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Re: Questions about Slab/Column Connection and Detailing (incorrect subject in my previous email)

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Hui,

I agree with what the other engineers said in response
to your question. You can't ignore the moment that
tries to get into the column at the slab/column
joints. 

Ask yourself this: If you "assume" the slab column
joint is a pin connection, don't forget to tell the
concrete that it's a pin and it's not allowed to
resist any moment that tries to get into the joint.

I recently peer reviewed a project designed by another
engineer. I found some punching shear overstresses
(due to gravity loads) at the edge columns. I told the
engineer of these overstresses and suggested that
shear reinforcing or column caps be added at the
joints in question. His response was instead to
re-analyze the slab with pinned joints used in the
computer analysis at the edge columns so that "there
would be no additional shear stresses due to
unbalanced moments at the joint." When I heard that he
did this I told him not to forget to tell the concrete
in the joint that it's a "pin".

Cliff Schwinger

P.S. When you figure out how to tell the concrete that
it's a pin and it's not allowed to grab any moment at
the slab column joint, call me right away and tell me
how you did it. We'll patent your (our) innovation,
make millions of dollars, split the profits 50/50 and
live the rest of our lives in the fast lane (i.e.,
drive cars with less than 100,000 miles on the
odometer). OK?








--- Hui LI <hli(--nospam--at)maengineering.com> wrote:
> Sorry to send this email again.
> 
> List members:
> 
> I am designing a condominium in seismic zone area.
> We are using only the
> ShearWalls as Seismic/Wind resisting system and not
> the columns.
> 
> Questions are:
> 
> 1)Should the Slab/Column connection be designed and
> detailed as a Pinned
> connection without considering the moment
> transferred from slab?
> 
> 2)The pinned connection will minimize the punching
> shear stress. But how to
> detail the column/slab connection as pinned
> condition? some technical paper
> mentions that closely spaced ties can be placed over
> a length equal to one
> and one-half times the larger cross-sectional
> dimension of the column (#3 @
> 3 in.), Is this a common practice? Are there any
> other ways?
> 
> 3)Are the columns to be designed/detailed per ACI
> 2002 Chapter 21,for
> instance rebar splice at midheight of the column?
> 
> Your response is greatly appreciated.
> 
> Hui Li
> Projection Engineer
> 
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