Production
- Iron ore undergoes a process known as smelting in order to become the structural product known as steel.
- During this process, four materials (iron ore, flux, coke, and oxygen) are used to turn the dirtier iron ore into a wrought iron. The process occurs in a blast furnace where the coke (charcoal treated to remove impurities) is burned to create CO (carbon monoxide) that then reduces the ore into elemental iron. This then comes into contact with the flux (limestone or pure lime) that removes impurities from the steel to become slag. This mixture can be repurposed for paving certain kinds of roads or remade into structural-grade steel (as shown in One Bryant Park). The remaining iron left after reacting with the flux is now full of carbon that must be removed to produce structural steel.
- This new process is called the basic oxygen process. The molten iron is held in a container into which a lance is inserted. Pure oxygen is blown out of this lance to remove carbon from the iron which is continuously in contact with the flux.
- Steel that comes from recycled products (which includes most of the structural steel used in the United States) that is melted in an electric arc furnace and processed till it is acceptable for use in buildings.
- Once the steel has been produced, it is sent to a structural mill that processes the material through a series of rollers that produce the exact shapes necessary for building construction. Depending on the types of rollers used and their positioning during its processing different shapes of wide-flanges, angles, bars, channels and tees are produced, each with its own unique place in steel construction.
Steel Shapes
- Wide-Flange: also known as an I-beam, these are the most typical shapes used in steel construction. These elements are shaped to spread out the tensile and compressive elements involved when a beam or lintel is bending, placing little material where tension and compression are low (the middle of the beam) and a lot of material where these forces are high (the tops and bottoms of the beam.) It is because of this simple application of physics that wide-flanges have this particular shape.
- Steel Angles: these are often used as beams or incorporated into steel truss systems. When used as beams they can help a masonry wall span a gap in its construction, effectively acting as a lintel, or can do the same in steel framing. When used as a piece of a steel truss (also called and open-web steel joist) they are welded together to form the webs and braces necessary for a typical truss.
- Channels: these sometimes replace steel angles in truss systems or as lintels.
- Corrugated Steel Decking: Often seen used as roofing for sheds or pavilions, decking is also used in steel framing systems as flooring.
- Taller decking is used in roofing systems with flat insulation. Vertical loading is not a main concern in these types of systems.
- Shorter decking with ridges is typically used as flooring with concrete poured in place over the steel framing system. This decking is welded to the I-beams beneath to maintain a rigid connection with the structure.
Connections
- Pin Connection: These are created when a beam is bolted into a column. While this type of connection’s structural purpose is to connect the beam and the column, the only forces the connection can support are shear forces. This means that if there is high seismic activity or wind forces and the bolts in the connection are placed in tension, the connection will fail.
- Moment Connection: When the steal beam and column are welded together a moment (or rigid) connection is formed. This type of connection can transfer bending forces from the beam to the column and can withstand greater lateral loading than steel pin connections.