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Re: RE: Steel SCBF Yield Lines

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Charlie,

Did you ask this guy why all the stiffeners? I will now leave you alone on this one.

Steve

>>> Charlie Carter <carter(--nospam--at)aiscmail.com> 05/18/00 01:37PM >>>
One additional note on this topic....

I spoke with the engineer on this project, who clarified that the schematic
bracing details shown in the article unintentionally visually distort the
severity of the tilt of the yield line relative to the brace axis. In the
actual connections, the engineer indicates they are much closer to
perpendicular.

Charlie  

-----Original Message-----
From: Charlie Carter 
Sent: Thursday, May 18, 2000 1:24 PM
To: 'seaint(--nospam--at)seaint.org' 
Subject: RE: Steel SCBF Yield Lines


>from David Merrick, SE
>Modern Steel Construction magazine for May 2000
>.... chevron bracing....sketches show yield lines not
>square with the brace. [Shouldn't] the yield line be
>[perpendicular to the axis of the brace]?...

You are correct, David. The yield line for an SCBF gusset is intended to be
perpendicular to the axis of the brace to satisfy the "2t free" dimensional
requirement in the AISC Seismic Provisions Part I Section 13. There has been
a lot of discussion on this topic, particularly because the requirement
drives up the gusset size whenever the brace can't be placed at a 45-degree
angle.

I've seen details that don't satisfy this geometric requirement on several
occasions before. Although the writers of the 1997 AISC Seismic Provisions
had the picture clear in their minds, readers of the resulting document did
not always pick up on the nuance that the yield line should be perpendicular
to the axis of the brace. To explicitly express this aspect of the intent, a
clarification was made in AISC Seismic Provisions Supplement No. 1, which
was published in 1999.

You can download AISC Seismic Provisions Supplement No. 1 here:

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

Charlie