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RE: Perforated Shearwall Adjustment Factor reference
[Subject Prev][Subject Next][Thread Prev][Thread Next]- To: "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
- Subject: RE: Perforated Shearwall Adjustment Factor reference
- 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. L=80ft L1=4 ft L2=4 ft H=8 ft %=8/80=10% opening H=H=8' 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 ==> Co=.0339*80/8=.339 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 mailto:haansm(--nospam--at)ci.anchorage.ak.us > -----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 > 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. > >
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