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RE: Resonance

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Namely, it depends on the mass participation factors of each of the related frequencies.
As you have stated, the machinery produces up and down forces. That means, you should consider the up and down frequencies of the structure with its mass participations in that direction. If the modes of the structure you have found belongs to the lateral sway mode (bending mode of the whole structure), comparing these modes with those obtained for the machinery has no physical meaning.
So, whether resonance will be important or not, firstly you should calculate the vertical vibration mode of supporting element only, rather than calculating it for the whole structure. If either mode coincides, you should consider resonance.
From my past experiences, the best way to solve such a problem is to carry out a time history analysis. In that case, you will be able to capture the vibration induced effects in the structural elements.

Best regards,

TEM Eng&Con.Ltd.Co.

Say I have a structure supporting a machinery. I did a modal analysis and
determine that the natural frequencies (in cps) of the structure are as
follows: mode 1 = 3, mode 2 = 5, mode 3 = 10. The rated frequency of the
machinery = 5. The machinery has up & down vibration which is more similar
with mode 1 than mode 2.
Should I expect resonance problem? I'll appreciate any input.
Thanks & regards!

Rainier Catubig
San Diego, California

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