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9/5/1995
It depends. For small jobs, Class C should be specified. For larger jobs, if the higher compressive strength available with Class H can be used effectively, it may be suitable. Designers should check with a local CISC Member Fabricator before making a decision to specify Class H sections.
Class H sections are either hot-formed to final shape, or cold-formed to final shape and then stress-relieved. Class C sections are cold formed and are not stress relieved. Thus, due to the difference in methods of manufacture, Class H sections have a more favourable residual stress pattern. Accordingly, Class H sections can be designed for a larger axial compressive resistance than Class C sections, in accordance with Clause 13.3.1 of CAN/CSA S16.1-94 "Limit States Design of Steel Structures".
Class C sections are the sections normally available in stock, in steel service centres, for example. Class H sections usually require a special mill order, and are more expensive than Class C sections. Thus, if the tonnage of a single size of HSS is large enough to justify a mill order directly from the manufacturer, and the increase in strength offsets a higher cost of material, Class H sections may be the preferred alternative. Otherwise, Class C sections are likely to be a more suitable choice.
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