Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

Re: Column design

[Subject Prev][Subject Next][Thread Prev][Thread Next]
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.  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