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Re: SEAOC Design Manual Vol 3 Example 4 design question:

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Let me try to clarify my opinion. The code gives an upper limit for design strength of shear walls in shear. If you had a shear wall with no reinforcement (theoretically), let's say its shear strength would be around 2*sqrt(f'c). By adding steel, you can increase its shear strength. But the code says you can't take a 6" wall and put in #18 bars @ 2" o.c. (even aside from cover and spacing requirements); after a certain amount of shear steel is added, the wall won't behave the way we want it too. It can behave in a brittle manor, ie, you load it to a point and then it explodes, because the failure is due to brittle concrete failure instead of ductile steel yielding. This upper limit is what the 8, or 10*sqrt(f'c) stuff is getting at. You want to make sure the wall you design doesn't have a nominal strength so high that it might behave in a brittle way. So you compare the design strength of the wall (nominal strength) to the upper limit given in the code. In cases where the concrete is confined, its compressive strength goes up, and the upper limit does, too (eg, shear in joints of concrete moment frames).

Jon Brody, C.E.

From: "frp 2000" <frp2000(--nospam--at)>
Reply-To: seaint(--nospam--at)
To: <seaint(--nospam--at)>
Subject: Re: SEAOC Design Manual Vol 3 Example 4 design question:
Date: Thu, 16 Nov 2000 17:23:52 -0800

...and also what strain it corresponds to.....

----- Original Message -----
From: "Jon Brody" <brodyjon(--nospam--at)>
To: <seaint(--nospam--at)>
Sent: Thursday, November 16, 2000 4:33 PM
Subject: Re: SEAOC Design Manual Vol 3 Example 4 design question:

> The code check is written for comparison with the "nominal shear
> which is the definition of "Vn" as defined in the UBC. I think the point
> the provision is to prevent brittle failure caused by failure of the
> concrete in compression (the compression "strut"); it's a yield mode
> so the phi factor isn't considered.  It's limiting the amount of shear
> strength that can be added due to shear steel, not the allowable overall
> shear stress value.
> Jon Brody, C.E.
> Principal
> Jon Brody Consulting Engineers
> 1045 Sansome Street, Suite 200
> San Francisco, CA  94111
> (415) 296-9494
> (415) 296-9499 fax
> >From: "Rodriguez, Marlou" <mrodriguez(--nospam--at)>
> >Reply-To: seaint(--nospam--at)
> >To: 'SEAINT Newslist' <seaint(--nospam--at)>
> >Subject: SEAOC Design Manual Vol 3 Example 4 design question:
> >Date: Thu, 16 Nov 2000 08:50:16 -0800
> >
> >Turning to Page 229 of the Seaoc Design Manual Vol 3, Example 4
> >Concrete Wall".
> >
> >When comparing phi*Vn with the max per UBC 1921.6.5.6  8*Acv*sqrt(f`c),
> >was not applied to the Max allowed.
> >
> >Can someone explain why phi was not applied,
> >
> >Thanks
> >
> >*************************************************************
> >Marlou B. Rodriguez
> >Biggs Cardossa Associates Inc.
> >Structural Engineers
> >1871 The Alameda, Suite 200
> >San Jose, California 95126
> >408-296-5515 Fax 408-296-8114
> >
> >Note:  The opinions that I write are my opinions and
> >are not necessarily the opinions of BCA.
> >*************************************************************
> >
> >
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