When specifying steel channel sections for a construction or fabrication project, engineers and procurement managers face a fundamental choice between cold-formed C sections (C purlins) and hot-rolled channel sections (U channel or C channel). While both serve as longitudinal structural members, they differ significantly in manufacturing process, dimensional characteristics, mechanical properties, and cost structure. This article examines the key factors that determine which type suits a given application.
Hot-rolled channel steel is produced by passing heated steel billets through a series of rolling stands at temperatures above the recrystallization point (typically 1,100–1,300°C). This process produces a section with tapered inner flange surfaces — approximately 1:6 to 2:12 incline — and a thicker web-to-flange junction. Hot-rolled channel is designated by web height and weight per meter, such as C10 (100 mm) or C20 (200 mm) under Chinese GB/T 706, or by depth and weight in imperial designations (e.g., C8×11.5).
Cold-formed C sections are manufactured at ambient temperature by roll-forming galvanized or black steel strip through a series of progressive rollers. The process produces a section with uniform thickness throughout, sharp internal corners, and parallel flange surfaces. Unlike hot-rolled channel, cold-formed C sections can be produced with stiffening lips on the flange tips, creating a lipped C section (C purlin) that significantly improves local buckling resistance. Standard sizes range from C80×40×15×2.0 mm to C300×80×20×3.0 mm, with thickness from 1.5 mm to 3.0 mm for most building applications.
Hot-rolled channel sections benefit from the residual stress relief and grain refinement that occurs during hot rolling. They offer superior ductility and toughness, making them suitable for dynamic loading conditions, crane runway beams, and heavy structural frameworks where impact resistance matters. The thicker flange-web junction provides a natural fillet radius that reduces stress concentration at connections.
Cold-formed C sections achieve their strength through work hardening during the roll-forming process, which increases yield strength by 15–30% over the base strip material. However, the thin-walled geometry makes them susceptible to local buckling, distortional buckling, and lateral-torsional buckling under compressive loading. The addition of stiffening lips on lipped C sections increases the critical buckling stress by providing edge support to the flange, making lipped C purlins suitable for roof and wall girt applications in pre-engineered steel buildings.
For equivalent section depth, a hot-rolled channel generally offers higher moment capacity about the major axis due to greater flange thickness and web area. However, the cold-formed C section achieves comparable or better performance per unit weight when properly designed with intermediate bracing and stiffening elements.
Cold-formed C sections offer the lowest cost per meter for light-to-medium structural applications, particularly when produced from galvanized coil stock that eliminates the need for post-fabrication corrosion protection. Standard stock lengths are 6 meters, with custom lengths available at minimal extra charge. Lead times are typically shorter than hot-rolled equivalents because roll-forming is a continuous, high-speed process.
Hot-rolled channel is the appropriate specification for: heavy structural frameworks, crane girders, column-to-beam connections, machine bases, and any application requiring reliable performance under impact or fatigue loading. It is also preferred when bolted connections require consistent flange thickness for grip length calculation.
TXD Steel Profile maintains inventory of both hot-rolled channel (U channel per GB/T 706) and cold-formed C sections (including lipped C purlins) to support mixed requirements on construction projects. Standard lengths are 6 m and 12 m for hot-rolled, and 6 m or custom for cold-formed. Technical data sheets with section properties are available on request.
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