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RE: CONC - Modern concrete frame building -

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As I recall the ductile frame was precast.  It was detailed very nicely and 
performed in an extremely ductile fashion, demonstrating that precast can 
be made to perform well if it is properly detailed.  The problem with the 
structure was that the unplanned load path was stiffer than the planned 
load path and included non-ductile elements whose failure precipitated a 
gravity collapse.  The ductile frame was probably uncracked prior to being 
pulled into the center of the building by the progressive gravity collapse.

-----Original Message-----
From:	Tom Chiu [SMTP:Tomchiu(--nospam--at)worldnet.att.net]
Sent:	Friday, February 27, 1998 7:00 PM
To:	seaoc(--nospam--at)seaoc.org
Subject:	Re: CONC - Modern concrete frame building -

Ron Hamburger wrote:
>
> Tom Chiu wrote:
>
> > I just got an inquiry about damage assessment on "modern concrete frame
> > buildings" after the Northridge earthquake.  The inquiry is that, were
> > there any damage suffered by those concrete frame buildings detailed 
per
> > today's standards, meaning prior to 1994 and say after 1982's 
standards.
> > Since I am also interested in this area as well and the responses may
> > also benefit everyone, I decide to post the question here.
> >
> > I had assessed lots of damaged concrete shear walls, both
> > poured-in-place and tilt-up wall panels with large openings type
> > buildings But I had not seen damage in the MODERN concrete ductile 
frame
> > buildings yet.  Just getting curious to hear from some of you.
>
> The parking garage at Cal State Northridge incorporated a "modern"
> concrete frame structure and also experienced collapse.  The frame
> itself did not collapse.  Failure initiated due to the inability of
> the interior columns (and possibly the diaphragm) to withstand the
> deformations imposed on the structure by the frames' response to the
> ground motion.
>
> - This is probably the single biggest potential cause of poor
> performance of such structures.  Until the 1997 UBC, the code did not
> provide adequate assurance that non-participating elements would be
> protected under the large deformations that a frame could experience.
_______________________________________________________________________
Yes, I forgot about this famous example, Allan Porush of Dames & Moore
was retended by CSUN to investigate this parking structure. I believe
there was also some design faults involved also.  The short ramp walls
between the various levels may have contributed to the collapse, since
those walls were not designed for seismic but were acting as stiff shear
walls.  Precast construction also behaved poorly in seismic event while
the frame itself was really ductile from my recollection of the
pictures.  I doubt that the interior columns were designed for P-delta
or 3-delata/K effects.



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