Multiframe allows you to rigidly link groups of joints together so that they move together in response to either static or dynamic loads.  This has a twofold benefit.  Firstly, it allows you to simulate rigid structural elements such as a floor slab, and secondly it significantly reduces the size of the stiffness matrix resulting in lower memory requirements and faster analysis times.

Joints can be linked together on a degree-of-freedom basis.  This means some degrees-of-freedom can be linked together and others left independent.  In the case of a rigid floor slab for example, all the joints on that level could have their x, z and Øy deflections linked together to simulate the rigid translation and rotation of the slab while still allowing bending of the floor. When linking a rotational degree of freedom, Multiframe automatically selects the corresponding displacement degrees of freedom that must also be imposed to enforce rigid body motion in the plane of the rotation.

To rigidly link a group of joints

§    Select the joints to be linked in the Frame window

§    Choose Joints Linking from the Frame menu

§    Select a master joint.

In most cases the default master joint selected by Multiframe will be adequate. It is only when linked group intersect that the Master Joint would have to be changed to a joint contained in both linked groups of joints.

§    Type in a name for the group and select the degrees of freedom to be linked

The linked group of joints is displayed as a shaded area in the Frame window. The Master Joint in each group of linked joints is also highlighted using circle of darker shading.

The properties of a linked group of joints can be edited by double clicking on the linked region displayed in the Frame window.

The linked joints are also displayed in tabular form in the Data window.  Choose Linked Joints from the Data sub-menu to display this table or click on the Linked Joints tab at the bottom of the Data Window. The rows of this table corresponding to the Master Joints are shown in bold.

The linking is defined for the global XYZ directions.  If you link two or more joints together in the X direction then they will be locked together for any movement in the global X direction.

The following restrictions apply when linking joints and to the restraints, or supports, attached or applied to the linked joints.

·                      Joints may be common to several groups of linked joints provided that the master joint in all of the intersecting groups is the same joint.

·                      Prescribed displacements can only be applied to linked joints that are master joints.

·                      Restraints to linked degrees of freedom must be applied to the master joint

·                      The reactions in the direction of the linked degrees of freedom for a group of linked joint are computed at the master joint.

The compliance of the frame to these rules is tested when the user analyses the frame.

The joints linked together in a linked group may be selected using the Linked Joints command in the Select menu.  From version 8.6 of Multiframe the elements selected when the joints are linked are also stored with the linked group.  These will also be selected when the Select Linked Joints command is executed.