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Re: RISA3D vs ETABS

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I do not agree at all.

We use both, and we use ETABS extensively. The fact is they are very different programs, and ETABS requires a higher level of sophistication on the users part to ensure proper modeling and results. ETABS is much more powerful than RISA, but like any true FEA program requires cautious and judicious use with a clear understanding of the different elements and what they are doing in the model, and how the element stiffnesses affect the analysis run. RISA is more simple with "text book" analysis the way you learned classical analysis techniques. RISA has some very useful features, and for certain types of structures and analysis may be the program of choice; for other types there is no question ETABS is superior.

There have been bugs in the software, but screwed up mesh and node incompatibility is not a program bug, it is a user bug. I have always found tech support to be very helpful, you just have to be asking the right questions. Programs like ETABS take commitment on the part of the user and the company that implements it. I am sure any of the other advanced FEA programs require an equal commitment in time and understanding.


Paul Feather PE, SE
www.SE-Solutions.net
pfeather(--nospam--at)SE-Solutions.net
----- Original Message ----- From: "Joseph Harouni" <jharouni(--nospam--at)sbcglobal.net>
To: "Suresh Acharya" <SAcharya(--nospam--at)ci.alameda.ca.us>; <seaint(--nospam--at)seaint.org>
Sent: Wednesday, February 08, 2006 3:30 PM
Subject: Re: RISA3D vs ETABS


Wow, thank you for the info.
Joseph
On Feb 8, 2006, at 3:19 PM, Suresh Acharya wrote:

Hi Joseph,
I have used both RISA and ETABS until 2002.

RISA is good at what it promises, and is simple.  But ETABS promises
more than what it can do reliably.

ETABS is full of bugs, so much that they produces patches every often.
Sometime results are riddiculous. Once I found the seismic mass was
wrong, although it calculated gravity reactions correctly. When plate
elements are used to model concrete slabs, it can generates meshes
automatically - but there is no connection between individual  meshes and
the beams or girders - when you look at the mode shapes, you see they
are vibrating independently.

Modeling the main frames with ETABS is fine, as long as you verify
results manually. But I would not rely on ETABS' other builit-in
features which are meant to make you life easier, but in fact it may
make your life miserable.

When you call ETABS, you will be feeling that you are not talking to a
structural engineer, but rather more like a programner with some
engineering background. They are changing the user interface and
modeling concept (except, probably the core FEA engine which was  written
in FORTRAN at UC Berkeley) every often that everytime is loaded  with new
bugs. Besides, they are still using Visual Basic to write routines -
that is the reason why it is sluggish even in new computers.





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