I am dealing with mat foundation resting on soil. I am supposed to assign subgrade modulus to the mat in YONLY direction. But, what would happen if i assigned Fixed But with FY as some stiffness. will it behave same or different.?
No, the results should be the same. The only difference is that in the Fixed But command you need to calculate this spring stiffness of the node manually, while in the Plate Mat option this is done automatically based on the subgrade modulus value which you enter.