Winkler foundatios is a sort of beam with springs (an example in the image below). For this reason I thought to use BEAM188 to represent che skin (thikness of the skin 3 mm orthotropic material) and COMBIN14 to represent the springs (which represents the core of the sandwich made with isotropic material). I wanted to perform 2D analysis. The spring costant is equal to 2*Ec/tc where the Ec is the elastic moduli of the core (100MPa) and tc its thickness (24mm). In my case the spring constant is equal to 8.33. So I set the real constant for the COMBIN14. On the other hand, I choose BEAM188 with square section (3x3 mm^2) with cubic shape function. I imput the skin orthotropic material in Ansys. Then I create a line and meshed it with BEAM188 element. After that i put COMBIN14 elements in the same way that the image below show. Then I impose symmetry BC's on Z axis, block all DOF on one side of the beam except Zrotations, and the same on the other side of the beam where I left free Z rotations and ux displacement. I also blocked all DOF at the base of the springs. Then I impose a compressive force on one hand of the beam, and do the buckling analysis. What am I doing wrong?