--- title: "Structural steel and its classification" subject: "Design of Steel and Timber Structure" chapter: 1 key: "semester_6/design_of_steel_and_timber_structure:structural-steel-classification" source: https://www.bctengineer.com/q/semester_6/design_of_steel_and_timber_structure/structural-steel-classification site: BCT Engineering --- # Structural steel and its classification Design of Steel and Timber Structure · Chapter 1: Steel Structures and their Analysis and Design - Asked in: 2071 Magh, 6 marks - Video: [Steel Structures Explained (Beginner to Pro Guide)](https://www.youtube.com/watch?v=4X6zV3MVd8o) — Rigid Academy - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/design_of_steel_and_timber_structure/structural-steel-classification - Whole chapter: https://www.bctengineer.com/md/semester_6/design_of_steel_and_timber_structure/chapter-1 ## Question What do you mean by structural steel? Explain classification of structural steel sections. ## Short answer Sections are classifed as hot-rolled (I-beams, channels, angles, tees, flats, tubes), built-up (plate girders, box), cold-formed light gauge (C, Z sections), and by local buckling class (plastic, compact, semi-compact, slender). Grades follow IS 2062 (E250, E350 etc.). ## Answer **Structural steel** is steel (an alloy of iron with 0.15-0.25% carbon, plus manganese, silicon etc.) that is rolled into standard shapes and used to carry loads in buildings, bridges, towers and trusses. It has high strength, ductility and uniform quality, and is covered by IS 2062. #### Classification of structural steel sections A. **Hot-rolled sections (IS 808)** - *I-sections:* ISLB (light beam), ISMB (medium beam), ISWB (wide flange beam), ISHB (H-beam, used mainly as columns), ISSC (column section). - *Channels:* ISLC, ISMC (light and medium channels), ISJC (junior). - *Angles:* ISA with equal and unequal legs. - *Tees:* ISNT (rolled) and ISHT, ISLT (cut from I-sections). - *Flats, plates, bars, tubes:* ISF, plates, round and square bars, circular/rectangular/square hollow sections (IS 1161, IS 4923). B. **Built-up sections:** plate girders, box sections, compound beams (I with cover plates), laced or battened columns, and lattice girders; used when rolled sections are insufficient. C. **Cold-formed (light gauge) sections:** formed from thin sheets (1-6 mm) into C, Z, hat and tubular shapes; used for purlins, sheeting rails and light structures (IS 801). D. **By local-buckling behaviour** (IS 800:2007): plastic, compact, semi-compact and slender sections. E. **By grade:** E250, E350, E410 etc. as per IS 2062. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which section is a heavy column section among the hot-rolled I-sections? A. ISLB B. ISMB C. ISWB D. ISHB Answer: D. ISHB is the heavy beam/column section; ISLB is light, ISMB medium and ISWB wide flange. (Key point: Hot-rolled sections) 2. Why are built-up sections used? A. Because they are cheaper than all rolled sections B. When rolled sections are insufficient for the required strength C. To make cold-formed purlins D. To avoid welding and bolting Answer: B. Plate girders, box sections and laced/battened columns are used when available rolled sections are not enough. (Key point: Built-up sections) 3. What are cold-formed (light gauge) sections? A. Thick plates 20-40 mm hot-rolled B. Cut tees from I-sections C. Thin sheets (1-6 mm) formed into C, Z, hat or tubular shapes used for purlins and light structures D. Built-up plate girders Answer: C. Cold-formed sections are made from thin sheets and used for purlins, sheeting rails and light structures (IS 801). 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