Array, If you don't put in all the mass, the natural frequencies will be higher than the frequencies experimentally measured on the structure, so basically if I have some parts within my structure, like motors or transformers as you said, which won't carry any load since the load will be carried by the main structure (which is actually holding these motors or transformers like under high accelerations) but you said that still these masses must be modelled as point/distributed masses while conducting the modal analysis. But I am trying to find out the natural frequencies of my main load carrying structure; still is it necessary for me to input these masses in my model while conducting modal analysis?nIn the second paragraph of yours, Typically a range of frequencies are specified and the solution tells you how much displacement magnitude every point in the model has for each excitation frequency in the analysis., So basically the displacement of each and every point within my model is dependent on two parameters: i) the excitation frequency at which the structure is forced to vibrate at ii) The magnitude of the periodic load. Can I also see the stresses within my Harmonic analysis, to see if the structure is failing or not under the specified load and excitation frequency?nAnd, this is kind of like a general question, should I expect failure within my main load carrying structure to occur if the excitation freq is not the same or near the natrual freq of it, but the amplitude of the load applied is very high which may cause some significant deformations within the structure, eventually leading it to fail? And also vice versa, meaning that can it be possible for the structure to not fail if the excitation freq is the same or near to the natural freq, but the amplitude of the load applied is not big enough to cause any plastic failure or fracture?nWill the response to my applied periodic load differ if I change the location at which the load is applied on my structure?nI must also confess that I got a little bit confused because if you think of a bridge which has a specific natural frequency, then I can vary the excitation frequencies in a range. But if wind is causing the excitation, then how will I get the load that should be inputted into the Harmonic response?nAnd one more thing, can you also kindly tell me the use of 'participation factor', 'effective mass', and 'ratio of effective mass to total mass'?n