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RE: Hardy Frame, between code changes

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Design is based upon Engineering Judgement as much as it is based upon
minimum standards established in code. The engineer should be hired for his
experience and judgment not his fee.
I do not know of too many lawsuits that have been won one the charge of
over-designing. However, I know of many that were won when damaged occurred
from an insufficient design.
I am not entirely in agreement with Bruce since I believe that the public is
being penalized for poor construction practices in the past. The majority of
failures that I explored after Northridge were not due to improper design or
insufficient H/b ratio of shear panels. I discovered that the panel
connection to the studs, the uplift restraint attachment at the studs and
anchorbolt placement were more the cause due to improper installation.
I'd like to ask a question. I am under the impression that the H/b
requirement is required only where the design engineer does not desire to
perform a lateral drift analysis. All minimum standards in the code,
including unsupported plate heights, web crippling (for a few examples) are
established unless they can be proven otherwise by analysis.
If the engineer can determine that a 3.5:1 ratio deflects less than 0.005h
and can provide sufficient restraint for the wall, the issue of an H/b
equivalent to 2:1 is moot.
I have not chosen to design based upon the 1997 UBC simply because it is not
yet adopted. If what Bruce feels should be mandatory practice based upon
good engineering judgement, the Building officials as well as the EOR would
be liable for not adopting a more restrictive measure before it's compliance
date.
Good engineering judgement can also disagree with he provisions of a code -
which in this case my judgement is not yet made.
I believe that with the adoption of Structural Observation requirements
within the City of Los Angeles (and most other places), we should see better
performance on panels that are designed by past code slender ratio's. Just
because the code says it should be this way is not enough. If testing proves
(and it has) otherwise, then I'm inclined to accept empirical data over
subjective writing. I say this because the 2:1 limit started as an emergency
measure shortly after Northridge and has never been reduced in Los Angeles.
I don't feel it was based on any rational test data.
The Blue Book indicates in section C802.2.4 of the commentary that the APA
had not planned Cyclic retesting of plywood shearwalls until some time in
late 1996. This means that the 1997 UBC requirement was passed prior to
testing. Section C802.1.2 states "The height-to-width ratios indicated in
Figures C802-8 and C802-9 are ANTICIPATED for the calculation of
height-to-width ratios.

I believe that Bruce is jumping the gun on this one, but I would never fault
his judgment and this is the essence of good engineering.

Dennis Wish PE
La Quinta, California
wish(--nospam--at)cwia.com
ICQ# 6110557
http://wwp.mirabilis.com/6110557

"Silence is the virtue of fools."
Francis Bacon

|-----Original Message-----
|From: T [mailto:vicpeng(--nospam--at)vtcg.com]
|Sent: Friday, March 27, 1998 9:02 AM
|To: seaoc(--nospam--at)seaoc.org
|Subject: Re: Hardy Frame, between code changes
|
|
|Subject: Re: Hardy Frame, between code changes
|
|
|As a
|>professional licensed engineer, you have a responsibility to design to
|>incorporate the best available thinking into your design not just blindly
|>finally the letter of the Code book.  Particularly in
|circumstances following
|>a "learning experience" such as an earthquake, are we bound to
|wait for code
|>changes to be written and adopted before we try to pass on our
|experience into
|
|
|Do you not have the conundrum that existing legal proscription may
|weigh against you if you use parameters that are not "legal" at
|time of use?  I.e. even if new thinking is "superior" I wonder if
|you don't have the potential for a case against you for using
|parameters not yet "legal", especially if it results in:  a) a
|more expensive structure or b) the new thinking fails in an event.
|
|Thor Tandy  P.Eng,  MCSCE
|Victoria BC
|
|
|
|