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Re: sap2000-nonlinear dynamic analysis

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The nonlinear time history analysis abilities of SAP2000 is very limited,
in my opinion.  Can you do a nonlinear time history analysis using SAP2000
Nonlinear?  Yes you can, but the only elements that are going to behave
nonlinearly are the NL-Link elements.  NL-Link elements are different from
linear elements or linear elements with non linear hinges.  NL-Links must
be drawn independently from the rest of the model and thus, they can not be
"assigned" to an existing element.  (They are drawn using the Draw menu and
Draw NL-Link Element.)  Note that NL-Links must be one of the 6 types
available.  Those types are Damper, Gap, Hook, Plastic1, Isolator1, and
Isolator2.  These few types severely restrict what you can model and what
you can't.  Basically, in my opinion, SAP2000 Nonlinear should only be used
for a nonlinear time history analysis if you are positive that the only
part of the building that will behave non-linearly is the base isolation
system.  (The NLLink elements will adequately model a base isolation
system, but I would not use them for anything else.)  Otherwise, you need
to change software.

There are several different programs you could use.  DRAIN has been the
most commonly used program in the past, but it is very hard to use and the
output is difficult to interpret without a post-processor (such as NONLIN
Pro).  If you can afford it, I would look into RAM's new analysis program
"Perform".  Currently, it is only available in 2-d, but my experience has
been positive (so far).  I would also recommend Perform over SAP for
pushover analysis.  (I like Performs "hinge" elements much better than
those in SAP.)  I would be careful using SAP to model a steel frame,
especially if you are doing a nonlinear time history.  If you are
sharpening your pencil that much, you have to be certain that you include
all of the misc. stuff (such as panel zone stiffness and strength).

Hope this helps.

Mark J. Redlinger
Degenkolb Engineers
620 SW 5th Avenue, Suite 1100
Portland, Oregon  97204-1425

I could really use your help on a matter conserning SAP2000.What i'm trying
to do is study a steel frame and its plastic mechanism.I'm really having
problems with the nonlinear dynamic analysis.How can we assign the plastic1
element in SAP2000?Should we add joints close to the given ones and draw it
there?Also at which direction shall we apply the nonlinear
behaviour?Working with SAP2000 is easy to apply a pushover analysis with
plastic hinges but how about the nonlinear dynamic analysis? I would be
grateful if anyone could point me how we can draw these Nllink elements.
I would be really glad if you could reply to my question since i can't find
any help at all about this matter(plastic analysis with SAP200nl) or give
me some advise where i can find something useful on the Internet.

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