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Re: FEM and Cables-Reply

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Yes. I think the confusion comes here from calling the same thing with two
different names. Robot 97 is applying true elastic catenary cable with
first-order displacement, du,  and small gradients, du/dx. Its cable element
is not a rough approximation like in some other popular programs.

Best regards,

Jack Kucharewicz

-----Original Message-----
From: Waterman Drinkwater <Drinkwater(--nospam--at)EQUATION.COM>
To: 'seaint(--nospam--at)seaint.org' <seaint(--nospam--at)seaint.org>
Date: Thursday, April 08, 1999 3:08 PM
Subject: RE: FEM and Cables-Reply


>Catenary cable is geometrical nonlinear. Nonlinear geometry is not
>identical to "large displacement". It would be better to verify if the
>cable member programmed in Robot 97 are real elastic catenary cable or
>some sort of approximation.
>
>Elastic cable uses "linear stress-strain relation" and the "first-order
>displacement". First-order displacement does NOT formulate "large
>displacements". Because of geometrical nonlinearity, the temperature
>change and thermal coefficient appear in the stiffness matrix. For more
>introduction of elastic cables, there is a book "cable structures" by
>Max Irvine.
>
>In fact, the nonlinearity in cable equation is not from "displacement".
>Many books in engineering mechanics introduce catenary cables. Those
>cables (assumed to be undeformable in fundamental engineering mechanics)
>are formulated without a consideration of "displacement", but the cable
>equation is always nonlinear. This is a simple illustration the
>nonlinearity in cable is not from "large displacement".
>
>
>
> ----------
> From:  jk [SMTP:jk(--nospam--at)issstanford.com]
> Sent:  Thursday, April 08, 1999 4:12 PM
> To:  seaint(--nospam--at)seaint.org
> Subject:  Re: FEM and Cables-Reply
>
> Robot 97, structural analysis and design software,  is
>specializing in cable
> elements. They very realistically implemented. They are treated
>as
> - non-linear elements with large displacements,
> - have coordinates of two joints
> - on which you can impose the nodal load
> - you can inlclude the self-weight of a cable,
> - you can include a temperature load
> - you can impose the initial shortening/elengation or prestress
>load,
> - you can load the deformed shape of the cable with concentrated
>or
> distributed load,
> - you can specify the E and thermal expansion.
>
> Robot 97 can  analyze all the structure types you mentioned. Our
>clients
> have used Robot successfully to model very complex structures
>like stadiums,
> bridges or nets. Also, given that Robot 97 has the best user
>interface and
> postprocessor among structural engineering software to model
>cable
> structures, I think you should take a look at this program.
>
> BTW, original message mentioned also tension-only and
>compression-only
> elements: Robot 97 allows for such application.
>
> Feel free to contact us. Best regards,
>
> Jack Kucharewicz
> ___________________________
> Integrated Structural Software
> 848 Stanford University Ave.
> Palo Alto, CA 94301, USA
> toll free: (888) ISS-8491
> phone:  (650) 853-8491
> fax:  (650) 853-8490
> e-mail: jk(--nospam--at)issstanford.com
> >
> >
> >
>
>
>
>
>
>