What is the design response spectrum?

The response spectrum which is used for the seismic analysis of a new structure for an anticipated or upcoming earthquake. From the past seismological data of a particular location, a single response spectrum was drawn using a single earthquake signal alone cannot be used for analysing the behaviour of new structures for future earthquakes. Because Earthquake – A having the peak ground acceleration amplitude at a certain frequency is never Similar to Earthquake – B having the same peak ground acceleration value at a different frequency. Hence no two earthquakes are similar to each other. The stresses induced in a building structure having a natural frequency closer to that of earthquake – A is higher as compared to the stresses induced in the same building structure due to earthquake – B which has a significant frequency component far away from the natural frequency of the building. To overcome this, the past 25 numbers of earthquake signals of a particular location are considered and their individual response spectrum is plotted in the same Vs frequency plot. The envelope drawn over the Peaks of all 25 Response spectra is called the design response spectrum. The number of previous earthquakes considered for plotting the design response Spectrum may vary from standard to standard. The design response spectrum curve is smooth in contrast to the spiky response spectrum as shown in the figure below.

The design response spectrum can be plotted in vs frequency plot or vs Time period plot as shown in the figure below.