Hollow Core Slabs - Outdoor use?

[bridgebuster]

I have a question about hollow core slabs: Can they be used in outdoor applications? There's a disagreement in the office; someone is doing a preliminary design of a railroad platform, using 15" non-prestressed hollow core; someone else said there's a code requirement that prohibits this (but doesn't know what code).

I couldn't find anything. Meanwhile, we use 15" voided slabs for bridges. Perhaps there's a concern with hollow core being exposed to low temperatures but then again the voids in the hollow core could be filled with insulation, which we don't do for bridge applications.

Thank you.

 

[jayrod12]

Around here, there's no strict prohibition. It's ill advised however it is done. The HC suppliers around here indicate that it must be protected from any water intrusion.

 

[bridgebuster]

Thanks jayrod12. BTW, where is around here? The project I mentioned is in NYC.

 

[jayrod12]

Canadian Prairies

 

[bridgebuster]

Thanks

 

[Teguci]

What happens when the precast cracks and allows salty water into the void? For parking garages in the exposed regions (northeast included), hollow core is a strict no.

 

[MotorCity]

Cast in place and precast/hollowcore are both subject to cracking and water intrusion. I would argue that hollowcore is less susceptible because the prestress tends to keep the crack widths smaller.

 

[JAE]

But higher strength tendons will rust at a much faster rate.

Check out Eng-Tips Forum's Policies here:
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[TehMightyEngineer]

You might be able to do it coordinating with the precaster for additional corrosion protection (increased clear cover, corrosion inhibitors, sealants, external membranes, etc.).

Ian Riley, PE, SE
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

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

 

[cooperDBM]

I think the bigger problems with using most hollowcore outdoors in a cold environment is the concrete and the strand cover. Most hollowcore is extruded which makes air entrainment difficult or impossible in the case of dry-cast extrusion. The bottom cover to the strands is usually a function of the bed setup and can't be changed. A non-extruded casting may avoid these issues. Anyway the best answer would come from a precaster.

 

[dik]

hollow core is a strict no

... now you tell me.

I've done three with 12" HC, the oldest being nearly 40 years old... with care, they seem to hold up. The original construction for the Health Science Centre Parkade, in Winnipeg, is the first one.

I did a 5 or 6 storey apartment building down the street about 45 years ago. Conforce did not recommend using 8" HC for balcony slabs; I forwarded the letter to the developer (I agreed with the precaster) but, the developer ignored our advice.

Dik

 

[jayrod12]

the developer ignored our advice

Story of our lives here in the Peg.

 

[dik]

jayrod: our freeze-thaw cycles are it freezes in the fall and thaws in the spring or early summer...

Dik

 

[dik]

But higher strength tendons will rust at a much faster rate.

If subject to corrosion... just have to take care... a bigger problem is the voids filling with water at the ends due to camber, and, freezing and popping the bottom of the cores out.

Dik

 

[hokie66]

I would have thought the Elliot Lake disaster would have given this form of construction a bad smell, at least in Canada.

Note that bridgebuster stated that the preliminary platform design proposed non-prestressed hollow core, which in itself I find unusual.

 

[dik]

The Elliot Lake disaster had nothing to do with the use of HC slabs other than the system was improperly designed. Any building material would likely have failed with the design skills that went into that. Failure was actually caused by corrosion that was brought about by a leaky building envelope... An Architectural failure, not, an Engineering one.

Dik

 

[bridgebuster]

Thanks for the additional replies. Presently, the platform design is conceptual and won't be advanced past a 30% stage - then it's design build. I assume it will have prestressing because the designers want to use 30' long planks in order to reuse the piers. In the end I wouldn't be surprised if it went cast in place because the platform will have a built in snowmelt system.

We've used non-prestressed solid planks on other other railroad platforms but the spans were smaller.

 

[hokie66]

dik,
I have read all about it too. I think there was plenty of blame to go around, architectural, engineering, inspection, and owner. Hollow core slabs with any type bituminous waterproofing would not be my choice.

 

[dik]

Engineering wise, other than the faulty inspections, there was little input. I think the EOR simply stipulated the design loading; there is no indication that he even reviewed the shop drawings for the hollowcore.

Agreed about the bituminous membrane; this would act as a bondbreaker for the composite topping. There is no indication that the engineer reviewed or approved the manner of construction. The composite construction only came about when the HC supplier couldn't make the system work without significant redesign. No indication the EOR was aware of this 'hiccup'. Have misplaced calcs I did on the various parts of the system, but as I recall, at balanced condition, for those spans, without composite construction the capacity was slightly over 50 psf, and with composite construction the capacity with balanced conditions was slightly less than 110 psf., well below spec'd load. There appears to be no involvement by the EOR for this. I'm of the opinion that the job was directed by the Architect who simply used the engineer for the design loading, and, he had no further involvement.

Imspection is another issue... top quality firms did not provide a proper review.

Dik