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RE: Slab/Column Connection and Detailing

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It seems almost dangerous to detail the columns with pins.  What could be
the advantage?  All you will do is reduce the overall redundancy of the
structure.

Even if you detail the reinforcing as a pin, the accumulated gravity load
will most likely mean that the column may never see tension (depends on
building height etc).  Thus moment will be delivered to the column and slab
whether you want it or not.

You should look at the 2005 draft recommendations for slabs not proportioned
to resist lateral load.  It follows the IBC 2003 section 1908.1.6.  This
will govern the balance between column size and slab thickness.

Craig

-----Original Message-----
From: Hui LI [mailto:hli(--nospam--at)maengineering.com] 
Sent: Wednesday, July 28, 2004 2:27 PM
To: seaint(--nospam--at)seaint.org
Subject: Slab/Column Connection and Detailing

Gentlemen,

Thank you for your input and time.

When modeling the whole building, we use pinned at slab/column joints so
that the shear walls will resist all the lateral loads. We agree that the
roof slab should be fixed due to the fact that vertical bars are developed
into the slab but this is not the case for all intermediate levels that is
why we are wondering if pinned connection is advisable in the design of both
PT and conventional slabs. Additionally, construction sequence does not
allow monolithic pouring of columns and slab and sometimes of different
compressive strengths. The program we use considers the drift of the columns
and we use the provisions stated on ACI Section 21.9 "Frame Members not
Proportioned to Resist Forces Induced by Earthquake Motions".
Is it acceptable to assume a reduced stiffness for the column and
complimented by detailing the column connection to the slab with additional,
closely spaced ties to minimized the width of cracks which may develop at
this junction (PTI Design Fundamentals of PT Concrete Floors p.2-15).
Our ultimate goal why we asking these questions is to reduce column sizes or
slab thickness due to punching shear problem. Any suggestions?
Any input will be greatly appreciated.

Hui Li
Project Engineer


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