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Re: CONC - Modern concrete frame building -

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In the 80's, all  interior columns were required to check for 3/K times
the frame displacement, where K =0.67 for special moment resisting space
frame.

Nowaday, say 1994 UBC sect. 1921.7.1 refers to as 3 Rw/8 times the frame
displacement.

Juan C. Gray wrote:
> 
> Tom Chiu wrote:
> >
> > Ron Hamburger wrote:
> Please explain what is the 3-delata/K effect.
> 
> Juan C. Gray
> 
> > >
> > > 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.
>