy in transportation and handling12. Non-combustibility13. Recyclable material

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    Typical stressstrain propertiesA main property of steel, which is used to describe its behavior, is the stressstraingraph. The stressstrain graphs of cold-formed steel sheet mainly fall into twocategories. They are sharp yielding and gradual yielding type illustrated below in Fig.1and Fig.2, respectively.

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    These two stressstrain curves are typical for cold-formed steel sheet during tension test.The second graph is the representation of the steel sheet that has undergone the cold-reducing (hard rolling) during manufacturing process, therefore it does not exhibit a yieldpoint with a yield plateau. The initial slope of the curve may be lowered as a result of theprework. Unlike Fig.1, the stressstrain relationship in Fig.2 represents the behavior ofannealed steel sheet. For this type of steel, the yield point is defined by the level at whichthe stressstrain curve becomes horizontal.

    Cold forming has the effect of increasing the yield strength of steel, the increase being theconsequence of cold working well into the strain-hardening range. This increase is in thezones where the material is deformed by bending or working. The yield stress can be

    assumed to have been increased by 15% or more for design purposes. The yield stressvalue of cold-formed steel is usually between 33ksi and 80ksi. The measured values ofModulus of Elasticity based on the standard methods usually range from 29,000 to 30,000ksi (200 to 207 GPa). A value of 29,500 ksi (203 GPa) is recommended by AISI in itsspecification for design purposes. The ultimate tensile strength of steel sheets in thesections has little direct relationship to the design of those members. The load-carryingcapacities of cold-formed steel flexural and compression members are usually limited byyield point or buckling stresses that are less than the yield point of steel, particularly forthose compression elements having relatively large flat-width ratios and for compressionmembers having relatively large slenderness ratios. Studies indicate that the effects ofcold work on formed steel members depend largely upon the spread between the tensileand the yield strength of the virgin material.

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