What is floor response spectrum?

The design response spectrum helps in analysing the seismic behaviour of the primary structure. However, it cannot be used for analysing the behaviour of the secondary structure or a component mounted in the primary structure. Because the base acceleration seen by a tank mounted on the second floor of the primary structure is not the same as the original ground acceleration of a primary structure. The primary structure acts as a band pass filter because the primary structure will not excite to very low frequencies or very high frequencies as compared to its natural frequency. Hence the primary structure will allow the earthquake signals having a frequency content close to its natural frequency. The peak responses of a particular floor at a given elevation are related to the natural frequency of the primary structure. The response of the tank on floor-1 is not similar to that of the same tank on floor-2 of the same primary building. Hence the floor response spectra are developed for different floors of the primary structure. The floor response spectra are drawn in a similar manner as that of the design response spectrum by drawing the envelope over the peaks of past response spectra.