QUESTION: (SUMMER2016) For wide-flange sections used for building construction, should I specify CSA G40.21 Grade 350W or ASTM A992?

ANSWER: ASTM A992/992M should be specified. It is the grade that North American wide-flange mills produced to and CSA Standard S16-14 (and S16-09) explicitly recognize. Introduced in the 1990s as a product with enhanced properties for seismic applications, A992 is produced to additional controls for mechanical properties, such as a maximum yield stress limit and a maximum yield-to-tensile strength ratio. ASTM A992/992M steel is also preferred for greatest sourcing flexibility although mills in North America would certify their products destined for Canada to CSA G40.21 350W as well as ASTM A992/A992M.

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.

QUESTION: (SPRING2012) When CSA G40.21 300W steel strip is specified as the material for light braces in a building structure, can commercial grade steel products be used instead? What if they are supplied with a test report showing yield stress values matching or exceeding 300 MPa?

ANSWER: No. The reasons include:

a) Commercial grade steel sheet and strip are not produced to meet mandatory mechanical properties, such as minimum yield point, tensile strength and elongation; and
b) Strength levels reported on mill test certificates should not be used as the basis for design. See Clause 5.1.2 of CSA Standard S16-09.