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Re: Redundancy Factor

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I can only speculate a response since the questions have been asked of the 
Seismology committee and they have chosen not to respond or to simply say 
that it was in the code and, therefore, we are responsible to have followed 
the provisions.

1. We are liable for not complying with the provisions since 1988. Engineers 
are being taken into court to try and prove that their non-compliance to 
ridigity analysis for wood structures with wood diaprhagms was the standard 
of of professional practice. If you followed a few of the threads, you can 
find where I issued references to text for the UBC that clearly states that 
if the entire community chose not to comply it will not set a standard of 
practice until the law is changed to adopt the less restrictive measure or 
the actions of these engineers are defined in the code or Blue Book as having 
been the "acceptable level of professional practice". This is what I am 
asking the seismology committee to state for all prior codes in the 2000 Blue 
Book. They must define this practice as the acceptable practice to relieve 
engineers of the existing liability.
I am sure that engineers who specialize in Expert witness work will verify 
that this is a real threat in court which can be mitigated by cooperation of 
our policy makers.

2) Why is it suddenly being enforced?  I have a theory that seems reasonable 
but I can't prove it. I believe that SEAOC must meet their objectives listed 
in Vision 2000 which can be found in Appendix B of the 1996 Blue Book. The 
1996 BB states:
"SEAOC's Vision 2000 Committee has defined a framework for development of 
performance-based engineering procedures. ....... It defines 
performance-based engineering in terms of performance levels, seismic hazard 
levels and performance objectives, and provides guidance for the devlelopment 
and incorporation of performance-based engineer guidelines into future 
editions of the Blue Book."

It is my opinion that the Seismology committee has been able to impliment the 
Vision 2000 provisions for known rigid materials like concrete, masonry and 
steel which have been using these provisons for many years. I don't feel that 
they have been able to work out the problems associated with wood and have 
considered residential structures as something that they will "tweak-out" as 
the methods are applied over the next year of so. The professional policy 
makers are comming up with comprimises to define previously unknown or 
unproven design problems like the determination of flexible diaphragms by 
using a mulitplier of 2.5 times the blocked diaphragm results to represent 
flexible deflections. 

Remember that the new code is more extensive inasmuch as it takes into 
consideration proximity to active faults and is affected by varying soil 
conditions. All of these factors have been combined and defined in the new 

The seismology commitee and board members of SEAOC combined with ICBO have 
taken specific measures to endorse the methods despite the problems that 
exist in residential structures.

I believe that this is why our policy makers have taken a stricter line to 
enforce the methodologies. I will satisfy the objectives of a plan that has 
been in the works for a number of years and is finally reaching it's target 
date for full compliance.

The downside - as long as there are unresolved issues with wood framed 
structures, compliance to these methods will create unpredictable results and 
open the design engineer to liability. The liability is automatic as the 
intent of the code is to create predictable performance in wood without 
addressing construction quality problems.

These are my opinions and do reflect the opinions of my employer - me.

Dennis S. Wish PE

In a message dated 8/1/99 5:04:01 PM Pacific Daylight Time, SDGSE(--nospam--at) 

<< Dennis,
 As you and others have put forth the question "what has changed since 1988 
 UBC to require us to do rigidity analysis on wood floor diaphragm now that 
 1997 UBC is in effect?". I still have not seen or heard an answer other than 
 "because it was presented in a seminar as an example." If the code language 
 regarding rigidity analysis has not changed since 1988 UBC, why are we 
 required to do that on residential wood frame diaphragms NOW and not since 
 1988? If we are going to be liable now for not doing rigidity analysis, why 
 aren't we liable for not doing it since 1988, or are we? Some tribute the 
 "change" to the aftermath of Northridge earthquake, but again the 
 was there since 1988. I don't believe there is a specific language in the 
 1997 code that says "the rigidity analysis is now required for wood frame 
 diaphragms as well," so, why consider it now if it was not considered since 
 1988 UBC? If the intent of the 1988 UBC was to require such an analysis on 
 wood frame diaphragms, why wasn't it advertised or didn't it become known 
 then rather than now?
 Any official explanation or an explanation of an Official? Maybe the authors 
 or presenters of the example presented at the wood seminar last year know 
 Oshin Tosounian, S.E. >>