Hi,
I have read the issue in the technical reference manual. My problem was that I did not know what happens when I donīt indicate the displacements of each affected anchor to each spectrum. In manual says that in the default situation, the program entry the corresponding to the lowest frecuency. But, the lowest frecuency of each spectrum?, the lowest frecuency in each spectrum is zero, and the acceleration is not the higest, my system donīt enter in resonance with a so low frecuency and this is not the most unfavorable situation. I donīt know if I have understood it.

Thank you smile