None of responses included any post-tensioning (PT) applications. So
here's one that does...
I worked for a PT specialty company once. We were supplying PT along
with shop drawings for a 'big-time' parking garage designed by a
'big-time' Eng. firm. It was a beam / slab system with, mostly, all
standard 25'X60' bays. All the construction was done according to the
'approved' shop drawings - so basically atleast 4 sets of eyes have
looked at them before const., not including GC, CM and the placer.
Almost 70% of the structure was completed. Eng. of record had asked GC
to demolish one of the pours of the slab because of severe
honey-combing in concrete. It was the demolition contractor who called
me with a huge mis-match of demolition strain energy (calculated from
field specific numbers) and actual capacity of the members (calculated
from contract structural drawings), the former being about 30% less
than the latter. He simply asked me if the engr. had allowed us to do
some value eng. on the project. I stalled him off and took a closer
look at the shop drawings to find that all 0.6" PT strands (that I
used in our calculations) were replaced with 0.5" strands (in the list
of materials). Obviously the structure was about 30 to 40% less
stronger than it would've been with 0.6" strands (in one direction -
beams were OK). I knew the slab was over designed, but that did not
stop the chill in my spine. I did a design check with the existing
conditions and satisfied myself that all the code requirements are
met. Since it was a 'combined error' of Engr. / Sub-contractor (shop
drawings were approved by engr.), Engr. took a deep breath and looked
at my calculations and we spent a couple of days setting it right. If
it was not OK - OH! I don't even want to think about it....
Krishna Sandepudi, Ph.D., P.E.
______________________________ Reply Separator _________________________________
Subject: RE: Stupid Things I've Seen
Author: seaint(--nospam--at)seaint.org at NetTalk
Date: 6/29/99 9:00 AM
Most of the responses have had to do with Contractor errors - here is one
where the engineers erred:
When working for a previous employer, I was asked to investigate a design
developed in our office for a steel support for a large heavy steel spillway
gate at a hydroelectric project. Personnel in the field had complained that
one steel column always "creaked" when it was loaded by the weight of the
steel gate. We had a copy of the original design calculations, which had
been checked by a second engineer in the office. The column had been
designed using the assumption that the base of the column was "fixed", but
the detailing of the column base only had two anchor bolts located on the
centroid of the column section. No design of the base plate had been
performed to justify the fixed-end condition. The column was thus
underdesigned due to the erroneous end fixity assumption. We were able to
brace the column before a catastrophic failure occurred.
What I found most amazing was that two separate engineers had been involved
in the design but neither recognized that their design assumptions and
construction details did not match. I am a strong advocate of having
structural calculations checked - but it is scary when even checked
calculations are wrong.
> From: Jim Kestner [mailto:jkestner(--nospam--at)somervilleinc.com]
> Subject: Stupid Things I've Seen
> I think it might be interesting ( and educational) to share
> some horror
> stories of things we have seen. These can be things we have
> in the field or in the office. They may have been done by Contractors,
> Architects, Engineers or even ourselves.
> Please keep them short and avoid using names.