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# RE: Drift at top and rotation/curvature

• To: seaint(--nospam--at)seaint.org
• Subject: RE: Drift at top and rotation/curvature
• From: james korff pe pmp <seaoc(--nospam--at)yahoo.com>
• Date: Thu, 29 Jul 1999 13:01:06 -0700 (PDT)

```Good point.

For steel columns the solution may be more straightforward (pun
intended).

We only have to assume the point of rotation, or location of the
plastic hinge.

For concrete, it is a little more complicated - or am I missing the
forest for the trees.

The underlying reason for my question is that some existing buildings,
such as
parking structures, need to have the ends of columns confined so that
they will be able to deflect in a manner compatible with the slab
deflection during the EQ. That is why the plastic hinges must be at the
column ends, and not at the beams.

I am trying to calculate how much confinement is required to meet code
requirements.

Thus, I am trying to correlate the results of a moment curvature
analysis with the required (by code) drift at the top of the columns.

In other words, what I'm looking for is a relationship between
curvature in the plastic hinge, or hinges if there is a point of
inflection, and the code mandated drift of 0.005h.

Could it be that for such a relationship, only empirical results from
testing each individual case will give the answer?

--- Roger Turk <73527.1356(--nospam--at)compuserve.com> wrote:
> Hm-m-m.
>
> Unless I have forgotten something from Theory of Plasticity, rotation
> in a
> plastic hinge is going to continue indefinitely without increase in
> moment
> (until strain hardening range is reached) as long as the moment
> (plastic
> moment) doesn't unload into an elastic state.  (Same as elongation in
> a
> tension member stressed to yield.  Elongation will continue
> indefinitely
> without increase in load until strain hardening range is reached.)
>
> A. Roger Turk, P.E.(Structural)
> Tucson, Arizona
>
>

===
James Korff, PE, PMP
Structural Composite Consultants
985 E. Hillsdale Blvd, Suite 128, Foster City, CA 94404
Phone 650-796-8997 / Fax 650-345-1355

"May the DISPLACEMENT be With You !!"
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