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Re: [SEAOC] Yield strength of structural steel shapes

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On March 23, 1996, Henry Huang wrote:

> It appears that there is a difference of yield strength for structural steel
> (Fy) between Mill Cert and results of lab coupon tests.  Anybody know if
> there are test data showing the relationship between the two?  Which number
> do you suggest for evaluation the capacity of an existing 
 structure? > 
 
 This is a confusing point as some mills utilize a differt proecedure 
for reporting yield strength than do others.  There are two common 
methods, both permissible by ASTM.  One is to report the yeild 
strength.  This is defined as the stress recorded at a specific 
elongation.  The other method is to report the yield point.  This is 
the little peak in the stress strain curve, before the yield plateau, 
which is higher. Also, the mills test their coupons at a very high 
strain rate - resulting in a somewhat elevated reported stress for 
both yield point and yield stress.  If you are using the mill cert 
values, you should ask the mill what practice they follow and what 
they are reporting.  The yield stress, not yield point is the desired 
value.  Also, if the lab pulled the coupon at a slower strain rate, 
this is more applicable to seismic loading conditions.

Note that SAC is attempting to come up with specific recommendations 
for the industry on how to take and report mill cert data as part of 
our phase II effort, currently underway.

Regards,
Ron Hamburger
Project Director for Product Development
SAC Steel Project
Ronald O. Hamburger, SE
Regional Manager
EQE International, Inc.
San Francisco, California
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