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RE: Building an additional story to an existing hospital

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(I'm assuming from your e-mail address that you are in Canada and NBCC =
Nat'l Bldg Code of Canada)  

If you have read the literature regarding post-mortems for the 1971
Sylmar, 1994 Northridge, and 1995 Kobe earthquakes, you must have
noticed how poorly structures with column ties such as you describe
performed.  If the hospital is located in even a moderately active
seismic region, it could suffer collapse even without the proposed
addition.  Therefore, retrofitting seems to be in order as a first step.
As one of the other respondents suggested, this doesn't have to be such
a disruptive or expensive operation - and they do marvelous work with
fiberglass, carbon fiber, Kevlar, etc wraps these days.

> ----------
> From: 	terrence turner[SMTP:tnturner(--nospam--at)]
> Sent: 	Sunday, June 28, 1998 7:23 AM
> To: 	seaoc(--nospam--at)
> Subject: 	Building an additional storey to an existing hospital
> Hi,
> 	I have a question wrt to building an additional storey to an
> existing
> hospital.  The hospital was built in the early 70's with provisions
> for
> building an additional 6 stories.  It was designed as a ductile moment
> resisting concrete framed structure with a R factor of 4  (state of
> the art
> for the 70's), therebye decreasing the elastic base shear by a
> quarter.  We
> wish to add an additional steel framed storey therebye minimizing the
> the
> seisimic effect of the storey on the original design.  I have analyzed
> the
> original structural dwgs and have found that the original design does
> not
> meet the current code requirements, 1995 NBCC, for even a R factor of
> 2, a
> nominally ductile moment resisting frame.  It is lacking specifically
> seismic hoops with 135 degree bends and closely spaced hoops at
> potential
> plastic hinge locations.  My question is are we obligated to retrofit
> seismically the orginal building before proceeding with our additional
> storey?  We have heard that the design will not proceed if we propose
> an
> expensive and time consuming retrofit of the existing structure.  Also
> the
> zonal velocity ratio for our area is 0.1.