Select the Define
Structural Interface 
option from the toolbar or
the Properties menu.
In the Define Structural Interface Properties dialog, select the Joint/Liner/Joint combination which makes up the Structural Interface.
Phase2 Model > Support > Piles and Geosynthetics
The Define Structural Interface option is used to select the joint/liner/joint combination which is associated with a Structural Interface boundary.
To define the properties of a Structural Interface:
First define the properties of the individual components of the Structural Interface.
Use the Define Liners option to define the properties of the support component.
Use the Define Joints option to define the properties of the joint components.
Select the Define
Structural Interface option from the toolbar or
the Properties menu.
In the Define Structural Interface Properties dialog, select the Joint/Liner/Joint combination which makes up the Structural Interface.
NOTE: for the purpose of assigning the Joint type, a Structural Interface has a positive and a negative side. This allows you to apply a different Joint type on either side of the Structural Interface, if desired.
When you are finished selecting the components of the Structural Interface, select OK.