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Re: 97 ubc (soft story)

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Mark:

I don't believe that there is any "conflict or ambiguity" in this 
case.  As you noted, Section 1629.8.3 (which allows use of the static 
procedure for the structures in question) precedes Section 1629.8.4.  
Please read my emphasized sentence below:
"1629.8.4 Dynamic.  The dynamic lateral-force procedure of Section 
1631 shall be used for all  OTHER structures, including the 
following:"

This section applies to all OTHER structures--that is, those not 
previously defined in Sections 1629.8.2 and 1629.8.3.

Although the code clearly allows the use of the static procedure for 
such low-rise, irregular structures, personally, I would invoke 
Section 1629.8.1 in my design.  In other words, I'd use the dynamic 
procedure.

-Mike

*********
> From:          "Swingle, Mark" <Mark.Swingle(--nospam--at)dgs.ca.gov>
> To:            "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
> Subject:       Re: 97 ubc (soft story)
> Date:          Wed, 12 Jan 2000 13:08:49 -0800
> Thanks for the response.  It seems to me that this is an example of a
> conflict or ambiguity in the code, and that you have chosen one side, while
> I have chosen the other.  1629.8.3 Item 3 and 1629.8.4 Item 2 have an
> overlap in their definitions of building type, and that is where the
> ambiguity lies.
> 
> A building less than 5 stories or 65 feet in height, having a vertical
> irregularity of Type 1, 2, or 3 (Table 16-L), would fall into both
> definitions (1629.8.3 Item 3 and 1629.8.4 Item 2).  Therefore it is up to
> interpretation (rather than clearly stated) as to whether a static or
> dynamic analysis is required for such a building.
> 
> Here is my interpretation:
> 
> Section 1629.8.3 uses the word "may" in the first sentence, however 1629.8.4
> uses the word "shall" in the first sentence.
> 
> Section 1629.8.3 Item 3 applies to ALL irregular structures less than 5
> stories or 65 feet in height, regardless of whether the irregularity is a
> vertical or plan irregularity, and even includes irregularities not defined
> in Table 16-L and 16-M (see 1629.5.3).
> 
> Section 1629.8.4 Item 2 applies only to SPECIFIC types of irregular
> structures, rather than to all irregular structures.
> 
> Considering that the dynamic requirements use the word "shall", and that
> Section 1629.8.4 Item 2 is a SUBSET of the more general definition above it,
> it seems to me that this requirement takes precedence over the other.
> 
> If this were not the intention of the authors, then Section 1629.8.4 Item 2
> would have the further restriction that it applies ONLY to structures
> GREATER than 5 stories or 65 feet in height.  The following paragraph,
> 1629.8.4 Item 3, has such a restriction for clarification.
> 
> Based on the reasons given above (derived only from the language of the
> code), as the code is now written (and has been since the 1988 UBC), it
> seems clear to me that ALL buildings with soft stories, mass irregularities,
> and vertical geometric irregularities (Items 1, 2, and 3 in Table 16-L) are
> required to have a dynamic analysis.
> 
> Mark Swingle, SE
> Oakland, CA
> 
> These are my own opinions.
> 
> PS  Also note that before the 1988 UBC, the only requirement was that the
> dynamic characteristics be "considered" for buildings with structural
> irregularities.
> 
> PPS  Perhaps this is a good candidate for the Seismology FAQ list.
> 
> -----------------------------------------
> 
> On 8 Jan 00, Ben Yousefi wrote :
> 
> <<In a message dated 1/7/2000 4:17:18 PM Pacific Standard Time,
>   Mark.Swingle(--nospam--at)dgs.ca.gov writes:
> 
> <<  << The code DOES allow a soft story.  However, the penalty
>        is severe.  A soft story is a.k.a. a vertical 
>        irregularity of Type 1 (Table 16-L), and you must
>        therefore perform a dynamic analysis per 1629.8.4.   >>
> 
> <<Mark:
> 
> <<This, IMHO, is not completely accurate. Although as a general rule
> table 16-L references section 1629.8.4, Item 2 (Dynamic procedure) for
> structures with stiffness irregularity, Section 1629.8.3, Item 3
> specifically allows the use of static procedure for any irregular
> structure less than 6 stories or 65 ft in height. There may be other
> ramifications for the design based on the type of irregularity,
> but dynamic procedure is not required.
> 
> <<Ben Yousefi, SE
> <<San Jose, CA>>

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