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Hollow Core Plank Details

Hollow Core Plank Details

Hollow Core Plank Details

(OP)
We've occasionally used prestressed precast concrete hollow core planks on projects and have always struggled to develop adequate details for the connections between the planks and supporting walls.  

The biggest difficulty comes with using the planks as roof elements with no topping.  Other than embedding steel plates in the planks and bolting clip angles to the walls, we haven't found any details that correctly use reinforcing bars, developed properly, that work.

Are there any resources, websites, etc. that provide details for this?  PCA and PCI don't seem to show a lot of concepts.

I'm developing a large sense of animosity towards planks these days!  Don't care for the product due to the above.

RE: Hollow Core Plank Details

Plant Precast & Prestressed Concrete by Sheppard and Phillips has 1 or 2 untopped rebar details that might help.

RE: Hollow Core Plank Details

The planks we use in this part of the world have a rebate between them which gets filled with concrete. This means you can put a couple of bars in the rebate which then can be tied into the wall.

The other thing that is often done is that the concrete above some of the hollows in the planks gets broken out near the end of the panel so you get a channel to put reinforcement and concrete in. We do this quite often where two planks are meeting end to end and bearing on one wall to tie the two planks together over the wall.

Carl Bauer
www.bauerconsultbotswana.com

RE: Hollow Core Plank Details

Can you send me an e-mail so I have your address?

dikcoates@alpha.to

RE: Hollow Core Plank Details

Thats what I've seen, Carlbauer.  The tops of the hollow parts are broken out at the ends, and then hooked rebars (that hook around rebar in the wall) are grouted into the cores.

RE: Hollow Core Plank Details

(OP)
Thanks for the responses!

I've seen similar details to what pylko and carlbauer described.  Maybe I'm being too particular, but to be honest, none of them, in my humble opinion, satisfy code provisions of ACI.

For example, a hollow core supported by a concrete masonry wall.  The hollow core usually sits about 4 or 5 inches on the 8 in. wall and a vertical bar extends out of the wall, and is bent 90 degrees into the HC.  The bar either aligns with the "rebate" or keyway between the individual planks, or the top part of the plank is chipped away to allow the bar into the core which is fully grouted.

The problem I have with this detail, is that the bar is never developed properly per ACI chapter 12.  If the wall were to be pulled outward, say by lateral wind suction, there is nothing that directly resists this force.  The bar can't do it because it is simply extending vertically out of the top of the wall and doesn't turn into the plank until about 4 to 6 inches above the wall.  This results in a 4 to 6 inch rebar cantilever that really can't resist anything.  The plank friction on the top of the wall can't be included either.

Even with a topping slab, where the bar is turned into concrete above the HC plank, there isn't a direct load path.

The only thing we've come up with is requiring embedded plates to the underside of the plank directly adjacent to the wall.  We then add an angle that is welded to the plate and bolted to the wall, just below the plank.  However, every contractor/owner we've tried this on has complained.

RE: Hollow Core Plank Details

What about running your vertical bars continuous, then use a horiz. bar in the wall (like a bond beam) at the floor height, then 180 degree hook your rebars for the plank around this horizontal bar, grout the whole course solid and the broken cores of the plank?

That probably does not cover your concerns at a roof level, though.

RE: Hollow Core Plank Details

I agree with pylko that if you use a horizontal bar and 180 degree hook bars into the plank rebate and then grout it all up it should provide a perfectly good restraint to the top of the wall.

Carl Bauer
www.bauerconsultbotswana.com

RE: Hollow Core Plank Details

Hi, guys, you think you have problems!

I was engaged by the National Precast Concrete Association of Australia to develop a computer program for precast (pretensioned) prestressed hollow core planks. The whole membership of the Association was available for consultation. Its input was "empirical", i.e. "we have done it like that for years". A perch of 30 mm on an unreinforced ledge of a precast beam was considered adequate for a plank spanning 9 m.

Fortunately, there was one guy who shared my thoughts after I showed him research going back to 1930, and we ended up with a product (called PCP4.EXE) that does away with a lot of the nonsense that has grown "empirically".

Regards to all, Helmut
http://www.engs-comp.com/

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