Hot rolled steel sections are the most widely used sections and includes largest category of shapes available. Sections are chosen according to the structural design requirements and availability.
In a rolling mill, molten steel taken from the furnace is poured into a continuous casting system. According to the desirable properties needed in the structure, Steel is allowed to solidify. Solidified hot steel is passed through series of process and rollers that prepares the material into desired shape. When steel is rolled in hot state, there is almost no loss in ductility, when compared to cold rolling. After rolling, members are cut to length which can be transported and stored as needed.
Steel sections are mostly categorized according to their cross sectional shapes. Steel designers can make use of I.S. specs for weight, size, moduli, etc in selection of sections for their purpose. There are many types of sections available, most commonly used are: (a) Angle (b) I – Beam (c) Channel (d) Tees (e) Tubes (f) Flats (g) Bars (h) Sheets (i) Plates (j) Strips and many other variations.
Angle Section and I-Beam section were one of the first shapes produced in a rolling mill. At that time, these shapes were made of wrought iron. Terms Sheets and Plates are often used interchangeably; basic difference between Sheets and Plates is that Sheets are generally upto 4mm thick and Plates are minimum 5mm thick.
For illustration, a google search of steel sections gives this result:
When deciding thickness of steel sections, we need to look at the fact if the steel is exposed to weather, surface is available for cleaning and maintenance, surface contact with water and soil, etc. As a general rule, steel exposed to weather needs to be around 1-2 mm thicker. And an extra 1.5 mm thicker when in contact with water.
In most of the scenarios, sections mentioned above will be able to satisfy design requirements. For special requirements, built-up sections may be used. Most commonly used are double angles and double channels placed back to back; cover plates attached to flanges of I-Beam and other similar possibilities.