Defining a Displacement Constraint

In CONSTRAINT_ITEM dialog, create a COMBINED_ITEM design response with VAR_OPER = SUB_ABS.

To create the individual design response for each of the two displacements, press "?" key in the VARIABLE_1 field.

Press New in the appeared dialog, then choose TOSCA_DRESP.

In the DRESP dialog, choose TARGET = NODE and TYPE = DISP_Z (in case of the displacement in z-direction).

Enter the node ID in the NID field and the load case(s) in the LC_SET field.

Double click on the name of the design response in TOSCA HELP window so that this design response is entered in VARIABLE_1 field of the COMBINED_ITEM design response.

Repeat the steps for the second displacement entered in VARIABLE_2 field.

Define a design response (DRESP) for the displacement of the first node.

For a list of existing types, see Overview of Displacement and Rotation.

Note: The total absolute value cannot be used as design response.

Define a design response for the displacement of the second node, similar to the first one.

To define a design response with the difference of the nodal displacement from the two nodes, choose Command > DRESP.

In the DRESP dialog, select DefType = Operator and Operator = SUB_ABS.

Define a second constraint for the relative material volume.

Only a few elements will be removed in the short arm in order to obtain equal displacements of the two arms. In most cases the intention is to have a structure with a given weight and the maximum stiffness.

Define the objective function as minimization of the compliance of the whole model. This is defined as the sum of the strain energy of all elements (ALL_ELEMENTS element group).