Hollow Core Panels - Silly question 2

[RickyTickyTavi]

I did a parking garage inspection a few weeks ago where in the driving surface in supported with Hollow-core Panels/planks. The garage is 3 storys and incurred a good bit of damage from Hurricane Harvey flood waters.

Nonethless, there were several Hollow-core panels with large longitudinal full length cracks along the bottom of the members. The cracks were faulted and there were already some signs of deflection. I've had some experience with collapsed Hollow-core panels in the past so I recommended shoring the panels to prevent complete failure.

Anyway, the client would like out-right replace the panels and this is where my lack of experience is hurting me. The dimension of the panel are 3'6" wide by 34'-6'' span length (inside to inside) (could be 35 or 36 end to end). Depth the panel I couldn't confirm, but based on the dimensions I took looks to be either 6'' or 8'', with a 2'' or 4'' topping slab.

So here's my silly question: where can I locate the load tables for a 3'-6'' wide panel? Everywhere I look the tables are 4' or 8'. I'm assuming since the load tables are given in PSF, then the width of the panel is far less critical than the length and depth, but I want to make sure before I specify something incorrectly. Is is something I should talk to a manufacturer about?

 

[RickyTickyTavi]

Another question, regarding replacement. Is this one of those things I should just let the contractor worry about and let them select a pre-cast manufacturer.

Just give them the loads, dimensions, and limitations on how to replace the panel?

 

[JedClampett]

I'd call the manufacturer, but if someone put a gun to my head, I'd use the psf value.
As far as a replacement panel, if you give the loads, dimensions and limitations, you'll likely get the right panel. These precast suppliers have had to work with much less.

 

[TehMightyEngineer]

The width of the panel will be less critical assuming similar numbers of strands per unit width were placed in the panel as in a tabulated panel. For precasting a replacement panel you should be able specify the required width and they will adjust their formwork to match. Might raise their cost per panel due to the custom nature but likely not significantly.

I agree with your second approach. I'd specify delegated design requirements (width, span, required loading, topping, other limitations, etc.) and pass it onto the contractor/precaster to finalize the replacement panel design.

Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/

 

[RickyTickyTavi]

Thanks All.

 

[dhengr]

RickyTickyTavi:
42" wide slabs should give you a darn good hint as th who the local supplier of the slabs was. Ask the local suppliers and get the actual supplier involved in the final solution. Aren’t there any original plans and specs. available? Otherwise, I agree with Jed on loads, dimensions and any special limitations. It might be good idea to try to gain a better understanding of what actually caused the cracking, and its affect on the remaining cap’y., and any potential for a fix which avoids replacement.

 

[RickyTickyTavi]

No Original drawings were available. Built in the early 80's during the oil boom. I've got a call with some local manufacturers tomorrow.

As for the cause, this garage has been poorly maintained. A lot of water infiltration unaddressed over the years. I dont believe these failure planes are related to the recent flood waters. My opinion, the failures are likely embedded metal corrosion of the bottom strand.

 

[KootK]

- At those span, I find 6+4 unlikely. I vote for 8+2.

- Baring some serious serendipity, the precaster doing the work probably won't have a 42" extrusion bed. So you may be looking at a solid plank.

- The PSF route seams reasonable to me although, on a unit width basis, using solid plank will cost some capacity.

- As others have suggested, I think that you just need to supply a precaster with some basic performance specifications here. I think that you goal here is to simply, and roughly, replace the flexural capacity per foot or what was removed. Precast decks share load response rather well so you should think of this more like replacing a strip of a slab than, say replacing a few beams.

- In my opinion, the most important thing here is reconstituting the continuity of the slab so that it can share load as originally intended. And this likely comes down to the grout keys where new meets old. I'd be considering:

a) ensuring that grout keys are cast into the replacement planks even though that's a hassle with solid.
b) Clearing out the existing grout key without damaging the plank terribly.
b) Chipping back the topping on the adjacent, existing planks that will remain so that there's access for keyway grouting from the top. Or dream up some fancy way by which it can be done from the bottom.
c) consider a low/zero camber plank so that you get good alignment between new and existing keys. This can usually be done by incorporating some top strand. Additionally, you might specify some temporary propping to get everything aligned prior to key grouting.





I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[dik]

Unless there is a composite topping...34.5' is pushing 8" hollowcore... very close to a balanced load condition. 6" won't work.

Dik

 

[rapt]

Without a composite topping, you are dreaming at 6" and 8" would be very very uncomfortable!

 

[TehMightyEngineer]

Baring some serious serendipity, the precaster doing the work probably won't have a 42" extrusion bed. So you may be looking at a solid plank.

I doubt you'll get solid plank to go that far under vehicle loads without a fight; the self-weight will be prohibitive. If I were casting it I'd see about blocking out part of the extruder, if possible. If that can't be done I'd block out part of the bed and pour it using cast-in tubing rather than an extruder. Or omit prestressing strands on one side and sawcut the 48" plank (assuming the core spacing allows for this to be cut cleanly).

In my opinion, the most important thing here is reconstituting the continuity of the slab so that it can share load as originally intended. And this likely comes down to the grout keys where new meets old

Agreed. Thankfully the topping will also assist somewhat in tying the new to old.

composite topping

Agreed with all these comments. This will be a long span even with a composite topping.

Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/

 

[KootK]

My impression was that this was a group of planks rather than a single plank. If that's the case, I suppose would could just use a few 4' planks and a partial, as you would with any layout that's not modular (all of them as far as I've seen).

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[TehMightyEngineer]

My impression was that this was a group of planks rather than a single plank.

Hmmm, I kind of imagined scattered but you're right that if you can replace a chunk of them then it might work out to have only one or two partial panels. Obviously easier that way, so OP might consider replacing groups of panels even if this results in more panels being removed than is needed strictly for repair concerns.

Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/