Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

Re: FW: R-values in Seismic Provisions

[Subject Prev][Subject Next][Thread Prev][Thread Next]
The non structural stuff would increase the period of the building, 
but they would tend to degrade rather rapidly, withouth increasing 
loading on the structure.  The principle of elastic vs inelastic 
response is sort of independent (in my mind) to the issue of 
nonstructural elements.


> From:           "Horning, Dick/CVO" <dhorning(--nospam--at)CH2M.com>
> To:             "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
> Subject:        FW: R-values in Seismic Provisions 
> Date sent:      Tue, 15 Sep 1998 09:29:17 -0600
> Send reply to:  seaint(--nospam--at)seaint.org

> Ron, with all due respect from a practitioner to an expert, wouldn't the
> non-structural parts of a typical building (partitions, glazing, etc.) tend
> to reduce the fundamental period rather than increase it?  (At least up to
> the point where they fail).
> 
> > ----------
> > From:     Ron Hamburger[SMTP:roh(--nospam--at)eqe.com]
> > Sent:     Monday, September 14, 1998 6:10 PM
> > To:   seaint(--nospam--at)seaint.org
> > Subject:  Re: R-values in Seismic Provisions 
> > 
> > On Sept. 14 Bill Sherman wrote:
> > 
> > > > An R of 1 would imply an elastic response. < 
> > >  
> > > While I would agree with the above statement, I have heard some speakers
> > on 
> > > seismic design state that an R-value of approximately 2.0 under the 1997
> > UBC 
> > > would relate to a "fully elastic response".  This does not make sense to
> > me
> > >  can anyone explain the basis for this statement? 
> > 
> > There are several bases for such a statement-
> > 
> > 1- The "actual" period of a structure is probably somewhat longer 
> > (maybe by as much as a factor of 2) than that calculated using the 
> > approximate period formulae.  Thus, the simple base shear formula 
> > (absent an R value) could somewhat overstate the response 
> > acceleration.
> > 
> > 2- Most structures incorporate substantial overstrength.  Actual 
> > yield strengths of steel and concrete are somewhat higher than 
> > minimum specified strength.  Capacities of sections calclulated 
> > during design incorproate phi factors - that reduce strength below 
> > actual expected values.  Designs typically are not optimized as much 
> > as possible.  Engineers arbitrarily throw in more beef than the calcs 
> > may demand. 
> > 
> >  The overall effect of this is that most structures will 
> > not actually start to experience signficiant yielding until they see 
> > somewhat higher accelerations than the Z value in the code would 
> > indicate and will not experience full yield until substantially 
> > larger accelerations are experienced.  The factor of 2 probably 
> > overestimates the start of significant yielding but underestimates 
> > full yielding.  It is probably accurate to say that an R of 2 
> > represents "essentially elastic" behavior.
> > Ronald O. Hamburger, SE
> > Regional Manager
> > EQE International, Inc.
> > San Francisco, California
> > 
> > 
> > 
> 
> 
> Ronald O. Hamburger, SE
Regional Manager
EQE International, Inc.
San Francisco, California