Thanks for your reply Sir,

No it is not necessary to have first mode between the 20 and 2000 Hz. I was just concerned that if my modal frequencies are greater than the frequency range in Random vibration then how the MSUP will perform the calculation will it be accurate or not.

I have checked density, mass and Young's modulus all are correct.

Will you please tell me how can I improve my ratio of effective mass to total mass as increasing no of  modes will increase computational efforts

Thanks in advance.