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Re: Column design

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Yeah...but for a column (end/exterior column or interior) "just
supporting a pre-cast beam" will still have the load from the beam applied
eccentrically to the column (unless if is a roof beam-to-column
connection, in which case it could be a concentric load).  And that
eccentric load will result in the moment in the column (not matter what
"load pattern" used for an exterior column but only for "unbalanced" loads
for an interior column).

You could in theory have the beam (exterior) or beams (interior) sit on
the column and then have the next stories column sit on the top of the
beams.  But you would still have some eccentric load cases for the
interior columns.  And detailing such a beast so that the beams can just
sit in bearing, but the column can not translate laterally relative to
beam, is rather tough thing to do.

The real point is that typical reinforced cast in place construction you
design the concrete system as a frame.  This includes exterior columns.
This because typical CIP concrete construction has all the beam to column
joints as continual, integral concrete...and thus, such joints cannot
really behave anywhere close to a pinned connection.


Adrian, MI

On Mon, 19 Dec 2005 ASQENGG2(--nospam--at) wrote:

> As I said you have to detail it properly, make sure negligible moment is
> transferred to the column. You can detail it in such a way that the end of  the
> beam is just bearing on the column. Just think that the end column is just
> supporting a pre-cast beam.
> I can see their argument of using M=wL^2/8 this way. If you have a beam
> being supported by the column and design the beam as simply supported then the
> columns will just act as support to beam reactions.
> If you design the joint to make sure the moment is transferred from beam to
> column then you should design the column for the moment that is being
> transferred.  You only use the ACI provisions for concrete frame if you  design the
> beam and column as frame.  In your case you have a concrete  frame with beams
> and interior columns but hinge at the end columns.
> Moment are not attracted base on the gross area but based on the capacity  of
> the materials as they are being transferred from member to member. Even how
> big your gross area is if your joint is not designed to transferr the  moment
> then the moment will just goes back to the beam.  That's the basic  theory
> behind moment distribution of frames and continuous beams. That's why as  I said
> at the beginning detailing is the key.
> ASQuilalaJr., P.E.
> In a message dated 12/17/05 2:39:06 P.M. Pacific Standard Time,
> ashraf.manjappara(--nospam--at) writes:
> ASQuilala:
> I don't agree with your view and your argument is against ACI 318  S.8.8.1.
> What will happen if we are not designing column for the moment it  attracts
> based on the gross section area?.

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