QUESTION: (FALL2015) I am involved with the design of an unenclosed industrial structure for which neither the building code nor the bridge code applies. Should I specify notch-tough steel? Are notch-tough W-shapes available? How do I determine the appropriate level of notch-toughness?
ANSWER: Brittle fracture is a complex subject. In order to limit the probability of its occurrence to an acceptable level, one should account for the consequence of failure together with many influential factors as described in Annex L of CSA S16-14. Notch toughness of steel is only one of these factors. Often, fracture control for structures other than buildings and bridges involves identifying the safe options then choosing the most viable solution. Hence the engineer(s) who is responsible for the design, construction specifications and supervision, QA, QC, recommendation for future inspections, etc. is in the best position to make this decision.
With respect to steel grades and their availability, this is the current situation. Although common structural steels, such as CSA G40.21 Types W and A steels generally possess notch toughness that is superior to many steel products used for non-structural applications, they are not produced to meet specific impact testing requirements. Types WT and AT steels are. Purchasers of Types WT and AT steels must also specify the required notch-toughness category that establishes the Charpy V-notch test temperature and energy level. Similarly, purchasers of ASTM steel grades, such as A992, must specify the appropriate test temperature and energy level if they so desire. To our knowledge, a North American mill produces W-sections up to about 440 kg/m to notch-toughness requirements comparable to CSA 350WT Cat. 3. It should be noted that Charpy V-notch test requirements add cost and lead time. Therefore, they should not be specified indiscriminately.