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RE: 1920's 9 story concrete frame building

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Jeff:

I've worked on vintage structures with column detailing similar to 
what you have described.  The spiral columns in the lower stories 
should perform fairly well, depending on the splice detail provided 
for the longitudinal reinforcing.  You might also want to consider 
how much cover a square column with a spiral core will lose due to 
spalling during inelastic, cyclic loading.

The columns in the upper stories would almost certainly need some 
form of rehabilitation since they will be very shear critical.  It 
would also be difficult to reduce the drift in the upper stories 
enough to make those columns work.  Your client should expect some 
jacketing or other rehab measure for the upper columns.

The mix design (1:2:4) is volumetric and consists of 1 bag of cement, 
2 cubic feet of sand, and 4 cubic feet of coarse aggregate.  A basic 
flaw in volumetric mix design is that the amount of water is not 
specified so the resulting w/c ratio and corresponding strength is 
not really predictable.  Using typical proportioning guidelines, I 
would expect a 1:2:4 mix to have a compressive strength of about 3500 
psi.  However, I would base my final rehab design of strengths 
obtained from testing.

-Mike


**************************
> From:          "Jeff Smith" <smthengr(--nospam--at)sirius.com>
> To:            <seaint(--nospam--at)seaint.org>
> Subject:       RE: 1920's 9 story concrete frame building
> Date:          Wed, 12 May 1999 06:37:05 -0700
> Importance:    Normal
> Reply-to:      seaint(--nospam--at)seaint.org
> Organization:  http://www.seaint.org

> Well, the client showed up with some plans and to my surprise the first 5-6
> floors have square columns with #3 spiral ties at 1.5 to 3" pitch. The
> vertical reinforcing ranges from 6 3/4" dia. to  10-7/8" dia bars. Above the
> sixth floor there are basically 4 bars with # 2 ties at 10" o.c. Concrete
> was a 1-2-4 mix for the heavy columns (what does that mean again?)I left the
> plans at my office so the details are a bit sketchy. Bob, I am sure you and
> other SEAONC members would recognize the original Engineers, another
> colleague did. Werner (maybe) someone, someone and Russell I believe. Their
> offices were on Pacific. Even though I am amazed with the amount of
> reinforcing, I still would be very nervous in that building,it is very heavy
> with the pan joists. The aspect ratio is closer to 2.5:1 and it is sort of
> "z" shaped in plan. I have a client who is equally concerned about seismic
> safety and the view, meanwhile a frenzy is building and other bidders are
> lining up without any consultant review what so ever. Maybe my client found
> out about the sale too late or maybe the sellers are note allowing enough
> time for buyers review, I am not sure.
> Regards,
> 
> Jeff Smith

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Michael Valley                                   E-mail: mtv(--nospam--at)skilling.com
Skilling Ward Magnusson Barkshire Inc.                  Tel:(206)292-1200
1301 Fifth Ave, #3200,  Seattle  WA 98101-2699          Fax:        -1201