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RE: Re[2]: Hardy Frame, between code changes

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Thanks Bob,
It's this kind of information that is very important for us to make good
engineering judgment. I appreciate the correction.
Sincerely

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: Bob Chittenden [mailto:bchitten(--nospam--at)dsa.ca.gov]
|Sent: Friday, March 27, 1998 1:01 PM
|To: seaoc(--nospam--at)seaoc.org
|Subject: Re[2]: Hardy Frame, between code changes
|
|
|
|
|The 2:1 ratio is not arbitrary - it was established from cyclic
|tests done at
|the University of California Irvine and the University of Idaho.
|Also,APA did
|some preliminary testing - enough to know that the the deflection
|formula in UBC
|Std 23-2 is not applicable to the 3 1/2:1 wall; the deflection
|formula is based
|on a standard ASTM E72 monotonic racking test with a panel aspect
|ratio of 1:1.
|The limits of the 3 1/2:1 panel were extrapolaed far beyond the range of
|applicability of  monotonic racking data and applied to dynamic, cyclic
|behavior. In this case beeter to use the new limits as prudent
|until APA or
|others do extensive cyclic testing  to establish appropriate limits.
|
|______________________________ Reply Separator
|_________________________________
|Subject: RE: Hardy Frame, between code changes
|Author:  <seaoc(--nospam--at)seaoc.org> at net
|Date:    3/27/98 11:18 AM
|
|
|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
||
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