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Re: Column design

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>>> ASQENGG2(--nospam--at)aol.com 12/20/2005 1:42 PM >>>
 
The issue is not the eccentricity of loadings, the column has to be 
designed 
with the moment due to eccentricity no matter what. The issue is the 
ability 
of the column to attract moment from the beam base on the gross 
sections 
between the beam and column. 
 
The fact of the matter is most of the Middle East use the same short
cut  
calculations and is being accepted. It is similar to accepting
conventional  
framing in wood construction even though if you follow the regular code
for wood  
most of shear wall won't pass.  The acceptance such practice is the
fact  that 
when the steel yield and develop a hinge in the joint then the beam is 
still 
capable of supporting the vertical load being design for  M=wL^2/8.  


But at what cost? Huge deformation (serviceability issue). You do not
expect mechanism to form at service loads, may be for slabs (-->Yield
Line Method), but not possibly for beams.
Never heard of that under service load cases, except the limited
redistribution of negative moments allowed by ACI. Is not the philosophy
of ACI to use elastic method for analyis and strength (inelastic) method
for design? [Sounds incompatible, however]

Suresh Acharya, S.E.



And so 
the practice has been done for many many years and if a  new engineer
trying to 
be smarter than the rest of the region I think  it is being bit too
cocky.  
When in Rome do what the Romans do.
 
Another example are the old houses that use 2x4 rafters.  If you 
calculate 
base on the present code, then the 2x4s won't pass.  Some  engineers
think that 
the rafters held up for many years due somewhat effect of  roof
sheathing 
acting as shell.  Some attributed it to some degree of  redunduncy. 
 
 
 
In a message dated 12/19/05 4:39:44 P.M. Pacific Standard Time,  
smaxwell(--nospam--at)engin.umich.edu writes:

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.

Regards,

Scott
Adrian,  MI






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