Answer:
In the example, I have created a model with a 0.5 m wide member.
Assuming a foundation of 200 kN/m³, the translational spring constant corresponds to 200 kN/m³ = 100 kN/m² * 1 / 0.5 m.
If you want to support the member with springs, multiply the foundation by the member width (100 kN/m³).
If you now want to additionally consider the surface friction, you have to include the perimeter in the calculation (see the solid example).
