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RE: Dual System-Shearwall Boundary Element as Column for Conc Mom ent Frame?

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Title: RE: Dual System-Shearwall Boundary Element as Column for Conc Moment Frame?

What you are talking about is not a true dual system.  The concept of a dual system is that the walls or braced frames accumulate curvature from lateral forces as you go up the building thus becoming less stiff the higher you go and the moment frames have relative constant floor-to-floor stiffness up the height of the building. The shear walls  resist most of the shear through the height of the building but the moment frames get most of it in the top couple of stories and transfer it back below that. The overall effect is that the building is much stiffer because moment frames resist some of the drift from curvature that would occur in the upper stories if the system had walls only.

The system you are describing is more like an outrigger braced hybrid coupled wall structure with a coupling beam that transmits overturning forces to the outer column or pier.

-----Original Message-----
From: John Diebold [mailto:Jdiebold(--nospam--at)]
Sent: Tuesday, October 01, 2002 9:27 AM
To: seaint(--nospam--at)
Subject: Dual System-Shearwall Boundary Element as Column for Conc
Moment Frame?

Can a dual system shearwall with concrete moment frame have the shearwall in line with the moment frame such that the end column of the moment frame is also the boundary element of the shear wall? If so, how would this be distinguished from a shearwall-frame interaction system? Is the only difference the amount of seismic load that the moment frame can resist(i.e. 25%)? (Zone 4)

SEAOC's 1999 Blue Book indicates in the commentary on Dual Systems: C104.6.5.2 and C104.6.5.3, Item 2 "...Columns of the frame system may also function as boundary elements of shear walls. As such, these columns must be designed to resist the vertical forces resulting from overturning moment in the shear wall along with the load effects associated with the frame system." The commentary, however, does not distinguish whether the boundary element (when permitted to be used as part of the moment frame) has the moment frame perpendicular to the axis of the shearwall or whether it could be in line with the shearwall.

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