| Author |
Message |
Jerome J. Lazar, RA, CCS, CSI, SCIP
Senior Member
Username: lazarcitec
Post Number: 220
Registered: 05-2003
| | Posted on Wednesday, May 17, 2006 - 12:17 pm: |    |
Scenario: several elevated decks of a post tensioned concrete PG have recently had severe ponding lasting at least 24 hours. Contractor advises that he built the PG per ACI 117 tolerances, slopes appear to be placed per the drawings and drains are per code. All horizontal concrete has received 2 coats Thompson Waterseal (per Structural Engineer's specifications). Question, other than the issue of the concrete deteriorating from moisture penetrating cracks and corroding the steel prematurely, are there any other issues that the Architect can use to force the contractor into correcting the work at contractor expense? |
Phil Kabza
Senior Member
Username: phil_kabza
Post Number: 170
Registered: 12-2002
| | Posted on Wednesday, May 17, 2006 - 09:26 pm: | |
I don't know if the ponding is so extensive that it keeps the owner from utilizing the facility for its intended purpose, but if the slopes meet the drawing requirements and the structure meets tolerances, I'd have a serious chat with your SE about the slope design in his/her work.
I'd also ask your SE what ASTM standard Thompson Waterseal meets, and why he/she selected that product rather than a commercial specification-grade traffic coating. The Thompson website doesn't appear to have any product data. If it's what I remember it to be, it provides no wear protection to the concrete surface, with the likelihood that water penetration and potential corrosion of post tension strands will result. |
Doug Brinley AIA CSI CDT CCS
Senior Member
Username: dbrinley
Post Number: 223
Registered: 12-2002
| | Posted on Wednesday, May 17, 2006 - 09:45 pm: | |
There are several possible 'vehicles' (bad pun, I know) the architect might employ but please indicate -
1) open, semi-enclosed, or enclosed garage?;
2) severe ponding = standing water (depth?);
3) several elevated decks = how many (three, five, ?)
4) please indicate the "design" slab thickness.
5) drop caps, or no?
I think you've got a different issue. Remember that the Contractor built the forms, and the concrete is where the forms were - at one time. The Contractor didn't lay out the concrete, he laid out the forms. Also, anytime shores are removed from slabs, those 'permanent' elements move. When we have slabs sloping (and not sloping) the way they were designed, it usually means:
1) the formwork was laid out differently in some seemingly minor respect that ultimately affected the design;
2) shores were pulled prematurely;
3) soil density in the area of columns was insufficient and this was not identified previously'
4) contractor work sequences and or staging exceeded soil pressures well recognized by the design team but not well understood by the contractor.
Waterproofing
Thompsons is a dandy product but it's not suited to this sort of application to my knowledge. Depending on how the garage is situated (eg is it beneath an office building; an independent structure; part of a condo; etc) we'd use either a dustproofer/hardener - a crystalline admixture for structural concrete - or an elastomeric coating. |
Mark Gilligan SE, CSI
Senior Member
Username: markgilligan
Post Number: 80
Registered: 05-2005
| | Posted on Thursday, May 18, 2006 - 01:35 am: | |
You need to answer 4 questions.
1-Was the project built in compliance with the Construction Documents? If so the Contractor walks. Is the ponding due to naturally occurring deflection of the slab?
2-Has there been economic loss to the Owner? Without economic loss your claims may be limited.
3-Were the original Construction Documents appropriate for this site? The use of water seal looks questionable.
4-What sort of remedial steps are appropriate? The application of a heavy duty coating may be appropriate. I would investigate products such as Xypex which is not as sensitive to normal wear and tear of the topping. It is likely that this should have been done in the first place and thus the Owners ability to recover costs would be severely limited.
I am curious whether the engineer regularly designs parking garages and what role did the Architect play in this project.
As an aside, if a fully encapsulated PT system was used on this project you are probably not worried about corrosion of the PT tendons. The mild steel could still be a problem. |
Jerome J. Lazar, RA, CCS, CSI, SCIP
Senior Member
Username: lazarcitec
Post Number: 221
Registered: 05-2003
| | Posted on Thursday, May 18, 2006 - 08:45 am: | |
Good or bad our role on the project has been limited during construction. This is a rather old project, having released specifications back in 2002, construction was not started until 2004. Our responsibility to prepare specifications did not include structural, the Structural Engineer, a rather large firm should have known better regarding the specification for the Thompson's Water Seal - agreed this is a Home Depot special that our office would vever specify on a commercial project, the Developer should have spent the money to traffic coat the decks - but this is a Condo project and most Developers in South Florida don't do that, amazingly even the projects on the Beach, barely get treated with a penetrating sealer.
As far as the amount of ponding, up to 1/2-inch in areas from 12x25 to 20 x 30 feet - big enough to cause a concern for the Architect to address the issue. Ponding remains throughout the day - its been monsooning here lately, though a good test for upcoming hurricane season.
We would assume that the PE took into consideration the natural deflection of the slab, that still does not explain such large areas of ponding, we would expect birdbaths, but not lakes. Can't answer for the PE on their experience base for designing Parking Garages, but we asked several other structural engineers in the area whom we trust and who do similar work and they were surprised there was that much ponding on this project.
On several of our projects, if the Developer does not want to spend the dollars to traffic coat complete decks, we at least request perimeters and high traffic areas, sometimes this will stay in the job without getting VE'ed. |
Anonymous
| | Posted on Thursday, May 18, 2006 - 03:57 pm: | |
Jerome,
PT concrete slabs deflect, and this is a fact of life that hits some projects much harder than others. Yours seems to be one that, due to a number of circumstances, highlights this nasty little secret about PT slabs.
I have had to to some very in depth research on this subject recently for two condo projects using PT conc slabs. I doscovered the following that my help you:
1. measured initial deflection is expected with PT slabs - but it is not possible to predict with exact accuracy what this might be. Could be 3/4 inch, could be 2-1/2 inches. structural engineer's experience is KEY.
2. design deflection is not necessarily directly related to measured deflection, and ACI cautions designers NOT to attempt to use design deflection values to prove that measured deflection is excessive.
3. PT conc slab deflection will continue to grow for about one year after the pour. |
Nathan Woods, CCCA
Senior Member
Username: nwoods
Post Number: 92
Registered: 08-2005
| | Posted on Thursday, May 18, 2006 - 04:43 pm: | |
One of the foremost experts in PT slab design and repair is Ken Bondy, SE. If you really are in a pickle, call him up. He is not inexpensive, but you get what you pay for.
http://www.kenbondy.com/professional.htm |
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