Return to index: [Subject] [Thread] [Date] [Author]

Re[2]: Stupid Things I've Seen

[Subject Prev][Subject Next][Thread Prev][Thread Next]
     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 
> encountered
> 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.