Static loads more than frequency response

[MACH.No]

Hi All,

i m trying to do a vibrational analyis on a structure which is excited by a vibrating force of 80KN at 50Hz. To check the stresses level and compare them with the related standard allowables and fatigue allowables I tried to get stress results out of frquency response. But when I compare the results with the static stresses itself ( having 80kn load in static enviroment) the values in static condition is higher. What can be the reasons?

thanks

[John_Holtz · Accepted solution]

Hi @MACH.No 

It could be that your model has mass and inertia, and therefore the displacement (and stress) in a dynamic situation is smaller than in a static situation.

Here is a generic plot showing the transmissibility ratio for a frequency response analysis. When the forcing frequency is larger than the natural frequency, the displacements are smaller.