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RE: Steel Yield Strength, A36 vs A 572

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Title: RE: Steel Yield Strength, A36 vs A 572

>Doesn't this create a dangererous situation wherein "yield" occurs much later
>than anticipated?  And are you telling me that my double angle brace might
>experience a rapid failure in an earthquake, as opposed to the elongation I
>would prefer?

Further to Ron Hamburger's post on this subject, I believe the 1997 AISC Seismic Provisions addresses your concerns about the actual yield strength with the factor Ry. For example, see Section 6.2. The expected yield strength is taken as RyFy for any member-strength-driven force requirement. If you design an angle bracing member as A36, Ry =1.5. If you use another grade, like A572 grade 50, Ry=1.1. So essentially, RyFy equals 55 ksi for either grade of steel. These Ry values are based upon the shape production survey results that Ron Hamburger mentioned in his previous post.

In case you don't have it, you can get the 1997 AISC Seismic Provisions here:

    http://www.aisc.org/documents.asp?mode=docdetail&doc=188

and 1999 Seismic Provisions Supplement No 1 here:

    http://www.aisc.org/documents.asp?mode=docdetail&doc=153

As far as the issue of rapid failure vs. elongation, I don't share your concern. In tensile coupon testing, A36 has 20 percent elongation, while A572 grade 50 has 18 percent elongation. I recognize that real shapes do not deform the same as tensile coupons in either steel grade, but the available ductility in either case remains suitable for the application. Each of these and other steel grades approved for seismic construction are listed in Section 6.1 of the AISC Seismic Provisions.

Charlie