Cross-link - Defining a new connection of intersecting entities

Any two intersecting entities may be connected in a point called cross-link. The cross-link ensures that the two entities remain undivided but act together and allow for transfer of internal forces from one entity to the other one.

Cross-links are also used in models of scaffolding where they represent couplers. For this also a library of couplers can be used.

Parameters of cross-link

Name

Defines the name of the cross-link.

Type

There are three types available:

- fixed - transfers all internal forces from one entity to another,

- hinged - does not transfer bending moments,

- coupler - allows for linear on non-linear connection of two entities.

The cross-link of type coupler is available for users having the function “beam local nonlinearity” enabled. Also functionality “scaffolding” must be enabled.

The coupler is available for projects of type: Frame xz,  Frame xyz,  General xyz.

Hinge type

The type can be either (i) standard or (ii) library.

- standard - all the parameters of the cross-link can be input directly in the cross-link parameters,

- library - a predefined type of a coupler is read from the library (database).

Hinge type library

This item selects the type of a cross-link (coupler) from the library (database) of couplers.

u member 1

Displacement for the first connected member (its name can be seen at the bottom of the property dialogue) .

fi member 1

Rotation for the first connected member. This can be free / rigid / flexible / nonlinear.

Stiff - fi member 1

Torsional stiffness around the 1st member.

Fun - fi member 1

Specifies the non-linear function (fi versus moment) for member 1.

u member 2

Displacement for the second connected member (its name can be seen at the bottom of the property dialogue) .

fi member 2

Rotation for the second connected member. This can be free / rigid / flexible / nonlinear.

Stiff - fi member 2

Torsional stiffness around the 2nd member.

Fun - fi member 2

Specifies the non-linear function (fi versus moment) for member 2.

u cross-link

Displacement for the cross-link.

fi - cross-link

Rotation for the cross-link.

Stiff - fi cross-link

Torsional stiffness of the cross link (perpendicular to the plane defined by member1 and member 2).

Fun - fi cross-link

Specifies the non-linear function (fi versus moment) for the cross-link.

Connection > 1st member

Displays the first connected member.

Connection > 2nd member

Displays the first connected member.

Notes:

The axis of the connection is defined by the members of the cross-link:

- The first axis is assigned to the first member (i.e. the first member selected by the user during the definition of a new cross-link).

- The second axis is assigned to the second member (i.e. the second member selected by the user during the definition of a new cross-link).

- The third axis is perpendicular at the plane defined by member 1 and member 2.

In case the link definition is set on library, then all properties of the selected hinge type are read-only (they can be modified in the Hinge-type database (Coupler library).

If the structure type is “frame xz”, then the properties of “fi cross-link” are not displayed.

In case the functionality “local beam nonlinearity” is not selected, then type of fi cannot be “nonlinear”.

If the property “fi” is set to “free” or “rigid” then properties “stiff” and “fun” are not displayed.

If property “fi” is set to “flexible”, then property “fun” is not displayed.

If the members 1 and 2  are not perpendicular the “type of fi” in “fi member 1” and “fi member 2” cannot be set to nonlinear.  Only “fi cross-link” can be set to nonlinear.

If the user modifies the model and some cross-links between members that were perpendicular before the modification but became non-perpendicular after it) have nonlinear settings, then these couplers are removed by the program with the message: Couplers at cross-links are deleted because type became not-orthogonal”.

The procedure for the definition of a new cross-link

  1. Open function Cross-link

    1. either from menu Tree > Structure,

    2. or from tree menu service Structure.

  2. In the Property window specify the parameters of the cross-link.

  3. Select the 1D members that should be connected.

  4. Close the function.

  5. The cross-link is generated and displayed in the form of a thick dot with thin short lines along the connected 1D members.

It is possible to use an alternative procedure, which means that first, the selection of 1D members is made and only then the function is called. If applied, this procedure does not require the user to close the function but does not allow for the modification of cross-link parameters. They would have to be edited afterwards.