# Re: Perforated Shearwall Adjustment Factor reference

• To: seaint(--nospam--at)seaint.org
• Subject: Re: Perforated Shearwall Adjustment Factor reference
• From: David B Merrick <mrkgp(--nospam--at)pacbell.net>
• Date: Wed, 21 Mar 2001 12:19:09 -0600
```Thanks for the response.

For most large openings, the IBC table 2305.3.7.2 allows more than twice the
capacity that the equation allows.

The equation could have a value near to that of the IBC table if the equation
assumed a shear that is for the wall length, not the sum of the piers. The
equation would have to have a much smaller factor. To adjust for that possible
assumption, the equation would then be.

F=  F*(L/sum(Li))  =  (L/sum(Li))*r/[3-2*r]
where as before r = 1/[1+[Ao/(H*sum(Li)]]

Can anyone verify this?
Could someone mistake the IBC shear to be factored as the force divided by the
length of the wall? Probably not, because results would greatly defy the laws
of physics.

David Merrick, SE
mrkgp(--nospam--at)pacbell.net

"Haan, Scott M." wrote:

> In a draft 2000 NEHRP commentary, I got ahold of, it indicates the tables
> are based on all unusable height being opening and all opening having the
> same height of the maximum opening. Co in the tables is just the minimum of
> 1 or the sheathing capacity ratio F multiplied by the ratio of the total
> length divided by the usable length.
>
> r = 1/[1+[Ao/(H*sum(Li)]]  ===> F=r/[3-2*r]  ===> Co=min[1,F*L/sum(Li)]
>
> H=wall height
> Ao=total opening based on max opening height times the total length of
> unusuable wall and opening
> L=total length
> Li=length of individual usable segment
>
> Try it with the rules above and see if the Co matches the table in the IBC.

```