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RE: Post-tensioned Construction

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I am currently involved with an older unbonded PT parking structure where I
recently discovered 6 tendons out of 6 tendons (yes 100%) of a perimeter
EDGE band (tendons parallel and adjacent to the slab edge) of a 2-way slab
construction joint in a banded tendon design failed due to corrosion. All 6
strands had zero wires remaining across the CJ. No mild steel rebar passed
through the joint either - none was designed, none was placed. No
bottom/positive flexural rebar either. The slab suffered/failed from
localized vertical drop/displacement at the joint of approx 2", and a
midspan flexural deflection of 5+ inches (span/60), but no collapse as such,
probably due to the concrete wedging and hanging-on from transverse uniform
tendons. I add that cars fully occupied the structure at the time.

Pretty damn difficult to fully fail/collapse a PT 2-way slab, except
probably under dynamic loadings, or punching shear type failure.

Since the Miami condo was constructed in 1974 and possibly post-ACI 318-71
it may have complied with minimum code-specified bonded rebar too.

It would be interesting to find out what other observations (other than just
the failed tendons) were evident in the structure (excessive deflection,
very wide cracks etc) for the decision to evacuate.

I wonder if the decision to evacuate was based more upon a "legal decision"
than an engineering one. Condominium associations certainly like to file law
suits, and win them too.


Mark Geoghegan
Honolulu, HAWAII



-----Original Message-----
From: Stuart, Matthew [mailto:mStuart(--nospam--at)schoordepalma.com]
Sent: Tuesday, March 11, 2003 6:40 AM
To: 'seaint(--nospam--at)seaint.org'
Subject: RE: Post-tensioned Construction


I don?t know if it was an over reaction because the article says:

The problem was discovered when workers doing some repairs on the building
noticed weakened tensions among several cables, said Joe Fernandez,
assistant chief of the Miami Fire-Rescue Department. On one floor, six of 10
cables investigated failed.

As I?m sure you know, if this is an unbonded system that means that the P/T
force has been lost along the entire length of strand, this maybe why they
evacuated the entire floor rather than just the area associated with the
failure.


D. Matthew Stuart, P.E., S.E., P.Eng.
Senior Project Manager
Schoor DePalma Engineers and Consultants
200 State Highway Nine
Manalapan, NJ 07726
732-577-9000 (Ext. 1275)
732 -431-9428 (Fax)
mstuart(--nospam--at)schoordepalma.com

-----Original Message-----
From: GSKWY(--nospam--at)aol.com [mailto:GSKWY(--nospam--at)aol.com]
Sent: Tuesday, March 11, 2003 11:01 AM
To: Seaint(--nospam--at)seaint.org
Subject: Post-tensioned Construction

In what seems to be an example of an incredibly irresponsible
recommendation,  a post-tensioned condominium building in Florida was
evacutated because someone felt it was in danger of collapse.

It is not clear at this point who made the recommendation.

Gail S. Kelley

http://www.sun-sentinel.com/news/local/miami/sfl-dcondo06mar06,0,3724248.sto
ry?coll=sfla-news-miami

http://www.naplesnews.com/03/03/florida/d909235a.htm

http://www.orlandosentinel.com/news/local/state/orl-loctower05030503mar05,0,
3831114.story?coll=orl-news-headlines-state

http://www.luxurymiamirealestate.com/listings/featuredareacondo.asp?faid=851


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