QUESTION: (2015) What are the most common grades for structural steel shapes and sections used in building construction?
ANSWER: The main contributing factors are: a) their suitability for the intended applications as recognized by codes and standards, and b) availability. A summary for common structural steel grades used for building construction is shown in the table below:
It should be noted that an A500 HSS is not an exact substitution for its G40.21 350W counterpart having the same nominal size designation, mainly due to the less stringent ASTM A500 under-mass tolerance and, in some cases, lower tensile strength properties.
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: (2014) Are ASTM A1085 products readily available?
ANSWER: ASTM A1085 is a new standard, introduced in 2013. Atlas Tube Canada ULC has started taking orders in 2013. Time will tell if they will be readily available from service centres.
QUESTION: (SUMMER2011) Why have Welded Wide Flange (WWF) shapes been commonly used in Canada?
ANSWER: The introduction of CSA G40.12 in 1964 marked the beginning of an era for Canadian structural steel. This stronger (300 MPa specified yield) steel replaced ASTM A36 (248 MPa yield) steel as the basic grade for wide-flange shapes, etc. Algoma Steel, the Canadian wide-flange mill at that time, did not produce the full range of W-sections. As a result, the welded wide-flange (WWF) sections were introduced as alternatives for heavy rolled sections.As built-up shapes, the WWF cross-sections can be tailored for optimal efficiency; standard beam sections were compact sections or stockier and all columns were Class 3 or stockier. Because the plates were oxy-flame-cut in Algoma’s facility, their WWF sections were also qualified for the most favourable column design curve (of the three SSRC curves), whereas the least favourable curve applied to heavy A36 W-shapes.The above-mentioned advantages, coupled with the higher strength of the 300 MPa steel, had helped WWF sections to remain popular choices for heavy sections until ASTM A992 (345 MPa specified min. yield) emerged as the common North American steel grade for wide flange shapes about a decade ago. Until recently, WWF sections also benefited from the availability of notch-tough steel plates where required, while rolled shapes, supplied to meet certain notch-toughness requirements, were scarce. Rolled W-shapes, up to 440 kg/m in weight and meeting CSA Type T Category 3 notch-toughness requirements, are now available (subject to minimum tonnage order, etc.). All in all, the clear advantages that WWF shapes once offered have dwindled.
QUESTION: (SUMMER2011) Essar Steel Algoma has closed their WWF production facility. What are the steel designer’s choices?
ANSWER: For several years, another source of WWF sections had supplied the market in western Canada. Following Essar Steel Algoma’s exit, a large fabrication facility in eastern Canada has shown interest in WWF production. The future availability of WWF sections, or lack of, will be sorted out in the marketplace. It should be noted that WWF sections are essentially standardized welded built-up H-shapes (see answer to the question below). Hence they can be replaced with custom-designed welded built-up sections.Here are the current choices: a) North American mills produce ASTM A992 rolled W-shapes up to 1,100 mm in depth, and column sections weigh up to 1,086 kg/m. At current exchange rates, they ought to be very competitive; and b) Welded plate girders for sections deeper than 1,100 mm and where the need to camber heavy rolled girders renders them unsuitable.