What is the difference between cold-formed and hot-rolled steel design?

Hot-rolled steel profiles (W, HEB, IPE, ISMB, channels) are formed at high temperature and have thick walls. They are designed using codes like AISC 360, NBR 8800 or Eurocode 3. Cold-formed profiles (C, U, Z, hat, stud) are shaped from thin steel sheets at room temperature — walls are typically 1-6 mm thick. Cold-formed design is governed by AISI S100 (USA), NBR 14762 (Brazil) or Eurocode 3 Part 1-3. The key difference is that cold-formed sections are very slender and prone to local buckling, distortional buckling and lateral-torsional buckling, so the design uses effective width methods or direct strength methods to capture these instabilities. Hot-rolled sections are more robust but heavier per unit of strength. Common applications: cold-formed for purlins, girts, residential framing; hot-rolled for main columns, beams, portal frames.