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RE: 97 ubc (soft story)

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I would suggest that you read Section 5.2.5 of the 1997 NEHRP Recommended
Provisions or Section 1616.6 of the 2000 IBC. On the point in question,
these two documents very clearly indicate that Martin's interpretation is
exactly what the codewriters had in mind.  I grant you that the organization
and wording of Section 1629.8 of the 1997 UBC could be more clear.  That is
why both of the other references (above) include a table that aids
understanding of the intent.

Unfortunately, as has been discussed often on this list, there is no
mechanism to "change" the 1997 UBC short of some dire emergency; it is
essentially a lame duck.

> -----Original Message-----
> From: Swingle, Mark [mailto:Mark.Swingle(--nospam--at)]
> Sent: Friday, January 14, 2000 12:11 PM
> To: 'seaint(--nospam--at)'
> Cc: 'mswingle(--nospam--at)'
> Subject: 97 ubc (soft story)
> Martin,
> Please understand first off that I am not picking on you.  I just
> think this
> thing should be resolved.  I will submit this formally to the
> Seismology FAQ
> list if it still holds water after I get jumped on by the rest of you.
> There appears to be a problem with Section 1629.8.3, Item 3, if
> one assumes
> your (and others') interpretation that the items in 1629.8.3 (where static
> procedure is allowed) take precedence over those in 1629.8.4
> (where dynamic
> procedure is required), in the cases where they overlap.
> My interpretation is that Section 1629.8.4, Items 2 and/or 4,
> would override
> Section 1629.8.3, Item 3, where the two definitions overlap.  You
> and others
> do not agree.
> Section 1629.8.3, Item 3 reads as follows:
> 3.  Irregular structures not more than five stories
>     or 65 feet in height.
> I believe that this should be changed to read as follows:
> 3.  Irregular structures not more than five stories
>     or 65 feet in height, except where Section 1629.8.4,
>     Items 2 or 4, apply.
> This change would simply codify what I already believe to be the intent of
> the code as it stands now.  Similar wording already exists in Section
> 1629.8.3, Item 2.  As it stands now, it is ambiguous at best, and leads to
> several interpretations that I believe are not the intent of the code.
> Let me give an example.  For this example I will use your
> interpretation as
> stated in the first paragraph above.
> Consider a building five stories tall on a soft soil profile, S(F).
> According to 1629.8.4, Item 4, a dynamic analysis is required for both
> regular and irregular structures.  The exception noted in
> 1629.8.3, Item 2,
> ensures that a dynamic analysis is still required even for
> regular buildings
> under 240 ft tall on this soil profile.  However, since according to your
> interpretation 1629.8.3 takes precedence over 1629.8.4, an irregular
> structure ON THE SAME SOIL would only require a static analysis.
> So, in summary,
> A regular, 5-story bldg on soft soil requires a dynamic analysis.
> An IRREGULAR, 5-story bldg on soft soil DOES NOT require a
> dynamic analysis.
> Something seems to be wrong here.
> Mark Swingle, SE
> Oakland, CA
> ---------------------------------------------------
> Martin W. Johnson wrote:
> <<Section 1629.8.1 says that any structure MAY be, and certain structures
> SHALL be, designed using the dynamic procedure. Section 1629.8.2 Lists
> categories of structures which MAY be designed using the static procedure.
> This includes any irregular structure less than 5 stories or 65 feet in
> height.  The word MAY is used because, per section 1629.8.1, the engineer
> has the choice of using either the static or dynamic method.  Section
> 1629.8.3 says that the dynamic procedure SHALL be used for all OTHER
> structures.  This means all structures not meeting the
> limitations set forth
> in Sectioon 1629.8.2 (irregular structures greater than 65 ft etc.).
> <<My interpretation is that the static force method is permitted
> for a soft
> story structure less than 65 ft in height, but a dynamic analysis is also
> permitted, and is perhaps preferred.
> <<I recently had the chore of looking at a 3 story building where
> this same
> thing occurred - the engineer used a steel moment frame at the first floor
> to accomodate a large open lobby, and then used extensive pywood
> shearwalls
> in upper stories where residences were located.  I didn't like it
> but could
> only spell out what the code says.  Because there were also
> lateral offsets
> between the shearwalls and the moment frames I pointed out several code
> sections which had been overlooked in the design, but the soft story was
> basically in
> conformance with the code.
> <<Martin