I have been focusing only on the first (lowest) frequency and calculate stress and deflection results based on that value as Steinberg indicates that this is where the highest deflection takes place. Why is this the case? If I wanted to calculate the results for higher modes, how would I take the higher frequency value into account? Is the energy dissipated (into heat?) as the frequency is increased? I have not found anything in his book (or others) that addresses this aspect.