Dynamic analysis

I am performing dynamic analysis on PLAXIS 2D of model size 35x15 m. The model was excited through a sinusoidal load of frequency 31 Hz. However the Rayleigh wave velocity was found 93 Hz. This leads to Rayleigh wavelength of 3 m. According to Kramer, the element size should be less than (3/8= 0.375 m).  I am facing difficulty to discretize meshes of this dimension. When I provide a element dimension as 0.375 in mesh options., It automatically changes to some other value. How could I create meshes of such sizes. 

Thanks

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  • Dear Sir,

    Could you please help me to introduce the steps to calculate the first resonance frequency of the soil layer shown in above figures?

    The dynamic load of 31 Hz was applied at the axis of symmetry of surface.

    I have read the PLAXIS manual in which the formula was given but I am more interested to calculate it through PLAXIS.

    I have also gone through the tutorial 15 where free vibration and earthquake analysis of a building was performed but unable to make out of it.

    In a nutshell I have following issues.

    Do I need to create a structure to calculate the natural frequency of soil?

    Do I need to apply only horizontal static load to excite the system?

    Thank you.  

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