I have the records of acceleration in some points of a foundation of a building. To design it I need to put a slab (with a rigid diaphragm) with area springs (for the soil-structure interaction). But, when I display the results I get a bigger acceleration in the points that I am applying my input. It looks like the springs are distorting the seismic ground motion, as if it was applied to the bottom of them. How should I apply my acceleration record directly to the slab but maintaining the springs?