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RE: Proportional Limit, A36 Plate

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Title: RE: Proportional Limit, A36 Plate

>Can I count on the *yield* for A36 plate being over 36ksi, or can I assume
>the proportional limit as equal to *yield*?  My only reference leads me to
>suspect that the proportional limit for steel could be as much as 10
>percent below yield.

For the plate thicknesses you are talking about (1/2 in. and less), there will be a tendency toward a yield strength higher than the minimum specified. Thinner plates gets a more rolling than thicker plates When they are produced from the same heat, the chemistry of the heat will be adjusted (with what the mill guys call wonderdust) based upon the thicker stuff so that it meets the specified minimum yield strength. The extra rolling will tend to elevate the yield strength of the thinner stuff. That said, the mill testing is only required to demonstrate Fy >= 36 ksi and you will have no idea whether your thikness is at the top, bottom or middle of the range produced from the heat.

You may be able to use the Ry factor for A36 plate from the AISC Seismic Provisions (Ry = 1.1) to satisfy yourself that the potential variations quoted i your reference between Fy and the theoretical proportional limit will be offset. With the thickness (thinness) of the plates in question, is anything getting anywhere close to yield anyway? If so, will it make any difference if the steel deforms a little to get to the quoted value of Fy? Local steel yielding is usually quite benign as that means the load redistributes and goes somewhere else.