To assign a mat foundation support to a surface, use the following procedure.

1. Select one or more surfaces that will be supported.
2. On the Surfaces ribbon tab, select the Mat Foundation tool in the Mat and Edge Supports group.
   
   The Assign Mat Foundation dialog opens.
3. Select the Direction in which the foundation reaction acts. Typically, this will be the Y direction, which will apply the spring in the global Y direction while fixing movement along the global X and Z directions as well as fixing rotation about the Y axis.
4. Type the Subgrade modulus value to use for the soil modeling. This is the stiffness parameter used to describe the soil supporting the footing.
5. Select the Axial Behavior:
   • Complete - the mat foundation is capable of resisting both positive and negative force along the selected Direction
   • Compression Only - the mat foundation is capable of only resisting compressive force (i.e., towards the joint) along the selected Direction (use this option for foundations which cannot resist uplift)
6. Click OK.