Precast Concrete Double Tee Joists in Parking Garage

[AvengerMolly]

Hi -- I recently did an inspection of a parking garage in Jacksonville, Florida. These cracks in the underside of the precast double tee's were seen fairly frequently. In some cases you can see what looks like rebar peeking through. No cracks were seen on the topside in the middle of the span which did not have a topping. There are visible stitch plates. Almost all exposed rebar and cracks on the top deck were at the edges where it appears concrete was placed on site with poor cover and curing process. There was no recorded rain fall in the 48 hours before my visit and the weather was in the high 80s (I felt it!).

I am a Newby when it comes to inspections (our company does more consulting, drafting, design than inspections). I have done a good bit of research on the causes of cracks in concrete, but I was hoping to get some additional direction and thoughts here particularly as it relates to precast and cast-in-place concrete parking garages.

PS: If you do a lot of inspections, how to you keep track of your photos and notes to put together your final inspection report? Is there a good software for this? My phone takes great pictures and I noted frequently on a printed floor plan for each level... but now I am sitting at my office writing a report and it's so much to comb through and compile (500 pictures, at least 3 dozen areas of exposed rebar/spalling/etc.). I feel like there could/should be a better way. I marked up most of the spots using CAD.

 

[kostast88]

Ribbed slabs are precast. Insufficient curing is not impossible but sounds unlikely, they're made in a factory.

Insufficient cover might be the culprit, although in garages this type of corrosion appears sooner or later even with proper cover.

Carbonation of concrete reduces protection of rebar due to loss of alkalinity (Link). Other factors too. Everytime it rains, concrete is soaked.

Spalling at joints it's quite common, either traffic loads or joint stresses, or both.

To be honest it doesn't look that bad, I'd say small - moderate damage. The problem is there, but is probably at early stages. Wouldn't be able to know how corroded is the rebar inside without a proper survey (half-cell?).

Tip: Don't take TOO many photos on site. Note them down immediately. Mark photo direction with an arrow. Keep it simple. Use a tablet, easier to carry around.

 

[AvengerMolly]

Thank you for the feedback!

Yes, I was thinking curing issues, but like you said... precast.

I didn't think anything was major here either.

Thanks for the tip! I definitely overdo the photos. I basically take photos throughout my walkthrough and have arrows on my drawing to remember the direction I walked in. Because there was so much, I started taking photos of each location when I should have just marked it down and moved on.

Definitely going to use a tablet next time so that I can zoom in and out on the plans too. I didn't do it this time because I'm not as quick on it as pen and paper. Guess I'm an old-school millennial.
I love the idea of marking the photos and direction taken! We live and we learn!

- Molly Richardson, EIT (awaiting PE licensure)

“The Enemy of the best is the good. If you’re always settling with what’s good, you’ll never be the best.“ --Jerry Rice

 

[hokie66]

No real advice on documenting inspections, but I do hate this type of parking structure. There have just been too many collapses for me to feel comfortable about using them. But the big problems are at the connections, not in the individual members.

 

[dik]

The longitudinal crack is at mid span and is likely flexural; it doesn't look too bad, but over time this may change. The transverse cracks are likely flexural, too, but caused by the pretensioning strand putting the top fibres in tension. Parkades are likely designed for a LL = 50 psf and during a large part of their lifetime, may not have any load at all. This is particularly noticeable for long spans. Parkade double tees often have a span in excess of 50'.

I generally take lots of photos and file them in the project file under directory 'Photos'. Just a caution, at one company I worked for, the IT department automatically reduced photos to a minimum size. If these are ever required for court issues, they are likely rendered inadmissable. I always used to create a project CD/DVD with all the photos... good and bad; they were consecutive. I'd date and sign the CD/DVD and file. When doing reports, I'd include a few good and representative photos and note this in the report and that the other photos would be made available, if needed/wanted. I forgot to add, that I generally use a 'real' camera, not a cell phone. Cell phones are pretty good, but generally a real camera is better. My current is a Sony Alpha 6000 that I use on site; is use the brother, the 6400, for off-site. I also have a bag of 'things' to use on site: vernier calipres, measuring tapes, plastic sample bags, pocket microscope, small level, etc.

Same with draft reports; once the final report was done, I'd destroy all previoius drafts. That way I would not have to explain any revisions. I would not keep my drafts on the company system, always on my laptop. IT wasn't happy with my approach.

Corrosion is another item that has to be carefully reviewed and with parkades, even repair can be an issue (see halo effects).

Another small item is that I never did any 'inspections'; they are always 'reviews'. Things were never 'approved' but reviewed with or without exceptions.

Ron can probably add a couple of more things... welcome to a possible future in forensics.

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[KootK]

I'm for insufficient cover. think we might be seeing welded wire fabric showing through on the bottom? If so, that does not portend well for the transverse flexural capacity of the flanges.

Somethings that make me doubt the mesh guesss:

1) I'd expect the tighter wire spacing to run the other way.

2) I'd not expect to see so much curvature along the wires.

 

[dold]

@KootK

If I had to guess, I'd say those "snake" marks on the bottom of the member might be mesh/rebar supports? They look ~2ft o.c.? Not sure why they're all snakey though. Even still, I'd only expect to see the "feet" of the supports, and not the "conduit" looking patter as well.

 

[KootK]

Good call dold.

Even still, I'd only expect to see the "feet" of the supports, and not the "conduit" looking patter as well.

Upside-down?? Musta been training a rookie at the plant that day.

 

[hokie66]

Yes, those are slab bolster marks, so not of concern. And the transverse cracks are restraint shrinkage cracks. The ribs don't shrink as much as the thin slab. The longitudinal cracks are flexural. I don't see any indication of corrosion in those photos, but the whole thing is exposed, so in the future...

Again, pay attention to connections to the supports. And study previous parking structure collapses in Jacksonville and Atlanta, some of which have been discussed on this site. Nasty.

 

[Ingenuity]

I have another “theory” on the soffit snake marks.

These look like cracks that have been epoxy injected where the technician used 1/4” wide tape as a injection port, and cap sealed between the tape, upon curing the tape was removed and the crack injected. Successive “ports” were sealed with wax, upon which the cap seal was removed after the injected resin cured.