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RE: Dual System?

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Kenny:


For both questions:  You have got to read 1629.6.5.  1629.6.5 says that a
dual system needs to have a complete space frame that provides support for
gravity loads.  If any of the walls are bearing then the building has to use
a bearing wall system R in both directions per 1630.4.4 and 1630.4.3.

Q1. N & S walls -- EBF frames; W wall -- steel SMRF; E wall -- 
concrete shear wall.  Is this building qualified for a dual system 
building? If not, should R = 4.5 be used in both directions when 
calculating seismic base shear?

N-S is not a dual system if there is only a EBF per Table 16-N item 4. E-W
could have a dual system if the concrete wall is not a bearing wall and the
SMRF is designed for 25% of the base shear minimum per 1629.6.5.

Q2. N & S walls -- EBF frames; W & E walls -- steel SMRF.  If this 
building qualified for a dual system building? If not, should R = 7 be 
used in the W-E direction and R = 8.5 in the N-S direction? Or just 
use R = 7 in both directions?

Not dual system either direction per Table 16-N item 4.  Can use different R
each direction per 1630.4.3 unless you have a bearing wall system in either
direction.  


Grew up on Lake Whatcom.  It used to have awesome cutthroat trout fishing
but the state ruined it by transplanting smallmouths that you can't eat
because they are polluted with mercury.  Great place to  live other than
that though.


Respectfully,

Scott M Haan P.E.
Plan Review Engineer
Building Safety Division 
Development Services Department
Municipality of Anchorage
http://www.muni.org/building
phone:907-343-8183  
fax:907-249-7399
mailto:haansm(--nospam--at)ci.anchorage.ak.us



-----Original Message-----
From: Kenny Yip [mailto:kyip(--nospam--at)anvilcorp.com]
Sent: Tuesday, October 02, 2001 2:05 PM
To: seaint(--nospam--at)seaint.org
Subject: Dual System?


Dear fellows, I need some help with the following two questions.
According to Table 16-N of 97UBC, a dual system can consists of 
concrete shear walls and steel SMRF. 
Q1. N & S walls -- EBF frames; W wall -- steel SMRF; E wall -- 
concrete shear wall.  Is this building qualified for a dual system 
building? If not, should R = 4.5 be used in both directions when 
calculating seismic base shear?
Q2. N & S walls -- EBF frames; W & E walls -- steel SMRF.  If this 
building qualified for a dual system building? If not, should R = 7 be 
used in the W-E direction and R = 8.5 in the N-S direction? Or just 
use R = 7 in both directions?

Kenny Yip
Anvil Corporation
Bellingham, WA


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