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7/1/2005
You should get the 8th edition of the Handbook by the way, not that it would matter very much in this case, as the historical listing is also on page 6-5. Back to your question. According to CSA G40.12, 1971 edition, the specified minimum yield strength ranged from 44 ksi to as low as 36 ksi, depending on thicknesses.
Plates / bars
Up to 1 ½" -- Fy = 44 ksi (not coiled*)
1 ½" - 2 ½" – 40 ksi
2 ½" - 4" – 36 ksi
* if coiled, reduce the yield strength to 40 ksi
Shapes
All shapes were 44 ksi except
12x12 120-190 ft weight -- 40 ksi
all 14x16 - 40 ksi
Angles over ¾" thick -- 40 ksi
The reason for this reduction is that it was not economically viable to guarantee Fy of 44 ksi for larger thicknesses using the thermal and mechanial processes of that period. This is no longer a problem today.
You should note that at that time, the US mills produced mainly ASTM A36 steel, i.e. 36 ksi steel. There were no reductions according to thickness because it was possible to obtain that strength, even for larger thicknesses (given that the yield strength was already low).
During the course of CISC's history, the elastic limit of your everyday steel has increased by more than 50%, from 210 MPa (30 ksi), as listed in S39 (1935), to 350 MPa (50 ksi) as listed in G40.21. We now have 7 types of steel: W, WT, R, A, AT, Q and QT steel. W stands for Weldable, T for Notch-Touch, R for Atmospheric Corrosion-Resistant, A for Atmospheric Corrosion-Resistant Weldable, Q for Quenched and Tempered Low Alloy Steel Plate. Phew. And let's not forget the new kid on the international block – high-performance steel (460 to 480 MPa), which is finding its way in many bridge applications around the world. There will be an IABSE publication on this subject later in 2005.
This question appeared in the "Ask Dr. Sylvie" column of Advantage Steel no. 23, Summer 2005.
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