From: "Haan, Scott M." <HaanSM(--nospam--at)ci.anchorage.ak.us>
Date: Wed, 21 Mar 2001 11:37:05 -0900
Here is a check for a big opening.
Ao=8*72=576 ft^2 = big opening
r = 1/[1+[Ao/(H*sum(Li)]] ===> F=r/[3-2*r] ===> Co=min[1,F*L/sum(Li)]
r = 1/[1+[576/(8*8]]=.095 ==> F=.095/[3-2*.095]=.0339 ==>
IBC Table 2305.3.7.2 has Co=.33 almost .339
I is my understanding that F modifies the entire wall capacity and Co is
intended to modify the capacity of the full height segments.
Scott M Haan P.E.
Plan Review Engineer
Building Safety Division http://muni.org/building,
Development Services Department,
Municipality of Anchorage
phone: 907-343-8183 fax: 907-249-7399
> -----Original Message-----
> From: David B Merrick [SMTP:mrkgp(--nospam--at)pacbell.net]
> Sent: Wednesday, March 21, 2001 9:19 AM
> To: seaint(--nospam--at)seaint.org
> Subject: Re: Perforated Shearwall Adjustment Factor reference
> Thanks for the response.
> For most large openings, the IBC table 2305.3.7.2 allows more than twice
> capacity that the equation allows.
> The equation could have a value near to that of the IBC table if the
> 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
> 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
> length of the wall? Probably not, because results would greatly defy the
> of physics.
> David Merrick, SE
> "Haan, Scott M." wrote:
> > In a draft 2000 NEHRP commentary, I got ahold of, it indicates the
> > are based on all unusable height being opening and all opening having
> > same height of the maximum opening. Co in the tables is just the minimum
> > 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