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Structural steel is steel construction material, a profile, formed with a specific shape or cross section and certain standards of chemical composition and mechanical properties. Structural steel shape, size, composition, strength, storage, etc., is regulated in most industrialized countries. Structural steel members, such as I-beams, have high second moments of area, which allow them to be very stiff in respect to their cross-sectional area. Contents Common structural shapes Standards Typical grades are described as 'S275J2' or 'S355K2W'. In these examples, 'S' denotes structural rather than engineering steel; 275 or 355 denotes the yield strength in newtons per square millimetre or the equivalent megapascals; J2 or K2 denotes the materials toughness by reference to Charpy impact test values; and the 'W' denotes weathering steel. Further letters can be used to designate fine grain steel ('N' or 'NL'); quenched and tempered steel ('Q' or 'QL'); and thermomechanically rolled steel ('M' or 'ML'). The normal yield strength grades available are 195, 235, 275, 355, 420, and 460, although some grades are more commonly used than others e.g. in the UK, almost all structural steel is grades S275 and S355. Higher grades are available in quenched and tempered material (500, 550, 620, 690, 890 and 960 - although grades above 690 receive little if any use in construction at present). A set of euronorms define the shape of a set of standard structural profiles: European I-beam: IPE - Euronorm 19-57 The standard commonly used structural steels are:[1] Carbon steels Because steel components are “safety critical”, CE Marking is not allowed unless the Factory Production Control (FPC) system under which they are produced has been assessed by a suitable certification body that has been approved to the European Commission.[2] In the case of steel products such as sections, bolts and fabricated steelwork the CE Marking demonstrates that the product complies with the relevant harmonized standard.[3] For steel structures the main harmonized standards are: Steel sections and plate - EN 10025-1 Steel vs. concrete While rebar is almost always steel, it is not considered a structural steel and is described separately in the reinforcement bar and reinforced concrete articles. While both steel structures and reinforced concrete cement (R.C.C) structures have their pros and cons, the steel structures have better strength-to-weight ratios than RCC and can be easily dismantled. Steel structures, which have bolted connections, can also be reused to some extent after dismantling. Thermal properties The austenizing temperature, the temperature where a steel transforms to an austenite crystal structure, for steel starts at 900°C for pure iron, then, as more carbon is added, the temperature falls to a minimum 724°C for eutectic steel (steel with only .83% by weight of carbon in it). As 2.1% carbon (by mass) is approached, the austenizing temperature climbs back up, to 1130°C. Similarly, the melting point of steel changes based on the alloy. The lowest temperature at which a plain carbon steel can begin to melt, its solidus, is 1130 °C. Steel never turns into a liquid below this temperature. Pure Iron ('Steel' with 0% Carbon) starts to melt at 1492 °C (2720 °F), and is completely liquid upon reaching 1539 °C (2802 °F). Steel with 2.1% Carbon by weight begins melting at 1130 °C (2066 °F), and is completely molten upon reaching 1315 °C (2400 °F). 'Steel' with more than 2.1% Carbon is no longer Steel, but is known as Cast iron.[5] Fire resistance Concrete building structures often meet code required fire-resistance ratings, as the concrete thickness over the steel rebar provides sufficient fire resistance. However, concrete can be subject to spalling, particularly if it has an elevated moisture content. Although additional fireproofing is not often applied to concrete building structures, it is sometimes used in traffic tunnels and locations where a hydrocarbon fuel fire is more likely, as flammable liquid fires provides more heat to the structural element as compared to a fire involving ordinary combustibles during the same fire period. Structural steel fireproofing materials include intumescent, endothermic and plaster coatings as well as drywall, calcium silicate cladding, and mineral or high temperature insulation wool blankets. Attention is given to connections, as the thermal expansion of structural elements can compromise fire-resistance rated assemblies. Manufacturing A beam drill line (drill line) has long been considered an indispensable way to drill holes and mill slots into beams, channels and HSS elements. CNC beam drill lines are typically equipped with feed conveyors and position sensors to move the element into position for drilling, plus probing capability to determine the precise location where the hole or slot is to be cut. For cutting irregular openings or non-uniform ends on dimensional (non-plate) elements, a cutting torch is typically used. Oxy-fuel torches are the most common technology and range from simple hand-held torches to automated CNC coping machines that move the torch head around the structural element in accordance with cutting instructions programmed into the machine. Fabricating flat plate is performed on a plate processing center where the plate is laid flat on a stationary 'table' and different cutting heads traverse the plate from a gantry-style arm or "bridge." The cutting heads can include a punch, drill or torch. See also References
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