Equivalent static vs. response spectrum: a comparison of two methods

Developments in computer hardware and software have made analysis techniques that were formerly too expensive within the reach of most project budgets. Foremost among these has been seismic response spectrum analysis. This method yields much more accurate results than the equivalent static approach. The problem with using response spectrum analysis exclusively in the design of deflection controlled structures, such as astronomical telescopes, is that the nature of the structure minimizes the benefits of the approach. A typical response spectrum from Eurocode 8 deals with a range of natural periods between 0.1 and 5 seconds. These correspond to a frequency range of 0.2 to 10 Hz. The typical telescope structure has a minimum frequency of around 10 Hz. or greater. The result is that the response spectrum analysis involves only a narrow band of frequencies and accelerations. This result could be reliably obtained using an equivalent static analysis approach.