I successfully ran a modal vibration analysis with the minimum and maximum footstep frequency values set to 1.5 Hz and 2.5 Hz, respectively. I tried re-running the modal analysis with the minimum and maximum footstep frequency values changed to 0.83 Hz (50 steps) and 1.67 Hz (100 steps), respectively. I received the following error: An error has occurred. 0.83 is not a valid value for Minimum Footstep Frequency. I modified my footstep frequency values and changed the minimum and maximum footstep frequency values to 1.0 Hz and 1.7 Hz, respectively. However, RAM Concept will not perform the modal analysis. The modal analysis ends very quickly, and the Max Response Factor Plan, Max RMS Acceleration Plan, and Max RMS Velocity Plan all appear as the image shown below.
Why am I unable to set a Minimum Footstep Frequency below 1.0 Hz? Why will RAM Concept not perform a modal analysis with the new footstep frequencies?
Regarding the use of 0.83 Hz for the minimum footstep frequency:
A walking rate of 50 steps per second seems extremely slow and does not seem likely to induce a resonant response. It would also tend to excite a floor with very low fundamental natural frequency (< 4 Hz), which are seemingly rare in concrete floors. I do not think the critical response will typically be lost by using a minimum walking frequency of 1 Hz instead of 0.83 Hz. Increasing the minimum footfall frequency as you noted is what we would recommend to eliminate the first error that you noted.
Regarding the problems with using 1 Hz for the minimum footfall frequency:
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Thanks for the advice. I was just looking for information about it. You have described the solution of the problem very simply and easily.