While I share your opinion, let me use your comment to
allow me to open a door to discussion on concepts not
considered in your response-namely damping and extent.
I am no expert on the subject and here is my intuition
1)DAMPING: Even if the soil is liquified, wont damping
turn down oscilations?
2)EXTENT: Next, suppose your metal building and the
piles beneath are only a small fish in deep sea. How
effiective is the presence of this "pile -stiffened
soil" "stiffened" zone affect the response of the
surrounding soil to seismic wave?
--- "Sherman, William" <ShermanWC(--nospam--at)cdm.com> wrote:
> Per UBC, the base of the structure for seismic
> design purposes is "the level
> at which the earthquake motions are considered to be
> imparted to the
> structure or the level at which the structure as a
> dynamic vibrator is
> supported". This still leaves alot up to
> "engineering judgment". Unless the
> soil around the piles is considered to act more like
> a fluid during an
> earthquake (e.g., liquefied soil), I would expect
> there to be lateral load
> effects between the piles and the soil starting
> immediately below the
> concrete foundation level. Thus I would argue that
> the earthquake force
> starts being imparted to the structure at this level
> (although it likely
> wouldn't be fully imparted until the bottom of pile
> is reached).
> A true cantilever structure would have greater
> deflections and would fail if
> excessive deflection occurs. But piles would deflect
> less due to soil
> support and collapse due to excessive deflection is
> not likely.
> > -----Original Message-----
> > From: Kevin Harris
> > Sent: Thursday, July 19, 2001 2:24 PM
> > To: Seaint(--nospam--at)seaint.org
> > Subject: "Cantilevered Column" Structures
> > Greetings
> > I have a question that has been bugging me for
> awhile that I
> > hope someone can give me some guidance on.
> > Here are the facts:
> > 1) A lightweight pre-engineered building (say 20
> psf) bearing
> > on a pile supported mat that supports tanks and
> > (say 500 psf+).
> > 2) UBC seismic zone 3.
> > 3) Point of fixity of piles is 20 ft below grade,
> per geotech.
> > Would this structure have to be considered a
> > column building system" (R=2.2)? I was wondering
> if I would
> > be released from this low R value because the
> structure is
> > essentially just an equipment foundation.
> > Also, if I have to use R=2.2 for the foundation,
> would the
> > light metal building shell have to be designed
> with R=2.2 as
> > well (unless it can be shown to have 10 times the
> > building stiffness)?
> > Thank you for your thoughts.
> > Kevin Harris, P.E.
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