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RE: Steel Moment Frames in Seismic Zone 0

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>I need a little help here!! ... Where I
>get lost is the R of 3.  I think what you
>are saying is that if the local building
>department allows the use of a R=3 factor
>that you can forgo the backup bar removal,
>notch tough wire, and if by calculation
>the continuity plates, which may be cheaper
>then the other requirements? ....

OK, here goes.

R=3 is the dividing line for steel systems. Below it, you are permitted to
use systems of normal ductility, which are designed to remain nominally
elastic for all forces. The AISC Specification has the appropriate
provisions for this approach. Note that notch toughness in weld metal,
backing bar treatment, and column stiffening requirements do apply in some

If you choose to use an R greater than 3 (or are required to by the
applicable building code), you must use a system that is covered in the AISC
Seismic Provisions. These are systems that get configured with successively
higher levels of inelastic deformation capability. The higher the R, the
higher the capability. Those additional requirements tend to add features
that also add cost.

When permitted, R = 3 systems are generally the least expensive. There is a
potential performance difference that must be a part of that decision, of
course, based upon the owner's needs.

Does that cover it?


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