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RE: Hanger reinforcement

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Mr. Kim,

I have been designing precast members now for 6+ years and I typically
follow PCI 6.8.  Chapter 4 of PCI does address corbels however; you ask
so many questions I am not sure what you are really after.  I have seen
several corbels crack immediately after setting of the twin tee's and
have watched a parking deck come down as a result of insufficient hanger
steel.  When designing a corbel I personally design the corbel as a
separate member and then take the eccentricity of the load applied to
the corbel in the design of the piece itself.  If you still have
questions you can contact me, or contact a local precaster and PCI
member and ask for there opinions.

Hope this helps.


Chad Van Kampen P.E.




From: "Wontae Kim" <kimwontae(--nospam--at)email.com>
To: seaint(--nospam--at)seaint.org
Subject: Hanger Reinforcements

Hi!

I have some questions about the hanger reinforcement.
I am reading "Notes on ACI318-02(PCA)..." and "PCI Design Handbook (5th
Ed.)".
Whenever I say 'corbel', it is spot corbel (not continuous ledge) in
spandrel.

I think that Eq (5) page 15-6 of PCA will govern hanger bar quantity 
 in most cases.  (I wonder where this formula comes from.)
 1) This equation does not consider torsion and shear.
 Shouldn't I add this to torsion/shear rebars?
 2) Why doesn't this equation consider the thickness or general shape of
ledge?
 3) Can't I check separation using punching shear concept like Eq (3)?
 4) Can I place rebars according to Eq (4) except W+3a, effective
length?
  (In the precast spandrel, W+3a is approximate 18 in.
   So, can I use Eq (5) for the 18 in at the spot corbel and 
  Eq (4) for the other 3 feet area, if the Double-T has 6 feet stem
spacing?)
 5) Can I still use Eq (5) for the 'unbalanced loads' case like PCI
Figure 4.5.2?

About PCI Eq 4.5.6.
  When I read its reference by Klein G. J., I realized this equation
takes torsion and
 shear into consideration.
 (They say clearly this is not additive to torsion and shear.)
 5) Can I compare this equation with the above Eq (5)?
 Isn't there too much difference?
 6) Can I apply this equation for the spot(button) corbel on the Precast
spandrel?
 I think that 'm' should be adjusted, because the bearing point is not
usually located
 in the middle of (spandrel thickness + corbel thickness) because corbel
and bearing points
 cannot be identical generally.
 7) Can I reduce hanger bars in the middle of spandrel where torsion and
shear are less?

 Canadian PCI design handbook doesn't incorporate PCI Design Handbook
Table 4.5.1.
....

8)Even though corbel is located in the middle of members like column or
wall,
 do I have to check these hanger rebars?
 If there is enough concrete mass to support compression strut of the
corbel,
 I don't think they are required.

In my personal opinion, this separation problem is not that serious.
My company put many rebars around spot corbel for Eq 4.5.6 of PCI.
I am really curious this separation is the 'popular and serious' problem
in the industry.


Best regards,

Wontae Kim
EIT



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