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Re: Masonry shear walls - Response Modification factor

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Since ASCE 7-98 is not usually the adopted "code" and is usually in
"force" due to a reference from the adopted model building code, you will
likely need to look at the model building code that refered you to ASCE
7-98 for the seismic design.

As an example, the 2000 IBC does use the terms ordinary, intermediate,
and special reinforced masonry walls in its seismic design section.  Since
the IBC also "has" the material design in it (i.e. the reference to the
MSJC aka ACI 530), it also provides a "definition" of these wall types and
what design requirements from the IBC and the MSJC need to be followed.
For the IBC language, take a look at section 2106.1.1 of the 2000 IBC.

Unfortunately, the MSJC (ACI 530/ASCE 5/TMS 402) does not use this
terminology, but rather just deals with the detailing requirements based
upon the Seismic Performance Category.  The end result is that the wording
in the 2000 IBC is just providing essentially the same thing but using the
terms taken from concrete design (i.e. ordinary, intermediate, special,
etc) to create an equivalent system to concrete design.  From taking a
brief look at the IBC requirements for ordinary, intermediate, and special
reinforced shear walls, it appears that:

An ordinary reinforced shear wall must be designed using the reinforced
masonry provisions of the MSJC (section 2.3) and must follow the detail
requirements of a Seismic Design Catergory C (which is essentially the
same as what is listed in the MSJC under Seismic Performance Category C
[the MSJC was a little behind the nomenclature]).

An intermediate reinforced wall is the same as an ordinary wall except
there is now an additional requirement of a maximum spacing of vertical
reinforcement not to exceed 48 in.

A special reinforced wall must be designed using the reinforced masonry
provisions (as opposed to the unreinforced provisions) of the MSJC
(section 2.3) and must follow the detail requirements of a Seismic Design
Catergory D (which again is the same as Seismic Performance Category D
requirements in the MSJC from a quick look).


Ypsilanti, MI

On Tue, 10 Sep 2002, Alden Manipula, E.I.T. wrote:

> In BOCA-99, table 1610.3.3, they have listed under "Loadbearing wall system" Reinforced masonry shear walls.  But under table of ASCE-7-98 the have listed Special/Intermediate/Ordinary reinforce masonry shear walls.
> Can anyone please explain, or tell me where to find the definitions for, Special/Intermediate/Ordinary reinforced masonry shear walls?

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