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RE: IBC and Rho factor

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Sorry I didn't respond soon - I've been under the weather and
antibiotics can be a real kick in the butt when you get older. At any
rate, I agree Chuck. I think the measures were intended to offer relief
without complication of legality. In other words, it may be what is
recommended and suggested, but without going through the legislation to
change the law as written, but simply to address what some building
officials assume as reasonable.
The wording of the code does not make this easy to deceipher. The code
does not say that the engineer must use flexible or rigid diaphragm, nor
does it specify that the engineer must consider an envelope solution to
the problem. It does not say that a diaphragm is rigid, only that it is
non-flexible and leaves much to be interpreted and therefore, argued
through potential litigation or out-of-court settlements.
Leaving the decision to the engineer can also allow a professional
opinion that states the diaphragm is rigid and therefore justifies the
design of an open-front or soft-story structure which most of us would
not touch.
I think this was what John Coil attempted to do in the design example he
submitted and which was published in the 1999 Proceedings - the SEAOC
Annual Convention Publication. In this example (and I am operating on my
memory so if anyone remembers this better, please jump in), he used a
multi-story residential apartment building in Los Angeles that was
damaged during the Northridge Earthquake. The occupants of the building
did not want to be disturbed and the retrofit of the perimeter, exterior
piers where shear was originally transmitted, was not allowed in the
building retrofit. 
I recall that he used a spreadsheet developed by Zeb Ficcadentti's
office to calculate the distribution of horizontal shear by rigidity and
he defined only the corridor walls as appropriate shear resisting
elements. The diaphragm was essentially cantilevered over the central
corridor creating a soft-story on at least two sides. 
Computer programs are great tools, but I don't think they should ever
take the place of an engineers judgement and soft-story design by
rotational analysis alone was dropped from the Los Angeles City Building
Code for multi-story wood framed structures (and URM's) after the
Whittier Narrows Earthquake of 1987. As I recall, the City of Los
Angeles passed an emergency Ordinance at that time to disallow any
rotation design for garages that had living units above. 
So where is the logic in Coil's design other than to use the ambiguity
of the wording of the code to allow him to reinstate rotational design
in a multi-story residential building so as to satisfy the boundries set
up by the tenents of the apartment building? Will Nature transfer load
to the locations he or the tenents specify as being convenient to them
or will the building twist and cause more damage? Only the next
earthquake of equal or larger magnitude can tell and then we will also
know if Coil (if he is not retired by then) is sued for his belief.

I'm not trying to trash John Coil - especially if he honestly believes
that he is correct and that his paper represents a significant
demonstration of the best way to solve this problem. I don't agree and
that is my professional opinion.

The arguments that we present here are just that - professional
opinions. The problem is that unless the law (the code) is specific in
its language as to how the engineering community intends for these
buildings to be designed, our attempts to find a reasonable and less
restrictive means to design buildings may just be argued by a convincing
expert witness to the contrary. I still believe strongly that if there
is a building code adopted by the State of California, that unless it
attempts to rewrite and publish its own code, it can not modify the
method of design to yield anything less than equal or greater
restriction.

Dennis

-----Original Message-----
From: chuckuc [mailto:chuckuc(--nospam--at)pacbell.net] 
Sent: Thursday, October 03, 2002 11:35 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: IBC and Rho factor


Dennis-
I believe you are correct. This issue is about to be further clarified,
if & when the Gov. signs SB800. Here is the salient section:

 >(4) A structure shall be constructed so as to materially comply  >with
the design criteria for earthquake and wind load resistance, as  >set
forth in the applicable government building codes, regulations,  >and
ordinances in effect at the time of original construction.  > As I
understand the matter of local code modification, local jurisdictions
may alter the provisions of the State Code by conducting local
legislative hearings that demonstrate that local conditions are
significantly different, and thus require different code provisions.
(local Fire Departments do this regularly around here). The local CBO is
not the Emperor of the North Pole, able to rewrite black letter code at
his own discretion. The local City Council must have hearings & adopt an
amending ordinance in order to change the provisions of the CBC. Chuck
Utzman,P.E.

Structuralist wrote:

 >Ben,
 >Giving this some further thought, I don't believe that engineers are
off  >the hook from potential liablity. Here is my opinion on the
issues.  >  >A building department can adopt and accept anything that
they believe to  >be valid or reasonable for the design of a structure.
They can not,  >however, reliquish the engineer of record from potential
liablity if the  >results of his or her design is less than that which
would be the result  >of compliance to the current code in force - the
97 UBC. The building  >official is not liable - even if he or she
provides the wrong advice to  >the design engineer and the engineer
assumes all responsibility should  >he or she be challenged in court.  >
>If the 2003 IBC is adopted by the state of California and then adopted
>by each jurisdiction, the engineer would be free of liability to
conform  >to the code. However, if the Tri-County and the city of Los
Angeles  >chooses to accept work based on the wording of the 2003 IBC
code and  >even amends a policy in that jurisdiction, the results of the
revised  >code acceptance, but be sure to produce results that are equal
or  >stricter than what is currently adopted in California as the 97 UBC
or  >98 CBC.  >  >Please correct me if I am wrong. The city has decided
to be lenient on  >the issue of design, yet in a courtroom, the engineer
is required to  >design to whichever his the law in the state and the
local jurisdication  >can not adjust the law to something less
restrictive without changing  >the state code or law first.  >  >If
there are any expert witnesses or legal minds out there I would like  >a
ruling on this. I know that our local jurisdiction will require a
>change in the code that is approved first at the state level and not
>simply adopted by any one jurisdiction no matter how powerful it might
>be. If the building official carries no liability, the design engineer
>should be very careful what he or she accepts to be the standard of
>professional practice.  >  >Cautiously,  >Dennis  >  >-----Original
Message-----
 >From: Yousefi, Ben [mailto:Ben.Yousefi(--nospam--at)ci.sj.ca.us]
 >Sent: Wednesday, October 02, 2002 3:21 PM
 >To: 'seaint(--nospam--at)seaint.org'
 >Subject: RE: IBC and Rho factor
 >
 >
 >Dennis, please see my answers below:
 >
 >-----Original Message-----
 >From: Structuralist [mailto:dennis.wish(--nospam--at)verizon.net]
 >Sent: Wednesday, October 02, 2002 2:29 PM
 >To: seaint(--nospam--at)seaint.org
 >Subject: RE: IBC and Rho factor
 >
 >
 >Ben,
 >I'm no longer an SEA member so I won't be receiving the notes from
this  >presentation. What I want to ask is this:  >  >1. The 20%
increase that you are refering to is the difference between
 >2.5Wd/(1.4R) and 3.0Wd/(1.4R) I take it???
 >
 >(BY)Yes
 >
 >2. Don't you require V=3.0Wd/(1.4R) to be multiplied by a Rho of 1.5?
>  >(BY)No  >  >3. Do you consider plywood covered in lightweight
concrete to be  >flexible or rigid?  >
 >(BY) Yes. The concrete topping is not a continuous diaphragm, it is
>discontinued by wall sill plates and there is no documentations that
>proves it causes the plywood to act rigid.  >  >4. Doesn't the code
still require the engineer to calculate the  >deflection of the
diaphragm before assuming it is flexible and using the  >Simplfied
Static Method? This was my interpretation of the code as I  >could not
find any specific wording that stated the engineer may use  >flexible
diaprhagm analysis for a wood structure three stories or less  >based on
Simplified Static proceedures. My interpretation has always  >been that
the engineer must first calculate the diaprhagm deflection. Is  >the
assumption of flexible diaphram only the Tri-County's comprimise on
>the issues?  >
 >(BY) No, if you comply with the simplified method provisions. For all
>other cases you are correct. The new policy (amendment) that I was
>referring to which will be adopted November 1 by most LA and Bay area
>jurisdictions, is modeled after the new language in 2003 IBC and it
>reads as follows:  >
 >"1630.2.3.4	Horizontal Distribution.  Diaphragms constructed of
 >untopped
 >steel decking or wood structural panels or similar light-frame
>construction are permitted to be considered as flexible"  >  >  >
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