The trucksim data is inadequate to generate a useful psd because the sampling frequency is much lower than required. Have you done a Modal analysis of your structure? What is the frequency of the first mode?
Instead of trucksim data, use a published psd table for truck transport on a rough road. I expect you could find that on the internet.
The easy way to convert an excel worksheet to an ascii file is to Save As a Comma Separated Values (.csv) file type.
You are navigating away from the AIS Discovery experience