I am reading a textbook on fundamentals of vibrations and it has a very brief introduction to shock spectra. It mentions that
For comparison purposes, it is customary to use the response of an undamped single degree of freedom system to obtain the shock spectrum.
So is it that we always find the maximum response of an undamped single DOF system to get the shock spectrum? If yes, then how does it help us, because can't the response of the structure which I am analysing (say a building) be widly different from that of a single DOF system? For example, consider two shocks. The shock which seems "stronger" (higher maximum response in general) when using a single DOF system may actually be weaker when using my structure.
Also, just saying an undamped single DOF system seems vague because response to the same shock may differ for different single DOF systems. Is there a specific single DOF system that is used here (like the mass-spring system)?