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RE: Hollowcore Slab Diaphragm Connection Detailing

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I don't think there is a way of avoiding the topping slab.  There will need
to be a mechanism for transferring shear from the diaphragm (planks) to the
LFRS.  The grouting between the planks is good for about 85 psi(?), which
most manufacturers of planks say is typically good.  Depending where the
project is, the topping slab is required to act as the diaphragm, and the HC
planks essentially act as a form.  The one manufacturer that I've worked
with had a City of Los Angeles approval requiring this.  Yes, adding
anything to the planks will almost render the structural strength useless
because there is only about 1 ½" of cover to the strands.


Don't know if I've confused you more, but that's been my experience with


David A. Topete, SE

Structural Engineer



From: Will Blanchard [mailto:will(--nospam--at)] 
Sent: Monday, May 14, 2007 3:51 PM
To: seaint(--nospam--at)
Subject: Hollowcore Slab Diaphragm Connection Detailing


Hello all,


I had a question about detailing a hollowcore slab diaphragm that I was
hoping to get some help with.  I've asked around here, looked through ACI318
and the old PCI manual that we have here and I've yet to find a clear


When you are designing these things for lateral transfer, my understanding
is what typically happens is the contractor grouts the shear key connecting
the HC slabs and the friction occurring between the adjacent panels serves
to transfer the shear through the diaphragm.  According to the
manufacturer's website the detailing is to be in accordance with ACI 318
Section 11.7.


The first calc Vn = AvfFyM references 'shear friction reinforcement' and the
following page 168, Fig R11.7.4 shows a bar at 45 degrees or so across a
'crack' which in this case I assume to be our shear key.  My question is how
exactly does one get a bar into a pre-cast slab with such small clearances?
I don't see how you have the room.  I called the manufacturer to see if they
had a standard detail for this I was given a confused reply of...we often
see details from engineers that call out for this stuff, but it never
happens there is just no room there.  The shear keys are grouted and that's
the end of it...


Does the rebar go IN the grout key, I don't see how that would help
anything...  Do you really need the rebar across the joint to get the
frictional value?


I know about the option of a topping slab, but I was hoping to avoid this as
its just small storage units I am working on.


I'd appreciate any guidance from those familiar with this.




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