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Re: FEM and Cables-Reply

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Drinkwater wrote:
>Real cable is geometric nonlinear, and has a 6X6 stiffness matrix for 3D
>cables. The stiffness matrix also can be formulated into 6x7 matrix with
>a constraint for advanced applications. Standard input for elastic
>catenary cable includes the following:
>(1) coordinates of two joints
>(2) unit weight
>(3) unstrained length (it can be < joint distance.)
>(4) material constants (E and thermal expansion coefficients)

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.

>Standard procedure does not ask users to assume a pretension. A good
>cable program can analyze cable nets, cable-stayed roof and bridge,
>cable truss, or other type of cable-supported structures. Dynamic
>analysis will be more complex.

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)